TypeScript/src/services/findAllReferences.ts

/* @internal */
namespace ts.FindAllReferences {
    export interface SymbolAndEntries {
        readonly definition: Definition | undefined;
        readonly references: ReadonlyArray<Entry>;
    }

    export const enum DefinitionKind { Symbol, Label, Keyword, This, String }
    export type Definition =
        | { readonly type: DefinitionKind.Symbol; readonly symbol: Symbol }
        | { readonly type: DefinitionKind.Label; readonly node: Identifier }
        | { readonly type: DefinitionKind.Keyword; readonly node: Node }
        | { readonly type: DefinitionKind.This; readonly node: Node }
        | { readonly type: DefinitionKind.String; readonly node: StringLiteral };

    export const enum EntryKind { Span, Node, StringLiteral, SearchedLocalFoundProperty, SearchedPropertyFoundLocal }
    export type NodeEntryKind = EntryKind.Node | EntryKind.StringLiteral | EntryKind.SearchedLocalFoundProperty | EntryKind.SearchedPropertyFoundLocal;
    export type Entry = NodeEntry | SpanEntry;
    export interface DeclarationNodeWithStartAndEnd {
        start: Node;
        end: Node;
    }
    export type DeclarationNode = Node | DeclarationNodeWithStartAndEnd;
    export interface NodeEntry {
        readonly kind: NodeEntryKind;
        readonly node: Node;
        readonly declaration?: DeclarationNode;
    }
    export interface SpanEntry {
        readonly kind: EntryKind.Span;
        readonly fileName: string;
        readonly textSpan: TextSpan;
    }
    export function nodeEntry(node: Node, kind: NodeEntryKind = EntryKind.Node): NodeEntry {
        return {
            kind,
            node: (node as NamedDeclaration).name || node,
            declaration: getDeclarationForDeclarationSpanForNode(node)
        };
    }

    export function isDeclarationNodeWithStartAndEnd(node: DeclarationNode): node is DeclarationNodeWithStartAndEnd {
        return node && (node as Node).kind === undefined;
    }

    function getDeclarationForDeclarationSpanForNode(node: Node): DeclarationNode | undefined {
        if (isDeclaration(node)) {
            return getDeclarationForDeclarationSpan(node);
        }

        // TODO(shkamat)::
        // JSXOpeningElement or JSXElement for tagName ?
        if (!node.parent) return undefined;

        if (!isDeclaration(node.parent) && !isExportAssignment(node.parent)) {
            // Special property assignment in javascript
            if (isInJSFile(node)) {
                const binaryExpression = isBinaryExpression(node.parent) ?
                    node.parent :
                    isPropertyAccessExpression(node.parent) &&
                        isBinaryExpression(node.parent.parent) &&
                        node.parent.parent.left === node.parent ?
                        node.parent.parent :
                        undefined;
                if (binaryExpression && getAssignmentDeclarationKind(binaryExpression) !== AssignmentDeclarationKind.None) {
                    return getDeclarationForDeclarationSpan(binaryExpression);
                }
            }

            // Handle computed property name
            const propertyName = findAncestor(node, isComputedPropertyName);
            return propertyName ?
                getDeclarationForDeclarationSpan(propertyName.parent) :
                undefined;
        }

        if (isConstructorDeclaration(node.parent) ||
            node.parent.name === node || // node is name of declaration, use parent
            // Property name of the import export specifier or binding pattern, use parent
            ((isImportOrExportSpecifier(node.parent) || isBindingElement(node.parent))
                && node.parent.propertyName === node) ||
            isExportAssignment(node.parent) && node.parent.expression === node) {
            return getDeclarationForDeclarationSpan(node.parent);
        }

        return undefined;
    }

    export function getDeclarationForDeclarationSpan(node: NamedDeclaration | BinaryExpression | ForInOrOfStatement | undefined): DeclarationNode | undefined {
        if (!node) return undefined;
        switch (node.kind) {
            case SyntaxKind.VariableDeclaration:
                return !isVariableDeclarationList(node.parent) || node.parent.declarations.length !== 1 ?
                    node :
                    isVariableStatement(node.parent.parent) ?
                        node.parent.parent :
                        isForInOrOfStatement(node.parent.parent) ?
                            getDeclarationForDeclarationSpan(node.parent.parent) :
                            node.parent;

            case SyntaxKind.BindingElement:
                return getDeclarationForDeclarationSpan(node.parent.parent as NamedDeclaration);

            case SyntaxKind.ImportSpecifier:
                return node.parent.parent.parent;

            case SyntaxKind.ExportSpecifier:
            case SyntaxKind.NamespaceImport:
                return node.parent.parent;

            case SyntaxKind.ImportClause:
                return node.parent;

            case SyntaxKind.JsxAttribute:
                return (node as JsxAttribute).initializer === undefined ?
                    undefined :
                    node;

            case SyntaxKind.BinaryExpression:
                return isExpressionStatement(node.parent) ?
                    node.parent :
                    node;

            case SyntaxKind.ForOfStatement:
            case SyntaxKind.ForInStatement:
                return {
                    start: (node as ForInOrOfStatement).initializer,
                    end: (node as ForInOrOfStatement).expression
                };

            case SyntaxKind.PropertyAssignment:
            // TODO(shkamat):: Should we show whole object literal instead?
            case SyntaxKind.ShorthandPropertyAssignment:
                return isArrayLiteralOrObjectLiteralDestructuringPattern(node.parent) ?
                    getDeclarationForDeclarationSpan(
                        findAncestor(node.parent, node =>
                            isBinaryExpression(node) || isForInOrOfStatement(node)
                        ) as BinaryExpression | ForInOrOfStatement
                    ) :
                    node.kind === SyntaxKind.PropertyAssignment ?
                        node :
                        undefined;

            default:
                return node;
        }
    }

    export interface Options {
        readonly findInStrings?: boolean;
        readonly findInComments?: boolean;
        /**
         * True if we are renaming the symbol.
         * If so, we will find fewer references -- if it is referenced by several different names, we still only find references for the original name.
         */
        readonly isForRename?: boolean;
        /** True if we are searching for implementations. We will have a different method of adding references if so. */
        readonly implementations?: boolean;
        /**
         * True to opt in for enhanced renaming of shorthand properties and import/export specifiers.
         * The options controls the behavior for the whole rename operation; it cannot be changed on a per-file basis.
         * Default is false for backwards compatibility.
         */
        readonly providePrefixAndSuffixTextForRename?: boolean;
    }

    export function findReferencedSymbols(program: Program, cancellationToken: CancellationToken, sourceFiles: ReadonlyArray<SourceFile>, sourceFile: SourceFile, position: number): ReferencedSymbol[] | undefined {
        const node = getTouchingPropertyName(sourceFile, position);
        const referencedSymbols = Core.getReferencedSymbolsForNode(position, node, program, sourceFiles, cancellationToken);
        const checker = program.getTypeChecker();
        return !referencedSymbols || !referencedSymbols.length ? undefined : mapDefined<SymbolAndEntries, ReferencedSymbol>(referencedSymbols, ({ definition, references }) =>
            // Only include referenced symbols that have a valid definition.
            definition && {
                definition: checker.runWithCancellationToken(cancellationToken, checker => definitionToReferencedSymbolDefinitionInfo(definition, checker, node)),
                references: references.map(toReferenceEntry)
            });
    }

    export function getImplementationsAtPosition(program: Program, cancellationToken: CancellationToken, sourceFiles: ReadonlyArray<SourceFile>, sourceFile: SourceFile, position: number): ImplementationLocation[] | undefined {
        const node = getTouchingPropertyName(sourceFile, position);
        const referenceEntries = getImplementationReferenceEntries(program, cancellationToken, sourceFiles, node, position);
        const checker = program.getTypeChecker();
        return map(referenceEntries, entry => toImplementationLocation(entry, checker));
    }

    function getImplementationReferenceEntries(program: Program, cancellationToken: CancellationToken, sourceFiles: ReadonlyArray<SourceFile>, node: Node, position: number): ReadonlyArray<Entry> | undefined {
        if (node.kind === SyntaxKind.SourceFile) {
            return undefined;
        }

        const checker = program.getTypeChecker();
        // If invoked directly on a shorthand property assignment, then return
        // the declaration of the symbol being assigned (not the symbol being assigned to).
        if (node.parent.kind === SyntaxKind.ShorthandPropertyAssignment) {
            const result: NodeEntry[] = [];
            Core.getReferenceEntriesForShorthandPropertyAssignment(node, checker, node => result.push(nodeEntry(node)));
            return result;
        }
        else if (node.kind === SyntaxKind.SuperKeyword || isSuperProperty(node.parent)) {
            // References to and accesses on the super keyword only have one possible implementation, so no
            // need to "Find all References"
            const symbol = checker.getSymbolAtLocation(node)!;
            return symbol.valueDeclaration && [nodeEntry(symbol.valueDeclaration)];
        }
        else {
            // Perform "Find all References" and retrieve only those that are implementations
            return getReferenceEntriesForNode(position, node, program, sourceFiles, cancellationToken, { implementations: true });
        }
    }

    export function findReferenceOrRenameEntries<T>(
        program: Program, cancellationToken: CancellationToken, sourceFiles: ReadonlyArray<SourceFile>, node: Node, position: number, options: Options | undefined,
        convertEntry: ToReferenceOrRenameEntry<T>,
    ): T[] | undefined {
        return map(flattenEntries(Core.getReferencedSymbolsForNode(position, node, program, sourceFiles, cancellationToken, options)), entry => convertEntry(entry, node, program.getTypeChecker()));
    }

    export type ToReferenceOrRenameEntry<T> = (entry: Entry, originalNode: Node, checker: TypeChecker) => T;

    export function getReferenceEntriesForNode(
        position: number,
        node: Node,
        program: Program,
        sourceFiles: ReadonlyArray<SourceFile>,
        cancellationToken: CancellationToken,
        options: Options = {},
        sourceFilesSet: ReadonlyMap<true> = arrayToSet(sourceFiles, f => f.fileName),
    ): ReadonlyArray<Entry> | undefined {
        return flattenEntries(Core.getReferencedSymbolsForNode(position, node, program, sourceFiles, cancellationToken, options, sourceFilesSet));
    }

    function flattenEntries(referenceSymbols: ReadonlyArray<SymbolAndEntries> | undefined): ReadonlyArray<Entry> | undefined {
        return referenceSymbols && flatMap(referenceSymbols, r => r.references);
    }

    function definitionToReferencedSymbolDefinitionInfo(def: Definition, checker: TypeChecker, originalNode: Node): ReferencedSymbolDefinitionInfo {
        const info = (() => {
            switch (def.type) {
                case DefinitionKind.Symbol: {
                    const { symbol } = def;
                    const { displayParts, kind } = getDefinitionKindAndDisplayParts(symbol, checker, originalNode);
                    const name = displayParts.map(p => p.text).join("");
                    const declaration = symbol.declarations ? first(symbol.declarations) : undefined;
                    return {
                        node: declaration ?
                            getNameOfDeclaration(declaration) || declaration :
                            originalNode,
                        name,
                        kind,
                        displayParts,
                        declaration: getDeclarationForDeclarationSpan(declaration)
                    };
                }
                case DefinitionKind.Label: {
                    const { node } = def;
                    return { node, name: node.text, kind: ScriptElementKind.label, displayParts: [displayPart(node.text, SymbolDisplayPartKind.text)] };
                }
                case DefinitionKind.Keyword: {
                    const { node } = def;
                    const name = tokenToString(node.kind)!;
                    return { node, name, kind: ScriptElementKind.keyword, displayParts: [{ text: name, kind: ScriptElementKind.keyword }] };
                }
                case DefinitionKind.This: {
                    const { node } = def;
                    const symbol = checker.getSymbolAtLocation(node);
                    const displayParts = symbol && SymbolDisplay.getSymbolDisplayPartsDocumentationAndSymbolKind(
                        checker, symbol, node.getSourceFile(), getContainerNode(node), node).displayParts || [textPart("this")];
                    return { node, name: "this", kind: ScriptElementKind.variableElement, displayParts };
                }
                case DefinitionKind.String: {
                    const { node } = def;
                    return { node, name: node.text, kind: ScriptElementKind.variableElement, displayParts: [displayPart(getTextOfNode(node), SymbolDisplayPartKind.stringLiteral)] };
                }
                default:
                    return Debug.assertNever(def);
            }
        })();

        const { node, name, kind, displayParts, declaration } = info;
        const sourceFile = node.getSourceFile();
        const result: ReferencedSymbolDefinitionInfo = {
            containerKind: ScriptElementKind.unknown,
            containerName: "",
            fileName: sourceFile.fileName,
            kind,
            name,
            textSpan: getTextSpan(isComputedPropertyName(node) ? node.expression : node, sourceFile),
            displayParts
        };
        if (declaration) {
            result.declarationSpan = isDeclarationNodeWithStartAndEnd(declaration) ?
                getTextSpan(declaration.start, sourceFile, declaration.end) :
                getTextSpan(declaration, sourceFile);
        }
        return result;
    }

    function getDefinitionKindAndDisplayParts(symbol: Symbol, checker: TypeChecker, node: Node): { displayParts: SymbolDisplayPart[], kind: ScriptElementKind } {
        const meaning = Core.getIntersectingMeaningFromDeclarations(node, symbol);
        const enclosingDeclaration = symbol.declarations && firstOrUndefined(symbol.declarations) || node;
        const { displayParts, symbolKind } =
            SymbolDisplay.getSymbolDisplayPartsDocumentationAndSymbolKind(checker, symbol, enclosingDeclaration.getSourceFile(), enclosingDeclaration, enclosingDeclaration, meaning);
        return { displayParts, kind: symbolKind };
    }

    export function toRenameLocation(entry: Entry, originalNode: Node, checker: TypeChecker, providePrefixAndSuffixText: boolean): RenameLocation {
        return { ...entryToDocumentSpan(entry), ...(providePrefixAndSuffixText && getPrefixAndSuffixText(entry, originalNode, checker)) };
    }

    export function toReferenceEntry(entry: Entry): ReferenceEntry {
        const documentSpan = entryToDocumentSpan(entry);
        if (entry.kind === EntryKind.Span) {
            return { ...documentSpan, isWriteAccess: false, isDefinition: false };
        }
        const { kind, node } = entry;
        return {
            ...documentSpan,
            isWriteAccess: isWriteAccessForReference(node),
            isDefinition: node.kind === SyntaxKind.DefaultKeyword
                || !!getDeclarationFromName(node)
                || isLiteralComputedPropertyDeclarationName(node),
            isInString: kind === EntryKind.StringLiteral ? true : undefined,
        };
    }

    function entryToDocumentSpan(entry: Entry): DocumentSpan {
        if (entry.kind === EntryKind.Span) {
            return { textSpan: entry.textSpan, fileName: entry.fileName };
        }
        else {
            const sourceFile = entry.node.getSourceFile();
            const result: DocumentSpan = { textSpan: getTextSpan(entry.node, sourceFile), fileName: sourceFile.fileName };
            if (entry.declaration) {
                result.declarationSpan = isDeclarationNodeWithStartAndEnd(entry.declaration) ?
                    getTextSpan(entry.declaration.start, sourceFile, entry.declaration.end) :
                    getTextSpan(entry.declaration, sourceFile);
            }
            return result;
        }
    }

    interface PrefixAndSuffix { readonly prefixText?: string; readonly suffixText?: string; }
    function getPrefixAndSuffixText(entry: Entry, originalNode: Node, checker: TypeChecker): PrefixAndSuffix {
        if (entry.kind !== EntryKind.Span && isIdentifier(originalNode)) {
            const { node, kind } = entry;
            const name = originalNode.text;
            const isShorthandAssignment = isShorthandPropertyAssignment(node.parent);
            if (isShorthandAssignment || isObjectBindingElementWithoutPropertyName(node.parent)) {
                const prefixColon: PrefixAndSuffix = { prefixText: name + ": " };
                const suffixColon: PrefixAndSuffix = { suffixText: ": " + name };
                return kind === EntryKind.SearchedLocalFoundProperty ? prefixColon
                    : kind === EntryKind.SearchedPropertyFoundLocal ? suffixColon
                    // In `const o = { x }; o.x`, symbolAtLocation at `x` in `{ x }` is the property symbol.
                    // For a binding element `const { x } = o;`, symbolAtLocation at `x` is the property symbol.
                    : isShorthandAssignment ? suffixColon : prefixColon;
            }
            else if (isImportSpecifier(entry.node.parent) && !entry.node.parent.propertyName) {
                // If the original symbol was using this alias, just rename the alias.
                const originalSymbol = isExportSpecifier(originalNode.parent) ? checker.getExportSpecifierLocalTargetSymbol(originalNode.parent) : checker.getSymbolAtLocation(originalNode);
                return contains(originalSymbol!.declarations, entry.node.parent) ? { prefixText: name + " as " } : emptyOptions;
            }
            else if (isExportSpecifier(entry.node.parent) && !entry.node.parent.propertyName) {
                return originalNode === entry.node ? { prefixText: name + " as " } : { suffixText: " as " + name };
            }
        }

        return emptyOptions;
    }

    function toImplementationLocation(entry: Entry, checker: TypeChecker): ImplementationLocation {
        const documentSpan = entryToDocumentSpan(entry);
        if (entry.kind !== EntryKind.Span) {
            const { node } = entry;
            return {
                ...documentSpan,
                ...implementationKindDisplayParts(node, checker)
            };
        }
        else {
            return { ...documentSpan, kind: ScriptElementKind.unknown, displayParts: [] };
        }
    }

    function implementationKindDisplayParts(node: Node, checker: TypeChecker): { kind: ScriptElementKind, displayParts: SymbolDisplayPart[] } {
        const symbol = checker.getSymbolAtLocation(isDeclaration(node) && node.name ? node.name : node);
        if (symbol) {
            return getDefinitionKindAndDisplayParts(symbol, checker, node);
        }
        else if (node.kind === SyntaxKind.ObjectLiteralExpression) {
            return {
                kind: ScriptElementKind.interfaceElement,
                displayParts: [punctuationPart(SyntaxKind.OpenParenToken), textPart("object literal"), punctuationPart(SyntaxKind.CloseParenToken)]
            };
        }
        else if (node.kind === SyntaxKind.ClassExpression) {
            return {
                kind: ScriptElementKind.localClassElement,
                displayParts: [punctuationPart(SyntaxKind.OpenParenToken), textPart("anonymous local class"), punctuationPart(SyntaxKind.CloseParenToken)]
            };
        }
        else {
            return { kind: getNodeKind(node), displayParts: [] };
        }
    }

    export function toHighlightSpan(entry: Entry): { fileName: string, span: HighlightSpan } {
        const documentSpan = entryToDocumentSpan(entry);
        if (entry.kind === EntryKind.Span) {
            return {
                fileName: documentSpan.fileName,
                span: {
                    textSpan: documentSpan.textSpan,
                    kind: HighlightSpanKind.reference
                }
            };
        }

        const writeAccess = isWriteAccessForReference(entry.node);
        const span: HighlightSpan = {
            textSpan: documentSpan.textSpan,
            kind: writeAccess ? HighlightSpanKind.writtenReference : HighlightSpanKind.reference,
            isInString: entry.kind === EntryKind.StringLiteral ? true : undefined,
        };
        if (documentSpan.declarationSpan) {
            span.declarationSpan = documentSpan.declarationSpan;
        }
        return { fileName: documentSpan.fileName, span };
    }

    function getTextSpan(node: Node, sourceFile: SourceFile, endNode?: Node): TextSpan {
        let start = node.getStart(sourceFile);
        let end = (endNode || node).getEnd();
        if (node.kind === SyntaxKind.StringLiteral) {
            Debug.assert(endNode === undefined);
            start += 1;
            end -= 1;
        }
        return createTextSpanFromBounds(start, end);
    }

    export function getTextSpanOfEntry(entry: Entry) {
        return entry.kind === EntryKind.Span ? entry.textSpan :
            getTextSpan(entry.node, entry.node.getSourceFile());
    }

    /** A node is considered a writeAccess iff it is a name of a declaration or a target of an assignment */
    function isWriteAccessForReference(node: Node): boolean {
        const decl = getDeclarationFromName(node);
        return !!decl && declarationIsWriteAccess(decl) || node.kind === SyntaxKind.DefaultKeyword || isWriteAccess(node);
    }

    /**
     * True if 'decl' provides a value, as in `function f() {}`;
     * false if 'decl' is just a location for a future write, as in 'let x;'
     */
    function declarationIsWriteAccess(decl: Declaration): boolean {
        // Consider anything in an ambient declaration to be a write access since it may be coming from JS.
        if (!!(decl.flags & NodeFlags.Ambient)) return true;

        switch (decl.kind) {
            case SyntaxKind.BinaryExpression:
            case SyntaxKind.BindingElement:
            case SyntaxKind.ClassDeclaration:
            case SyntaxKind.ClassExpression:
            case SyntaxKind.DefaultKeyword:
            case SyntaxKind.EnumDeclaration:
            case SyntaxKind.EnumMember:
            case SyntaxKind.ExportSpecifier:
            case SyntaxKind.ImportClause: // default import
            case SyntaxKind.ImportEqualsDeclaration:
            case SyntaxKind.ImportSpecifier:
            case SyntaxKind.InterfaceDeclaration:
            case SyntaxKind.JSDocCallbackTag:
            case SyntaxKind.JSDocTypedefTag:
            case SyntaxKind.JsxAttribute:
            case SyntaxKind.ModuleDeclaration:
            case SyntaxKind.NamespaceExportDeclaration:
            case SyntaxKind.NamespaceImport:
            case SyntaxKind.Parameter:
            case SyntaxKind.ShorthandPropertyAssignment:
            case SyntaxKind.TypeAliasDeclaration:
            case SyntaxKind.TypeParameter:
                return true;

            case SyntaxKind.PropertyAssignment:
                // In `({ x: y } = 0);`, `x` is not a write access. (Won't call this function for `y`.)
                return !isArrayLiteralOrObjectLiteralDestructuringPattern((decl as PropertyAssignment).parent);

            case SyntaxKind.FunctionDeclaration:
            case SyntaxKind.FunctionExpression:
            case SyntaxKind.Constructor:
            case SyntaxKind.MethodDeclaration:
            case SyntaxKind.GetAccessor:
            case SyntaxKind.SetAccessor:
                return !!(decl as FunctionDeclaration | FunctionExpression | ConstructorDeclaration | MethodDeclaration | GetAccessorDeclaration | SetAccessorDeclaration).body;

            case SyntaxKind.VariableDeclaration:
            case SyntaxKind.PropertyDeclaration:
                return !!(decl as VariableDeclaration | PropertyDeclaration).initializer || isCatchClause(decl.parent);

            case SyntaxKind.MethodSignature:
            case SyntaxKind.PropertySignature:
            case SyntaxKind.JSDocPropertyTag:
            case SyntaxKind.JSDocParameterTag:
                return false;

            default:
                return Debug.failBadSyntaxKind(decl);
        }
    }
}

/** Encapsulates the core find-all-references algorithm. */
/* @internal */
namespace ts.FindAllReferences.Core {
    /** Core find-all-references algorithm. Handles special cases before delegating to `getReferencedSymbolsForSymbol`. */
    export function getReferencedSymbolsForNode(position: number, node: Node, program: Program, sourceFiles: ReadonlyArray<SourceFile>, cancellationToken: CancellationToken, options: Options = {}, sourceFilesSet: ReadonlyMap<true> = arrayToSet(sourceFiles, f => f.fileName)): ReadonlyArray<SymbolAndEntries> | undefined {
        if (isSourceFile(node)) {
            const reference = GoToDefinition.getReferenceAtPosition(node, position, program);
            const moduleSymbol = reference && program.getTypeChecker().getMergedSymbol(reference.file.symbol);
            return moduleSymbol && getReferencedSymbolsForModule(program, moduleSymbol, /*excludeImportTypeOfExportEquals*/ false, sourceFiles, sourceFilesSet);
        }

        if (!options.implementations) {
            const special = getReferencedSymbolsSpecial(node, sourceFiles, cancellationToken);
            if (special) {
                return special;
            }
        }

        const checker = program.getTypeChecker();
        const symbol = checker.getSymbolAtLocation(node);

        // Could not find a symbol e.g. unknown identifier
        if (!symbol) {
            // String literal might be a property (and thus have a symbol), so do this here rather than in getReferencedSymbolsSpecial.
            return !options.implementations && isStringLiteral(node) ? getReferencesForStringLiteral(node, sourceFiles, cancellationToken) : undefined;
        }

        if (symbol.escapedName === InternalSymbolName.ExportEquals) {
            return getReferencedSymbolsForModule(program, symbol.parent!, /*excludeImportTypeOfExportEquals*/ false, sourceFiles, sourceFilesSet);
        }

        const moduleReferences = getReferencedSymbolsForModuleIfDeclaredBySourceFile(symbol, program, sourceFiles, cancellationToken, options, sourceFilesSet);
        if (moduleReferences && !(symbol.flags & SymbolFlags.Transient)) {
            return moduleReferences;
        }

        const aliasedSymbol = getMergedAliasedSymbolOfNamespaceExportDeclaration(node, symbol, checker);
        const moduleReferencesOfExportTarget = aliasedSymbol &&
            getReferencedSymbolsForModuleIfDeclaredBySourceFile(aliasedSymbol, program, sourceFiles, cancellationToken, options, sourceFilesSet);

        const references = getReferencedSymbolsForSymbol(symbol, node, sourceFiles, sourceFilesSet, checker, cancellationToken, options);
        return mergeReferences(program, moduleReferences, references, moduleReferencesOfExportTarget);
    }

    function getMergedAliasedSymbolOfNamespaceExportDeclaration(node: Node, symbol: Symbol, checker: TypeChecker) {
        if (node.parent && isNamespaceExportDeclaration(node.parent)) {
            const aliasedSymbol = checker.getAliasedSymbol(symbol);
            const targetSymbol = checker.getMergedSymbol(aliasedSymbol);
            if (aliasedSymbol !== targetSymbol) {
                return targetSymbol;
            }
        }
        return undefined;
    }

    function getReferencedSymbolsForModuleIfDeclaredBySourceFile(symbol: Symbol, program: Program, sourceFiles: ReadonlyArray<SourceFile>, cancellationToken: CancellationToken, options: Options, sourceFilesSet: ReadonlyMap<true>) {
        const moduleSourceFile = symbol.flags & SymbolFlags.Module ? find(symbol.declarations, isSourceFile) : undefined;
        if (!moduleSourceFile) return undefined;
        const exportEquals = symbol.exports!.get(InternalSymbolName.ExportEquals);
        // If !!exportEquals, we're about to add references to `import("mod")` anyway, so don't double-count them.
        const moduleReferences = getReferencedSymbolsForModule(program, symbol, !!exportEquals, sourceFiles, sourceFilesSet);
        if (!exportEquals || !sourceFilesSet.has(moduleSourceFile.fileName)) return moduleReferences;
        // Continue to get references to 'export ='.
        const checker = program.getTypeChecker();
        symbol = skipAlias(exportEquals, checker);
        return mergeReferences(program, moduleReferences, getReferencedSymbolsForSymbol(symbol, /*node*/ undefined, sourceFiles, sourceFilesSet, checker, cancellationToken, options));
    }

    /**
     * Merges the references by sorting them (by file index in sourceFiles and their location in it) that point to same definition symbol
     */
    function mergeReferences(program: Program, ...referencesToMerge: (SymbolAndEntries[] | undefined)[]): SymbolAndEntries[] | undefined {
        let result: SymbolAndEntries[] | undefined;
        for (const references of referencesToMerge) {
            if (!references || !references.length) continue;
            if (!result) {
                result = references;
                continue;
            }
            for (const entry of references) {
                if (!entry.definition || entry.definition.type !== DefinitionKind.Symbol) {
                    result.push(entry);
                    continue;
                }
                const symbol = entry.definition.symbol;
                const refIndex = findIndex(result, ref => !!ref.definition &&
                    ref.definition.type === DefinitionKind.Symbol &&
                    ref.definition.symbol === symbol);
                if (refIndex === -1) {
                    result.push(entry);
                    continue;
                }

                const reference = result[refIndex];
                result[refIndex] = {
                    definition: reference.definition,
                    references: reference.references.concat(entry.references).sort((entry1, entry2) => {
                        const entry1File = getSourceFileIndexOfEntry(program, entry1);
                        const entry2File = getSourceFileIndexOfEntry(program, entry2);
                        if (entry1File !== entry2File) {
                            return compareValues(entry1File, entry2File);
                        }

                        const entry1Span = getTextSpanOfEntry(entry1);
                        const entry2Span = getTextSpanOfEntry(entry2);
                        return entry1Span.start !== entry2Span.start ?
                            compareValues(entry1Span.start, entry2Span.start) :
                            compareValues(entry1Span.length, entry2Span.length);
                    })
                };
            }
        }
        return result;
    }

    function getSourceFileIndexOfEntry(program: Program, entry: Entry) {
        const sourceFile = entry.kind === EntryKind.Span ?
            program.getSourceFile(entry.fileName)! :
            entry.node.getSourceFile();
        return program.getSourceFiles().indexOf(sourceFile);
    }

    function getReferencedSymbolsForModule(program: Program, symbol: Symbol, excludeImportTypeOfExportEquals: boolean, sourceFiles: ReadonlyArray<SourceFile>, sourceFilesSet: ReadonlyMap<true>): SymbolAndEntries[] {
        Debug.assert(!!symbol.valueDeclaration);

        const references = mapDefined<ModuleReference, Entry>(findModuleReferences(program, sourceFiles, symbol), reference => {
            if (reference.kind === "import") {
                const parent = reference.literal.parent;
                if (isLiteralTypeNode(parent)) {
                    const importType = cast(parent.parent, isImportTypeNode);
                    if (excludeImportTypeOfExportEquals && !importType.qualifier) {
                        return undefined;
                    }
                }
                // import("foo") with no qualifier will reference the `export =` of the module, which may be referenced anyway.
                return nodeEntry(reference.literal);
            }
            else {
                return {
                    kind: EntryKind.Span,
                    fileName: reference.referencingFile.fileName,
                    textSpan: createTextSpanFromRange(reference.ref),
                };
            }
        });

        for (const decl of symbol.declarations) {
            switch (decl.kind) {
                case SyntaxKind.SourceFile:
                    // Don't include the source file itself. (This may not be ideal behavior, but awkward to include an entire file as a reference.)
                    break;
                case SyntaxKind.ModuleDeclaration:
                    if (sourceFilesSet.has(decl.getSourceFile().fileName)) {
                        references.push(nodeEntry((decl as ModuleDeclaration).name));
                    }
                    break;
                default:
                    // This may be merged with something.
                    Debug.assert(!!(symbol.flags & SymbolFlags.Transient), "Expected a module symbol to be declared by a SourceFile or ModuleDeclaration.");
            }
        }

        const exported = symbol.exports!.get(InternalSymbolName.ExportEquals);
        if (exported) {
            for (const decl of exported.declarations) {
                const sourceFile = decl.getSourceFile();
                if (sourceFilesSet.has(sourceFile.fileName)) {
                    // At `module.exports = ...`, reference node is `module`
                    const node = isBinaryExpression(decl) && isPropertyAccessExpression(decl.left)
                        ? decl.left.expression
                        : isExportAssignment(decl)
                        ? Debug.assertDefined(findChildOfKind(decl, SyntaxKind.ExportKeyword, sourceFile))
                        : getNameOfDeclaration(decl) || decl;
                    references.push(nodeEntry(node));
                }
            }
        }

        return references.length ? [{ definition: { type: DefinitionKind.Symbol, symbol }, references }] : emptyArray;
    }

    /** getReferencedSymbols for special node kinds. */
    function getReferencedSymbolsSpecial(node: Node, sourceFiles: ReadonlyArray<SourceFile>, cancellationToken: CancellationToken): SymbolAndEntries[] | undefined {
        if (isTypeKeyword(node.kind)) {
            return getAllReferencesForKeyword(sourceFiles, node.kind, cancellationToken);
        }

        // Labels
        if (isJumpStatementTarget(node)) {
            const labelDefinition = getTargetLabel(node.parent, node.text);
            // if we have a label definition, look within its statement for references, if not, then
            // the label is undefined and we have no results..
            return labelDefinition && getLabelReferencesInNode(labelDefinition.parent, labelDefinition);
        }
        else if (isLabelOfLabeledStatement(node)) {
            // it is a label definition and not a target, search within the parent labeledStatement
            return getLabelReferencesInNode(node.parent, node);
        }

        if (isThis(node)) {
            return getReferencesForThisKeyword(node, sourceFiles, cancellationToken);
        }

        if (node.kind === SyntaxKind.SuperKeyword) {
            return getReferencesForSuperKeyword(node);
        }

        return undefined;
    }

    /** Core find-all-references algorithm for a normal symbol. */
    function getReferencedSymbolsForSymbol(originalSymbol: Symbol, node: Node | undefined, sourceFiles: ReadonlyArray<SourceFile>, sourceFilesSet: ReadonlyMap<true>, checker: TypeChecker, cancellationToken: CancellationToken, options: Options): SymbolAndEntries[] {
        const symbol = node && skipPastExportOrImportSpecifierOrUnion(originalSymbol, node, checker, /*useLocalSymbolForExportSpecifier*/ !isForRenameWithPrefixAndSuffixText(options)) || originalSymbol;

        // Compute the meaning from the location and the symbol it references
        const searchMeaning = node ? getIntersectingMeaningFromDeclarations(node, symbol) : SemanticMeaning.All;

        const result: SymbolAndEntries[] = [];
        const state = new State(sourceFiles, sourceFilesSet, node ? getSpecialSearchKind(node) : SpecialSearchKind.None, checker, cancellationToken, searchMeaning, options, result);

        const exportSpecifier = !isForRenameWithPrefixAndSuffixText(options) ? undefined : find(symbol.declarations, isExportSpecifier);
        if (exportSpecifier) {
            // When renaming at an export specifier, rename the export and not the thing being exported.
            getReferencesAtExportSpecifier(exportSpecifier.name, symbol, exportSpecifier, state.createSearch(node, originalSymbol, /*comingFrom*/ undefined), state, /*addReferencesHere*/ true, /*alwaysGetReferences*/ true);
        }
        else if (node && node.kind === SyntaxKind.DefaultKeyword) {
            addReference(node, symbol, state);
            searchForImportsOfExport(node, symbol, { exportingModuleSymbol: Debug.assertDefined(symbol.parent, "Expected export symbol to have a parent"), exportKind: ExportKind.Default }, state);
        }
        else {
            const search = state.createSearch(node, symbol, /*comingFrom*/ undefined, { allSearchSymbols: node ? populateSearchSymbolSet(symbol, node, checker, !!options.isForRename, !!options.providePrefixAndSuffixTextForRename, !!options.implementations) : [symbol] });
            getReferencesInContainerOrFiles(symbol, state, search);
        }

        return result;
    }

    function getReferencesInContainerOrFiles(symbol: Symbol, state: State, search: Search): void {
        // Try to get the smallest valid scope that we can limit our search to;
        // otherwise we'll need to search globally (i.e. include each file).
        const scope = getSymbolScope(symbol);
        if (scope) {
            getReferencesInContainer(scope, scope.getSourceFile(), search, state, /*addReferencesHere*/ !(isSourceFile(scope) && !contains(state.sourceFiles, scope)));
        }
        else {
            // Global search
            for (const sourceFile of state.sourceFiles) {
                state.cancellationToken.throwIfCancellationRequested();
                searchForName(sourceFile, search, state);
            }
        }
    }

    function getSpecialSearchKind(node: Node): SpecialSearchKind {
        switch (node.kind) {
            case SyntaxKind.ConstructorKeyword:
                return SpecialSearchKind.Constructor;
            case SyntaxKind.Identifier:
                if (isClassLike(node.parent)) {
                    Debug.assert(node.parent.name === node);
                    return SpecialSearchKind.Class;
                }
                // falls through
            default:
                return SpecialSearchKind.None;
        }
    }

    /** Handle a few special cases relating to export/import specifiers. */
    function skipPastExportOrImportSpecifierOrUnion(symbol: Symbol, node: Node, checker: TypeChecker, useLocalSymbolForExportSpecifier: boolean): Symbol | undefined {
        const { parent } = node;
        if (isExportSpecifier(parent) && useLocalSymbolForExportSpecifier) {
            return getLocalSymbolForExportSpecifier(node as Identifier, symbol, parent, checker);
        }
        // If the symbol is declared as part of a declaration like `{ type: "a" } | { type: "b" }`, use the property on the union type to get more references.
        return firstDefined(symbol.declarations, decl => {
            if (!decl.parent) {
                // Ignore UMD module and global merge
                if (symbol.flags & SymbolFlags.Transient) return undefined;
                // Assertions for GH#21814. We should be handling SourceFile symbols in `getReferencedSymbolsForModule` instead of getting here.
                Debug.fail(`Unexpected symbol at ${Debug.formatSyntaxKind(node.kind)}: ${Debug.formatSymbol(symbol)}`);
            }
            return isTypeLiteralNode(decl.parent) && isUnionTypeNode(decl.parent.parent)
                ? checker.getPropertyOfType(checker.getTypeFromTypeNode(decl.parent.parent), symbol.name)
                : undefined;
        });
    }

    /**
     * Symbol that is currently being searched for.
     * This will be replaced if we find an alias for the symbol.
     */
    interface Search {
        /** If coming from an export, we will not recursively search for the imported symbol (since that's where we came from). */
        readonly comingFrom?: ImportExport;

        readonly symbol: Symbol;
        readonly text: string;
        readonly escapedText: __String;
        /** Only set if `options.implementations` is true. These are the symbols checked to get the implementations of a property access. */
        readonly parents: ReadonlyArray<Symbol> | undefined;
        readonly allSearchSymbols: ReadonlyArray<Symbol>;

        /**
         * Whether a symbol is in the search set.
         * Do not compare directly to `symbol` because there may be related symbols to search for. See `populateSearchSymbolSet`.
         */
        includes(symbol: Symbol): boolean;
    }

    const enum SpecialSearchKind {
        None,
        Constructor,
        Class,
    }

    function getNonModuleSymbolOfMergedModuleSymbol(symbol: Symbol) {
        if (!(symbol.flags & (SymbolFlags.Module | SymbolFlags.Transient))) return undefined;
        const decl = symbol.declarations && find(symbol.declarations, d => !isSourceFile(d) && !isModuleDeclaration(d));
        return decl && decl.symbol;
    }

    /**
     * Holds all state needed for the finding references.
     * Unlike `Search`, there is only one `State`.
     */
    class State {
        /** Cache for `explicitlyinheritsFrom`. */
        readonly inheritsFromCache = createMap<boolean>();

        /**
         * Type nodes can contain multiple references to the same type. For example:
         *      let x: Foo & (Foo & Bar) = ...
         * Because we are returning the implementation locations and not the identifier locations,
         * duplicate entries would be returned here as each of the type references is part of
         * the same implementation. For that reason, check before we add a new entry.
         */
        readonly markSeenContainingTypeReference = nodeSeenTracker();

        /**
         * It's possible that we will encounter the right side of `export { foo as bar } from "x";` more than once.
         * For example:
         *     // b.ts
         *     export { foo as bar } from "./a";
         *     import { bar } from "./b";
         *
         * Normally at `foo as bar` we directly add `foo` and do not locally search for it (since it doesn't declare a local).
         * But another reference to it may appear in the same source file.
         * See `tests/cases/fourslash/transitiveExportImports3.ts`.
         */
        readonly markSeenReExportRHS = nodeSeenTracker();

        constructor(
            readonly sourceFiles: ReadonlyArray<SourceFile>,
            readonly sourceFilesSet: ReadonlyMap<true>,
            readonly specialSearchKind: SpecialSearchKind,
            readonly checker: TypeChecker,
            readonly cancellationToken: CancellationToken,
            readonly searchMeaning: SemanticMeaning,
            readonly options: Options,
            private readonly result: Push<SymbolAndEntries>) {
        }

        includesSourceFile(sourceFile: SourceFile): boolean {
            return this.sourceFilesSet.has(sourceFile.fileName);
        }

        private importTracker: ImportTracker | undefined;
        /** Gets every place to look for references of an exported symbols. See `ImportsResult` in `importTracker.ts` for more documentation. */
        getImportSearches(exportSymbol: Symbol, exportInfo: ExportInfo): ImportsResult {
            if (!this.importTracker) this.importTracker = createImportTracker(this.sourceFiles, this.sourceFilesSet, this.checker, this.cancellationToken);
            return this.importTracker(exportSymbol, exportInfo, !!this.options.isForRename);
        }

        /** @param allSearchSymbols set of additional symbols for use by `includes`. */
        createSearch(location: Node | undefined, symbol: Symbol, comingFrom: ImportExport | undefined, searchOptions: { text?: string, allSearchSymbols?: Symbol[] } = {}): Search {
            // Note: if this is an external module symbol, the name doesn't include quotes.
            // Note: getLocalSymbolForExportDefault handles `export default class C {}`, but not `export default C` or `export { C as default }`.
            // The other two forms seem to be handled downstream (e.g. in `skipPastExportOrImportSpecifier`), so special-casing the first form
            // here appears to be intentional).
            const {
                text = stripQuotes(unescapeLeadingUnderscores((getLocalSymbolForExportDefault(symbol) || getNonModuleSymbolOfMergedModuleSymbol(symbol) || symbol).escapedName)),
                allSearchSymbols = [symbol],
            } = searchOptions;
            const escapedText = escapeLeadingUnderscores(text);
            const parents = this.options.implementations && location ? getParentSymbolsOfPropertyAccess(location, symbol, this.checker) : undefined;
            return { symbol, comingFrom, text, escapedText, parents, allSearchSymbols, includes: sym => contains(allSearchSymbols, sym) };
        }

        private readonly symbolIdToReferences: Entry[][] = [];
        /**
         * Callback to add references for a particular searched symbol.
         * This initializes a reference group, so only call this if you will add at least one reference.
         */
        referenceAdder(searchSymbol: Symbol): (node: Node, kind?: NodeEntryKind) => void {
            const symbolId = getSymbolId(searchSymbol);
            let references = this.symbolIdToReferences[symbolId];
            if (!references) {
                references = this.symbolIdToReferences[symbolId] = [];
                this.result.push({ definition: { type: DefinitionKind.Symbol, symbol: searchSymbol }, references });
            }
            return (node, kind) => references.push(nodeEntry(node, kind));
        }

        /** Add a reference with no associated definition. */
        addStringOrCommentReference(fileName: string, textSpan: TextSpan): void {
            this.result.push({
                definition: undefined,
                references: [{ kind: EntryKind.Span, fileName, textSpan }]
            });
        }

        // Source file ID → symbol ID → Whether the symbol has been searched for in the source file.
        private readonly sourceFileToSeenSymbols: Map<true>[] = [];
        /** Returns `true` the first time we search for a symbol in a file and `false` afterwards. */
        markSearchedSymbols(sourceFile: SourceFile, symbols: ReadonlyArray<Symbol>): boolean {
            const sourceId = getNodeId(sourceFile);
            const seenSymbols = this.sourceFileToSeenSymbols[sourceId] || (this.sourceFileToSeenSymbols[sourceId] = createMap<true>());

            let anyNewSymbols = false;
            for (const sym of symbols) {
                anyNewSymbols = addToSeen(seenSymbols, getSymbolId(sym)) || anyNewSymbols;
            }
            return anyNewSymbols;
        }
    }

    /** Search for all imports of a given exported symbol using `State.getImportSearches`. */
    function searchForImportsOfExport(exportLocation: Node, exportSymbol: Symbol, exportInfo: ExportInfo, state: State): void {
        const { importSearches, singleReferences, indirectUsers } = state.getImportSearches(exportSymbol, exportInfo);

        // For `import { foo as bar }` just add the reference to `foo`, and don't otherwise search in the file.
        if (singleReferences.length) {
            const addRef = state.referenceAdder(exportSymbol);
            for (const singleRef of singleReferences) {
                if (shouldAddSingleReference(singleRef, state)) addRef(singleRef);
            }
        }

        // For each import, find all references to that import in its source file.
        for (const [importLocation, importSymbol] of importSearches) {
            getReferencesInSourceFile(importLocation.getSourceFile(), state.createSearch(importLocation, importSymbol, ImportExport.Export), state);
        }

        if (indirectUsers.length) {
            let indirectSearch: Search | undefined;
            switch (exportInfo.exportKind) {
                case ExportKind.Named:
                    indirectSearch = state.createSearch(exportLocation, exportSymbol, ImportExport.Export);
                    break;
                case ExportKind.Default:
                    // Search for a property access to '.default'. This can't be renamed.
                    indirectSearch = state.options.isForRename ? undefined : state.createSearch(exportLocation, exportSymbol, ImportExport.Export, { text: "default" });
                    break;
                case ExportKind.ExportEquals:
                    break;
            }
            if (indirectSearch) {
                for (const indirectUser of indirectUsers) {
                    searchForName(indirectUser, indirectSearch, state);
                }
            }
        }
    }

    export function eachExportReference(
        sourceFiles: ReadonlyArray<SourceFile>,
        checker: TypeChecker,
        cancellationToken: CancellationToken | undefined,
        exportSymbol: Symbol,
        exportingModuleSymbol: Symbol,
        exportName: string,
        isDefaultExport: boolean,
        cb: (ref: Identifier) => void,
    ): void {
        const importTracker = createImportTracker(sourceFiles, arrayToSet(sourceFiles, f => f.fileName), checker, cancellationToken);
        const { importSearches, indirectUsers } = importTracker(exportSymbol, { exportKind: isDefaultExport ? ExportKind.Default : ExportKind.Named, exportingModuleSymbol }, /*isForRename*/ false);
        for (const [importLocation] of importSearches) {
            cb(importLocation);
        }
        for (const indirectUser of indirectUsers) {
            for (const node of getPossibleSymbolReferenceNodes(indirectUser, isDefaultExport ? "default" : exportName)) {
                // Import specifiers should be handled by importSearches
                if (isIdentifier(node) && !isImportOrExportSpecifier(node.parent) && checker.getSymbolAtLocation(node) === exportSymbol) {
                    cb(node);
                }
            }
        }
    }

    function shouldAddSingleReference(singleRef: Identifier | StringLiteral, state: State): boolean {
        if (!hasMatchingMeaning(singleRef, state)) return false;
        if (!state.options.isForRename) return true;
        // Don't rename an import type `import("./module-name")` when renaming `name` in `export = name;`
        if (!isIdentifier(singleRef)) return false;
        // At `default` in `import { default as x }` or `export { default as x }`, do add a reference, but do not rename.
        return !(isImportOrExportSpecifier(singleRef.parent) && singleRef.escapedText === InternalSymbolName.Default);
    }

    // Go to the symbol we imported from and find references for it.
    function searchForImportedSymbol(symbol: Symbol, state: State): void {
        for (const declaration of symbol.declarations) {
            const exportingFile = declaration.getSourceFile();
            // Need to search in the file even if it's not in the search-file set, because it might export the symbol.
            getReferencesInSourceFile(exportingFile, state.createSearch(declaration, symbol, ImportExport.Import), state, state.includesSourceFile(exportingFile));
        }
    }

    /** Search for all occurences of an identifier in a source file (and filter out the ones that match). */
    function searchForName(sourceFile: SourceFile, search: Search, state: State): void {
        if (getNameTable(sourceFile).get(search.escapedText) !== undefined) {
            getReferencesInSourceFile(sourceFile, search, state);
        }
    }

    function getPropertySymbolOfDestructuringAssignment(location: Node, checker: TypeChecker): Symbol | undefined {
        return isArrayLiteralOrObjectLiteralDestructuringPattern(location.parent.parent)
            ? checker.getPropertySymbolOfDestructuringAssignment(<Identifier>location)
            : undefined;
    }

    /**
     * Determines the smallest scope in which a symbol may have named references.
     * Note that not every construct has been accounted for. This function can
     * probably be improved.
     *
     * @returns undefined if the scope cannot be determined, implying that
     * a reference to a symbol can occur anywhere.
     */
    function getSymbolScope(symbol: Symbol): Node | undefined {
        // If this is the symbol of a named function expression or named class expression,
        // then named references are limited to its own scope.
        const { declarations, flags, parent, valueDeclaration } = symbol;
        if (valueDeclaration && (valueDeclaration.kind === SyntaxKind.FunctionExpression || valueDeclaration.kind === SyntaxKind.ClassExpression)) {
            return valueDeclaration;
        }

        if (!declarations) {
            return undefined;
        }

        // If this is private property or method, the scope is the containing class
        if (flags & (SymbolFlags.Property | SymbolFlags.Method)) {
            const privateDeclaration = find(declarations, d => hasModifier(d, ModifierFlags.Private));
            if (privateDeclaration) {
                return getAncestor(privateDeclaration, SyntaxKind.ClassDeclaration);
            }
            // Else this is a public property and could be accessed from anywhere.
            return undefined;
        }

        // If symbol is of object binding pattern element without property name we would want to
        // look for property too and that could be anywhere
        if (declarations.some(isObjectBindingElementWithoutPropertyName)) {
            return undefined;
        }

        /*
        If the symbol has a parent, it's globally visible unless:
        - It's a private property (handled above).
        - It's a type parameter.
        - The parent is an external module: then we should only search in the module (and recurse on the export later).
          - But if the parent has `export as namespace`, the symbol is globally visible through that namespace.
        */
        const exposedByParent = parent && !(symbol.flags & SymbolFlags.TypeParameter);
        if (exposedByParent && !(isExternalModuleSymbol(parent!) && !parent!.globalExports)) {
            return undefined;
        }

        let scope: Node | undefined;
        for (const declaration of declarations) {
            const container = getContainerNode(declaration);
            if (scope && scope !== container) {
                // Different declarations have different containers, bail out
                return undefined;
            }

            if (!container || container.kind === SyntaxKind.SourceFile && !isExternalOrCommonJsModule(<SourceFile>container)) {
                // This is a global variable and not an external module, any declaration defined
                // within this scope is visible outside the file
                return undefined;
            }

            // The search scope is the container node
            scope = container;
        }

        // If symbol.parent, this means we are in an export of an external module. (Otherwise we would have returned `undefined` above.)
        // For an export of a module, we may be in a declaration file, and it may be accessed elsewhere. E.g.:
        //     declare module "a" { export type T = number; }
        //     declare module "b" { import { T } from "a"; export const x: T; }
        // So we must search the whole source file. (Because we will mark the source file as seen, we we won't return to it when searching for imports.)
        return exposedByParent ? scope!.getSourceFile() : scope; // TODO: GH#18217
    }

    /** Used as a quick check for whether a symbol is used at all in a file (besides its definition). */
    export function isSymbolReferencedInFile(definition: Identifier, checker: TypeChecker, sourceFile: SourceFile): boolean {
        return eachSymbolReferenceInFile(definition, checker, sourceFile, () => true) || false;
    }

    export function eachSymbolReferenceInFile<T>(definition: Identifier, checker: TypeChecker, sourceFile: SourceFile, cb: (token: Identifier) => T): T | undefined {
        const symbol = isParameterPropertyDeclaration(definition.parent)
            ? first(checker.getSymbolsOfParameterPropertyDeclaration(definition.parent, definition.text))
            : checker.getSymbolAtLocation(definition);
        if (!symbol) return undefined;
        for (const token of getPossibleSymbolReferenceNodes(sourceFile, symbol.name)) {
            if (!isIdentifier(token) || token === definition || token.escapedText !== definition.escapedText) continue;
            const referenceSymbol: Symbol = checker.getSymbolAtLocation(token)!; // See GH#19955 for why the type annotation is necessary
            if (referenceSymbol === symbol
                || checker.getShorthandAssignmentValueSymbol(token.parent) === symbol
                || isExportSpecifier(token.parent) && getLocalSymbolForExportSpecifier(token, referenceSymbol, token.parent, checker) === symbol) {
                const res = cb(token);
                if (res) return res;
            }
        }
    }

    export function eachSignatureCall(signature: SignatureDeclaration, sourceFiles: ReadonlyArray<SourceFile>, checker: TypeChecker, cb: (call: CallExpression) => void): void {
        if (!signature.name || !isIdentifier(signature.name)) return;

        const symbol = Debug.assertDefined(checker.getSymbolAtLocation(signature.name));

        for (const sourceFile of sourceFiles) {
            for (const name of getPossibleSymbolReferenceNodes(sourceFile, symbol.name)) {
                if (!isIdentifier(name) || name === signature.name || name.escapedText !== signature.name.escapedText) continue;
                const called = climbPastPropertyAccess(name);
                const call = called.parent;
                if (!isCallExpression(call) || call.expression !== called) continue;
                const referenceSymbol = checker.getSymbolAtLocation(name);
                if (referenceSymbol && checker.getRootSymbols(referenceSymbol).some(s => s === symbol)) {
                    cb(call);
                }
            }
        }
    }

    function getPossibleSymbolReferenceNodes(sourceFile: SourceFile, symbolName: string, container: Node = sourceFile): ReadonlyArray<Node> {
        return getPossibleSymbolReferencePositions(sourceFile, symbolName, container).map(pos => getTouchingPropertyName(sourceFile, pos));
    }

    function getPossibleSymbolReferencePositions(sourceFile: SourceFile, symbolName: string, container: Node = sourceFile): ReadonlyArray<number> {
        const positions: number[] = [];

        /// TODO: Cache symbol existence for files to save text search
        // Also, need to make this work for unicode escapes.

        // Be resilient in the face of a symbol with no name or zero length name
        if (!symbolName || !symbolName.length) {
            return positions;
        }

        const text = sourceFile.text;
        const sourceLength = text.length;
        const symbolNameLength = symbolName.length;

        let position = text.indexOf(symbolName, container.pos);
        while (position >= 0) {
            // If we are past the end, stop looking
            if (position > container.end) break;

            // We found a match.  Make sure it's not part of a larger word (i.e. the char
            // before and after it have to be a non-identifier char).
            const endPosition = position + symbolNameLength;

            if ((position === 0 || !isIdentifierPart(text.charCodeAt(position - 1), ScriptTarget.Latest)) &&
                (endPosition === sourceLength || !isIdentifierPart(text.charCodeAt(endPosition), ScriptTarget.Latest))) {
                // Found a real match.  Keep searching.
                positions.push(position);
            }
            position = text.indexOf(symbolName, position + symbolNameLength + 1);
        }

        return positions;
    }

    function getLabelReferencesInNode(container: Node, targetLabel: Identifier): SymbolAndEntries[] {
        const sourceFile = container.getSourceFile();
        const labelName = targetLabel.text;
        const references = mapDefined(getPossibleSymbolReferenceNodes(sourceFile, labelName, container), node =>
            // Only pick labels that are either the target label, or have a target that is the target label
            node === targetLabel || (isJumpStatementTarget(node) && getTargetLabel(node, labelName) === targetLabel) ? nodeEntry(node) : undefined);
        return [{ definition: { type: DefinitionKind.Label, node: targetLabel }, references }];
    }

    function isValidReferencePosition(node: Node, searchSymbolName: string): boolean {
        // Compare the length so we filter out strict superstrings of the symbol we are looking for
        switch (node.kind) {
            case SyntaxKind.Identifier:
                return (node as Identifier).text.length === searchSymbolName.length;

            case SyntaxKind.StringLiteral: {
                const str = node as StringLiteral;
                return (isLiteralNameOfPropertyDeclarationOrIndexAccess(str) || isNameOfModuleDeclaration(node) || isExpressionOfExternalModuleImportEqualsDeclaration(node) || (isCallExpression(node.parent) && isBindableObjectDefinePropertyCall(node.parent) && node.parent.arguments[1] === node)) &&
                    str.text.length === searchSymbolName.length;
            }

            case SyntaxKind.NumericLiteral:
                return isLiteralNameOfPropertyDeclarationOrIndexAccess(node as NumericLiteral) && (node as NumericLiteral).text.length === searchSymbolName.length;

            case SyntaxKind.DefaultKeyword:
                return "default".length === searchSymbolName.length;

            default:
                return false;
        }
    }

    function getAllReferencesForKeyword(sourceFiles: ReadonlyArray<SourceFile>, keywordKind: SyntaxKind, cancellationToken: CancellationToken): SymbolAndEntries[] | undefined {
        const references = flatMap(sourceFiles, sourceFile => {
            cancellationToken.throwIfCancellationRequested();
            return mapDefined(getPossibleSymbolReferenceNodes(sourceFile, tokenToString(keywordKind)!, sourceFile), referenceLocation =>
                referenceLocation.kind === keywordKind ? nodeEntry(referenceLocation) : undefined);
        });
        return references.length ? [{ definition: { type: DefinitionKind.Keyword, node: references[0].node }, references }] : undefined;
    }

    function getReferencesInSourceFile(sourceFile: SourceFile, search: Search, state: State, addReferencesHere = true): void {
        state.cancellationToken.throwIfCancellationRequested();
        return getReferencesInContainer(sourceFile, sourceFile, search, state, addReferencesHere);
    }

    /**
     * Search within node "container" for references for a search value, where the search value is defined as a
     * tuple of(searchSymbol, searchText, searchLocation, and searchMeaning).
     * searchLocation: a node where the search value
     */
    function getReferencesInContainer(container: Node, sourceFile: SourceFile, search: Search, state: State, addReferencesHere: boolean): void {
        if (!state.markSearchedSymbols(sourceFile, search.allSearchSymbols)) {
            return;
        }

        for (const position of getPossibleSymbolReferencePositions(sourceFile, search.text, container)) {
            getReferencesAtLocation(sourceFile, position, search, state, addReferencesHere);
        }
    }

    function hasMatchingMeaning(referenceLocation: Node, state: State): boolean {
        return !!(getMeaningFromLocation(referenceLocation) & state.searchMeaning);
    }

    function getReferencesAtLocation(sourceFile: SourceFile, position: number, search: Search, state: State, addReferencesHere: boolean): void {
        const referenceLocation = getTouchingPropertyName(sourceFile, position);

        if (!isValidReferencePosition(referenceLocation, search.text)) {
            // This wasn't the start of a token.  Check to see if it might be a
            // match in a comment or string if that's what the caller is asking
            // for.
            if (!state.options.implementations && (state.options.findInStrings && isInString(sourceFile, position) || state.options.findInComments && isInNonReferenceComment(sourceFile, position))) {
                // In the case where we're looking inside comments/strings, we don't have
                // an actual definition.  So just use 'undefined' here.  Features like
                // 'Rename' won't care (as they ignore the definitions), and features like
                // 'FindReferences' will just filter out these results.
                state.addStringOrCommentReference(sourceFile.fileName, createTextSpan(position, search.text.length));
            }

            return;
        }

        if (!hasMatchingMeaning(referenceLocation, state)) return;

        const referenceSymbol = state.checker.getSymbolAtLocation(referenceLocation);
        if (!referenceSymbol) {
            return;
        }

        const parent = referenceLocation.parent;
        if (isImportSpecifier(parent) && parent.propertyName === referenceLocation) {
            // This is added through `singleReferences` in ImportsResult. If we happen to see it again, don't add it again.
            return;
        }

        if (isExportSpecifier(parent)) {
            Debug.assert(referenceLocation.kind === SyntaxKind.Identifier);
            getReferencesAtExportSpecifier(referenceLocation as Identifier, referenceSymbol, parent, search, state, addReferencesHere);
            return;
        }

        const relatedSymbol = getRelatedSymbol(search, referenceSymbol, referenceLocation, state);
        if (!relatedSymbol) {
            getReferenceForShorthandProperty(referenceSymbol, search, state);
            return;
        }

        switch (state.specialSearchKind) {
            case SpecialSearchKind.None:
                if (addReferencesHere) addReference(referenceLocation, relatedSymbol, state);
                break;
            case SpecialSearchKind.Constructor:
                addConstructorReferences(referenceLocation, sourceFile, search, state);
                break;
            case SpecialSearchKind.Class:
                addClassStaticThisReferences(referenceLocation, search, state);
                break;
            default:
                Debug.assertNever(state.specialSearchKind);
        }

        getImportOrExportReferences(referenceLocation, referenceSymbol, search, state);
    }

    function getReferencesAtExportSpecifier(
        referenceLocation: Identifier,
        referenceSymbol: Symbol,
        exportSpecifier: ExportSpecifier,
        search: Search,
        state: State,
        addReferencesHere: boolean,
        alwaysGetReferences?: boolean,
    ): void {
        Debug.assert(!alwaysGetReferences || !!state.options.providePrefixAndSuffixTextForRename, "If alwaysGetReferences is true, then prefix/suffix text must be enabled");

        const { parent, propertyName, name } = exportSpecifier;
        const exportDeclaration = parent.parent;
        const localSymbol = getLocalSymbolForExportSpecifier(referenceLocation, referenceSymbol, exportSpecifier, state.checker);
        if (!alwaysGetReferences && !search.includes(localSymbol)) {
            return;
        }

        if (!propertyName) {
            // Don't rename at `export { default } from "m";`. (but do continue to search for imports of the re-export)
            if (!(state.options.isForRename && (name.escapedText === InternalSymbolName.Default))) {
                addRef();
            }
        }
        else if (referenceLocation === propertyName) {
            // For `export { foo as bar } from "baz"`, "`foo`" will be added from the singleReferences for import searches of the original export.
            // For `export { foo as bar };`, where `foo` is a local, so add it now.
            if (!exportDeclaration.moduleSpecifier) {
                addRef();
            }

            if (addReferencesHere && !state.options.isForRename && state.markSeenReExportRHS(name)) {
                addReference(name, Debug.assertDefined(exportSpecifier.symbol), state);
            }
        }
        else {
            if (state.markSeenReExportRHS(referenceLocation)) {
                addRef();
            }
        }

        // For `export { foo as bar }`, rename `foo`, but not `bar`.
        if (!isForRenameWithPrefixAndSuffixText(state.options) || alwaysGetReferences) {
            const isDefaultExport = referenceLocation.originalKeywordKind === SyntaxKind.DefaultKeyword
                || exportSpecifier.name.originalKeywordKind === SyntaxKind.DefaultKeyword;
            const exportKind = isDefaultExport ? ExportKind.Default : ExportKind.Named;
            const exportSymbol = Debug.assertDefined(exportSpecifier.symbol);
            const exportInfo = Debug.assertDefined(getExportInfo(exportSymbol, exportKind, state.checker));
            searchForImportsOfExport(referenceLocation, exportSymbol, exportInfo, state);
        }

        // At `export { x } from "foo"`, also search for the imported symbol `"foo".x`.
        if (search.comingFrom !== ImportExport.Export && exportDeclaration.moduleSpecifier && !propertyName && !isForRenameWithPrefixAndSuffixText(state.options)) {
            const imported = state.checker.getExportSpecifierLocalTargetSymbol(exportSpecifier);
            if (imported) searchForImportedSymbol(imported, state);
        }

        function addRef() {
            if (addReferencesHere) addReference(referenceLocation, localSymbol, state);
        }
    }

    function getLocalSymbolForExportSpecifier(referenceLocation: Identifier, referenceSymbol: Symbol, exportSpecifier: ExportSpecifier, checker: TypeChecker): Symbol {
        return isExportSpecifierAlias(referenceLocation, exportSpecifier) && checker.getExportSpecifierLocalTargetSymbol(exportSpecifier) || referenceSymbol;
    }

    function isExportSpecifierAlias(referenceLocation: Identifier, exportSpecifier: ExportSpecifier): boolean {
        const { parent, propertyName, name } = exportSpecifier;
        Debug.assert(propertyName === referenceLocation || name === referenceLocation);
        if (propertyName) {
            // Given `export { foo as bar } [from "someModule"]`: It's an alias at `foo`, but at `bar` it's a new symbol.
            return propertyName === referenceLocation;
        }
        else {
            // `export { foo } from "foo"` is a re-export.
            // `export { foo };` is not a re-export, it creates an alias for the local variable `foo`.
            return !parent.parent.moduleSpecifier;
        }
    }

    function getImportOrExportReferences(referenceLocation: Node, referenceSymbol: Symbol, search: Search, state: State): void {
        const importOrExport = getImportOrExportSymbol(referenceLocation, referenceSymbol, state.checker, search.comingFrom === ImportExport.Export);
        if (!importOrExport) return;

        const { symbol } = importOrExport;

        if (importOrExport.kind === ImportExport.Import) {
            if (!(isForRenameWithPrefixAndSuffixText(state.options))) {
                searchForImportedSymbol(symbol, state);
            }
        }
        else {
            searchForImportsOfExport(referenceLocation, symbol, importOrExport.exportInfo, state);
        }
    }

    function getReferenceForShorthandProperty({ flags, valueDeclaration }: Symbol, search: Search, state: State): void {
        const shorthandValueSymbol = state.checker.getShorthandAssignmentValueSymbol(valueDeclaration)!;
        const name = valueDeclaration && getNameOfDeclaration(valueDeclaration);
        /*
         * Because in short-hand property assignment, an identifier which stored as name of the short-hand property assignment
         * has two meanings: property name and property value. Therefore when we do findAllReference at the position where
         * an identifier is declared, the language service should return the position of the variable declaration as well as
         * the position in short-hand property assignment excluding property accessing. However, if we do findAllReference at the
         * position of property accessing, the referenceEntry of such position will be handled in the first case.
         */
        if (!(flags & SymbolFlags.Transient) && name && search.includes(shorthandValueSymbol)) {
            addReference(name, shorthandValueSymbol, state);
        }
    }

    function addReference(referenceLocation: Node, relatedSymbol: Symbol | RelatedSymbol, state: State): void {
        const { kind, symbol } = "kind" in relatedSymbol ? relatedSymbol : { kind: undefined, symbol: relatedSymbol };
        const addRef = state.referenceAdder(symbol);
        if (state.options.implementations) {
            addImplementationReferences(referenceLocation, addRef, state);
        }
        else {
            addRef(referenceLocation, kind);
        }
    }

    /** Adds references when a constructor is used with `new this()` in its own class and `super()` calls in subclasses.  */
    function addConstructorReferences(referenceLocation: Node, sourceFile: SourceFile, search: Search, state: State): void {
        if (isNewExpressionTarget(referenceLocation)) {
            addReference(referenceLocation, search.symbol, state);
        }

        const pusher = () => state.referenceAdder(search.symbol);

        if (isClassLike(referenceLocation.parent)) {
            Debug.assert(referenceLocation.kind === SyntaxKind.DefaultKeyword || referenceLocation.parent.name === referenceLocation);
            // This is the class declaration containing the constructor.
            findOwnConstructorReferences(search.symbol, sourceFile, pusher());
        }
        else {
            // If this class appears in `extends C`, then the extending class' "super" calls are references.
            const classExtending = tryGetClassByExtendingIdentifier(referenceLocation);
            if (classExtending) {
                findSuperConstructorAccesses(classExtending, pusher());
                findInheritedConstructorReferences(classExtending, state);
            }
        }
    }

    function addClassStaticThisReferences(referenceLocation: Node, search: Search, state: State): void {
        addReference(referenceLocation, search.symbol, state);
        const classLike = referenceLocation.parent;
        if (state.options.isForRename || !isClassLike(classLike)) return;
        Debug.assert(classLike.name === referenceLocation);
        const addRef = state.referenceAdder(search.symbol);
        for (const member of classLike.members) {
            if (!(isMethodOrAccessor(member) && hasModifier(member, ModifierFlags.Static))) {
                continue;
            }
            if (member.body) {
                member.body.forEachChild(function cb(node) {
                    if (node.kind === SyntaxKind.ThisKeyword) {
                        addRef(node);
                    }
                    else if (!isFunctionLike(node) && !isClassLike(node)) {
                        node.forEachChild(cb);
                    }
                });
            }
        }
    }

    /**
     * `classSymbol` is the class where the constructor was defined.
     * Reference the constructor and all calls to `new this()`.
     */
    function findOwnConstructorReferences(classSymbol: Symbol, sourceFile: SourceFile, addNode: (node: Node) => void): void {
        const constructorSymbol = getClassConstructorSymbol(classSymbol);
        if (constructorSymbol) {
            for (const decl of constructorSymbol.declarations) {
                const ctrKeyword = findChildOfKind(decl, SyntaxKind.ConstructorKeyword, sourceFile)!;
                Debug.assert(decl.kind === SyntaxKind.Constructor && !!ctrKeyword);
                addNode(ctrKeyword);
            }
        }

        if (classSymbol.exports) {
            classSymbol.exports.forEach(member => {
                const decl = member.valueDeclaration;
                if (decl && decl.kind === SyntaxKind.MethodDeclaration) {
                    const body = (<MethodDeclaration>decl).body;
                    if (body) {
                        forEachDescendantOfKind(body, SyntaxKind.ThisKeyword, thisKeyword => {
                            if (isNewExpressionTarget(thisKeyword)) {
                                addNode(thisKeyword);
                            }
                        });
                    }
                }
            });
        }
    }

    function getClassConstructorSymbol(classSymbol: Symbol): Symbol | undefined {
        return classSymbol.members && classSymbol.members.get(InternalSymbolName.Constructor);
    }

    /** Find references to `super` in the constructor of an extending class.  */
    function findSuperConstructorAccesses(classDeclaration: ClassLikeDeclaration, addNode: (node: Node) => void): void {
        const constructor = getClassConstructorSymbol(classDeclaration.symbol);
        if (!constructor) {
            return;
        }

        for (const decl of constructor.declarations) {
            Debug.assert(decl.kind === SyntaxKind.Constructor);
            const body = (<ConstructorDeclaration>decl).body;
            if (body) {
                forEachDescendantOfKind(body, SyntaxKind.SuperKeyword, node => {
                    if (isCallExpressionTarget(node)) {
                        addNode(node);
                    }
                });
            }
        }
    }

    function hasOwnConstructor(classDeclaration: ClassLikeDeclaration): boolean {
        return !!getClassConstructorSymbol(classDeclaration.symbol);
    }

    function findInheritedConstructorReferences(classDeclaration: ClassLikeDeclaration, state: State): void {
        if (hasOwnConstructor(classDeclaration)) return;
        const classSymbol = classDeclaration.symbol;
        const search = state.createSearch(/*location*/ undefined, classSymbol, /*comingFrom*/ undefined);
        getReferencesInContainerOrFiles(classSymbol, state, search);
    }

    function addImplementationReferences(refNode: Node, addReference: (node: Node) => void, state: State): void {
        // Check if we found a function/propertyAssignment/method with an implementation or initializer
        if (isDeclarationName(refNode) && isImplementation(refNode.parent)) {
            addReference(refNode);
            return;
        }

        if (refNode.kind !== SyntaxKind.Identifier) {
            return;
        }

        if (refNode.parent.kind === SyntaxKind.ShorthandPropertyAssignment) {
            // Go ahead and dereference the shorthand assignment by going to its definition
            getReferenceEntriesForShorthandPropertyAssignment(refNode, state.checker, addReference);
        }

        // Check if the node is within an extends or implements clause
        const containingClass = getContainingClassIfInHeritageClause(refNode);
        if (containingClass) {
            addReference(containingClass);
            return;
        }

        // If we got a type reference, try and see if the reference applies to any expressions that can implement an interface
        // Find the first node whose parent isn't a type node -- i.e., the highest type node.
        const typeNode = findAncestor(refNode, a => !isQualifiedName(a.parent) && !isTypeNode(a.parent) && !isTypeElement(a.parent))!;
        const typeHavingNode = typeNode.parent;
        if (hasType(typeHavingNode) && typeHavingNode.type === typeNode && state.markSeenContainingTypeReference(typeHavingNode)) {
            if (hasInitializer(typeHavingNode)) {
                addIfImplementation(typeHavingNode.initializer!);
            }
            else if (isFunctionLike(typeHavingNode) && (typeHavingNode as FunctionLikeDeclaration).body) {
                const body = (typeHavingNode as FunctionLikeDeclaration).body!;
                if (body.kind === SyntaxKind.Block) {
                    forEachReturnStatement(<Block>body, returnStatement => {
                        if (returnStatement.expression) addIfImplementation(returnStatement.expression);
                    });
                }
                else {
                    addIfImplementation(body);
                }
            }
            else if (isAssertionExpression(typeHavingNode)) {
                addIfImplementation(typeHavingNode.expression);
            }
        }

        function addIfImplementation(e: Expression): void {
            if (isImplementationExpression(e)) addReference(e);
        }
    }

    function getContainingClassIfInHeritageClause(node: Node): ClassLikeDeclaration | InterfaceDeclaration | undefined {
        return isIdentifier(node) || isPropertyAccessExpression(node) ? getContainingClassIfInHeritageClause(node.parent)
            : isExpressionWithTypeArguments(node) ? tryCast(node.parent.parent, isClassLike) : undefined;
    }

    /**
     * Returns true if this is an expression that can be considered an implementation
     */
    function isImplementationExpression(node: Expression): boolean {
        switch (node.kind) {
            case SyntaxKind.ParenthesizedExpression:
                return isImplementationExpression((<ParenthesizedExpression>node).expression);
            case SyntaxKind.ArrowFunction:
            case SyntaxKind.FunctionExpression:
            case SyntaxKind.ObjectLiteralExpression:
            case SyntaxKind.ClassExpression:
            case SyntaxKind.ArrayLiteralExpression:
                return true;
            default:
                return false;
        }
    }

    /**
     * Determines if the parent symbol occurs somewhere in the child's ancestry. If the parent symbol
     * is an interface, determines if some ancestor of the child symbol extends or inherits from it.
     * Also takes in a cache of previous results which makes this slightly more efficient and is
     * necessary to avoid potential loops like so:
     *     class A extends B { }
     *     class B extends A { }
     *
     * We traverse the AST rather than using the type checker because users are typically only interested
     * in explicit implementations of an interface/class when calling "Go to Implementation". Sibling
     * implementations of types that share a common ancestor with the type whose implementation we are
     * searching for need to be filtered out of the results. The type checker doesn't let us make the
     * distinction between structurally compatible implementations and explicit implementations, so we
     * must use the AST.
     *
     * @param symbol         A class or interface Symbol
     * @param parent        Another class or interface Symbol
     * @param cachedResults A map of symbol id pairs (i.e. "child,parent") to booleans indicating previous results
     */
    function explicitlyInheritsFrom(symbol: Symbol, parent: Symbol, cachedResults: Map<boolean>, checker: TypeChecker): boolean {
        if (symbol === parent) {
            return true;
        }

        const key = getSymbolId(symbol) + "," + getSymbolId(parent);
        const cached = cachedResults.get(key);
        if (cached !== undefined) {
            return cached;
        }

        // Set the key so that we don't infinitely recurse
        cachedResults.set(key, false);

        const inherits = symbol.declarations.some(declaration =>
            getAllSuperTypeNodes(declaration).some(typeReference => {
                const type = checker.getTypeAtLocation(typeReference);
                return !!type && !!type.symbol && explicitlyInheritsFrom(type.symbol, parent, cachedResults, checker);
            }));
        cachedResults.set(key, inherits);
        return inherits;
    }

    function getReferencesForSuperKeyword(superKeyword: Node): SymbolAndEntries[] | undefined {
        let searchSpaceNode = getSuperContainer(superKeyword, /*stopOnFunctions*/ false);
        if (!searchSpaceNode) {
            return undefined;
        }
        // Whether 'super' occurs in a static context within a class.
        let staticFlag = ModifierFlags.Static;

        switch (searchSpaceNode.kind) {
            case SyntaxKind.PropertyDeclaration:
            case SyntaxKind.PropertySignature:
            case SyntaxKind.MethodDeclaration:
            case SyntaxKind.MethodSignature:
            case SyntaxKind.Constructor:
            case SyntaxKind.GetAccessor:
            case SyntaxKind.SetAccessor:
                staticFlag &= getModifierFlags(searchSpaceNode);
                searchSpaceNode = searchSpaceNode.parent; // re-assign to be the owning class
                break;
            default:
                return undefined;
        }

        const sourceFile = searchSpaceNode.getSourceFile();
        const references = mapDefined(getPossibleSymbolReferenceNodes(sourceFile, "super", searchSpaceNode), node => {
            if (node.kind !== SyntaxKind.SuperKeyword) {
                return;
            }

            const container = getSuperContainer(node, /*stopOnFunctions*/ false);

            // If we have a 'super' container, we must have an enclosing class.
            // Now make sure the owning class is the same as the search-space
            // and has the same static qualifier as the original 'super's owner.
            return container && (ModifierFlags.Static & getModifierFlags(container)) === staticFlag && container.parent.symbol === searchSpaceNode.symbol ? nodeEntry(node) : undefined;
        });

        return [{ definition: { type: DefinitionKind.Symbol, symbol: searchSpaceNode.symbol }, references }];
    }

    function isParameterName(node: Node) {
        return node.kind === SyntaxKind.Identifier && node.parent.kind === SyntaxKind.Parameter && (<ParameterDeclaration>node.parent).name === node;
    }

    function getReferencesForThisKeyword(thisOrSuperKeyword: Node, sourceFiles: ReadonlyArray<SourceFile>, cancellationToken: CancellationToken): SymbolAndEntries[] | undefined {
        let searchSpaceNode = getThisContainer(thisOrSuperKeyword, /* includeArrowFunctions */ false);

        // Whether 'this' occurs in a static context within a class.
        let staticFlag = ModifierFlags.Static;

        switch (searchSpaceNode.kind) {
            case SyntaxKind.MethodDeclaration:
            case SyntaxKind.MethodSignature:
                if (isObjectLiteralMethod(searchSpaceNode)) {
                    break;
                }
                // falls through
            case SyntaxKind.PropertyDeclaration:
            case SyntaxKind.PropertySignature:
            case SyntaxKind.Constructor:
            case SyntaxKind.GetAccessor:
            case SyntaxKind.SetAccessor:
                staticFlag &= getModifierFlags(searchSpaceNode);
                searchSpaceNode = searchSpaceNode.parent; // re-assign to be the owning class
                break;
            case SyntaxKind.SourceFile:
                if (isExternalModule(<SourceFile>searchSpaceNode) || isParameterName(thisOrSuperKeyword)) {
                    return undefined;
                }
                // falls through
            case SyntaxKind.FunctionDeclaration:
            case SyntaxKind.FunctionExpression:
                break;
            // Computed properties in classes are not handled here because references to this are illegal,
            // so there is no point finding references to them.
            default:
                return undefined;
        }

        const references = flatMap(searchSpaceNode.kind === SyntaxKind.SourceFile ? sourceFiles : [searchSpaceNode.getSourceFile()], sourceFile => {
            cancellationToken.throwIfCancellationRequested();
            return getPossibleSymbolReferenceNodes(sourceFile, "this", isSourceFile(searchSpaceNode) ? sourceFile : searchSpaceNode).filter(node => {
                if (!isThis(node)) {
                    return false;
                }
                const container = getThisContainer(node, /* includeArrowFunctions */ false);
                switch (searchSpaceNode.kind) {
                    case SyntaxKind.FunctionExpression:
                    case SyntaxKind.FunctionDeclaration:
                        return searchSpaceNode.symbol === container.symbol;
                    case SyntaxKind.MethodDeclaration:
                    case SyntaxKind.MethodSignature:
                        return isObjectLiteralMethod(searchSpaceNode) && searchSpaceNode.symbol === container.symbol;
                    case SyntaxKind.ClassExpression:
                    case SyntaxKind.ClassDeclaration:
                        // Make sure the container belongs to the same class
                        // and has the appropriate static modifier from the original container.
                        return container.parent && searchSpaceNode.symbol === container.parent.symbol && (getModifierFlags(container) & ModifierFlags.Static) === staticFlag;
                    case SyntaxKind.SourceFile:
                        return container.kind === SyntaxKind.SourceFile && !isExternalModule(<SourceFile>container) && !isParameterName(node);
                }
            });
        }).map(n => nodeEntry(n));

        const thisParameter = firstDefined(references, r => isParameter(r.node.parent) ? r.node : undefined);
        return [{
            definition: { type: DefinitionKind.This, node: thisParameter || thisOrSuperKeyword },
            references
        }];
    }

    function getReferencesForStringLiteral(node: StringLiteral, sourceFiles: ReadonlyArray<SourceFile>, cancellationToken: CancellationToken): SymbolAndEntries[] {
        const references = flatMap(sourceFiles, sourceFile => {
            cancellationToken.throwIfCancellationRequested();
            return mapDefined(getPossibleSymbolReferenceNodes(sourceFile, node.text), ref =>
                isStringLiteral(ref) && ref.text === node.text ? nodeEntry(ref, EntryKind.StringLiteral) : undefined);
        });

        return [{
            definition: { type: DefinitionKind.String, node },
            references
        }];
    }

    // For certain symbol kinds, we need to include other symbols in the search set.
    // This is not needed when searching for re-exports.
    function populateSearchSymbolSet(symbol: Symbol, location: Node, checker: TypeChecker, isForRename: boolean, providePrefixAndSuffixText: boolean, implementations: boolean): Symbol[] {
        const result: Symbol[] = [];
        forEachRelatedSymbol<void>(symbol, location, checker, isForRename, !(isForRename && providePrefixAndSuffixText),
            (sym, root, base) => { result.push(base || root || sym); },
            /*allowBaseTypes*/ () => !implementations);
        return result;
    }

    function forEachRelatedSymbol<T>(
        symbol: Symbol, location: Node, checker: TypeChecker, isForRenamePopulateSearchSymbolSet: boolean, onlyIncludeBindingElementAtReferenceLocation: boolean,
        cbSymbol: (symbol: Symbol, rootSymbol?: Symbol, baseSymbol?: Symbol, kind?: NodeEntryKind) => T | undefined,
        allowBaseTypes: (rootSymbol: Symbol) => boolean,
    ): T | undefined {
        const containingObjectLiteralElement = getContainingObjectLiteralElement(location);
        if (containingObjectLiteralElement) {
            /* Because in short-hand property assignment, location has two meaning : property name and as value of the property
             * When we do findAllReference at the position of the short-hand property assignment, we would want to have references to position of
             * property name and variable declaration of the identifier.
             * Like in below example, when querying for all references for an identifier 'name', of the property assignment, the language service
             * should show both 'name' in 'obj' and 'name' in variable declaration
             *      const name = "Foo";
             *      const obj = { name };
             * In order to do that, we will populate the search set with the value symbol of the identifier as a value of the property assignment
             * so that when matching with potential reference symbol, both symbols from property declaration and variable declaration
             * will be included correctly.
             */
            const shorthandValueSymbol = checker.getShorthandAssignmentValueSymbol(location.parent); // gets the local symbol
            if (shorthandValueSymbol && isForRenamePopulateSearchSymbolSet) {
                // When renaming 'x' in `const o = { x }`, just rename the local variable, not the property.
                return cbSymbol(shorthandValueSymbol, /*rootSymbol*/ undefined, /*baseSymbol*/ undefined, EntryKind.SearchedLocalFoundProperty);
            }

            // If the location is in a context sensitive location (i.e. in an object literal) try
            // to get a contextual type for it, and add the property symbol from the contextual
            // type to the search set
            const contextualType = checker.getContextualType(containingObjectLiteralElement.parent);
            const res = contextualType && firstDefined(
                getPropertySymbolsFromContextualType(containingObjectLiteralElement, checker, contextualType, /*unionSymbolOk*/ true),
                sym => fromRoot(sym, EntryKind.SearchedPropertyFoundLocal));
            if (res) return res;

            // If the location is name of property symbol from object literal destructuring pattern
            // Search the property symbol
            //      for ( { property: p2 } of elems) { }
            const propertySymbol = getPropertySymbolOfDestructuringAssignment(location, checker);
            const res1 = propertySymbol && cbSymbol(propertySymbol, /*rootSymbol*/ undefined, /*baseSymbol*/ undefined, EntryKind.SearchedPropertyFoundLocal);
            if (res1) return res1;

            const res2 = shorthandValueSymbol && cbSymbol(shorthandValueSymbol, /*rootSymbol*/ undefined, /*baseSymbol*/ undefined, EntryKind.SearchedLocalFoundProperty);
            if (res2) return res2;
        }

        const aliasedSymbol = getMergedAliasedSymbolOfNamespaceExportDeclaration(location, symbol, checker);
        if (aliasedSymbol) {
            // In case of UMD module and global merging, search for global as well
            const res = cbSymbol(aliasedSymbol, /*rootSymbol*/ undefined, /*baseSymbol*/ undefined, EntryKind.Node);
            if (res) return res;
        }

        const res = fromRoot(symbol);
        if (res) return res;

        if (symbol.valueDeclaration && isParameterPropertyDeclaration(symbol.valueDeclaration)) {
            // For a parameter property, now try on the other symbol (property if this was a parameter, parameter if this was a property).
            const paramProps = checker.getSymbolsOfParameterPropertyDeclaration(cast(symbol.valueDeclaration, isParameter), symbol.name);
            Debug.assert(paramProps.length === 2 && !!(paramProps[0].flags & SymbolFlags.FunctionScopedVariable) && !!(paramProps[1].flags & SymbolFlags.Property)); // is [parameter, property]
            return fromRoot(symbol.flags & SymbolFlags.FunctionScopedVariable ? paramProps[1] : paramProps[0]);
        }

        // symbolAtLocation for a binding element is the local symbol. See if the search symbol is the property.
        // Don't do this when populating search set for a rename when prefix and suffix text will be provided -- just rename the local.
        if (!isForRenamePopulateSearchSymbolSet) {
            let bindingElementPropertySymbol: Symbol | undefined;
            if (onlyIncludeBindingElementAtReferenceLocation) {
                bindingElementPropertySymbol = isObjectBindingElementWithoutPropertyName(location.parent) ? getPropertySymbolFromBindingElement(checker, location.parent) : undefined;
            }
            else {
                bindingElementPropertySymbol = getPropertySymbolOfObjectBindingPatternWithoutPropertyName(symbol, checker);
            }
            return bindingElementPropertySymbol && fromRoot(bindingElementPropertySymbol, EntryKind.SearchedPropertyFoundLocal);
        }

        Debug.assert(isForRenamePopulateSearchSymbolSet);
        // due to the above assert and the arguments at the uses of this function,
        // (onlyIncludeBindingElementAtReferenceLocation <=> !providePrefixAndSuffixTextForRename) holds
        const includeOriginalSymbolOfBindingElement = onlyIncludeBindingElementAtReferenceLocation;

        if (includeOriginalSymbolOfBindingElement) {
            const bindingElementPropertySymbol = getPropertySymbolOfObjectBindingPatternWithoutPropertyName(symbol, checker);
            return bindingElementPropertySymbol && fromRoot(bindingElementPropertySymbol, EntryKind.SearchedPropertyFoundLocal);
        }

        function fromRoot(sym: Symbol, kind?: NodeEntryKind): T | undefined {
            // If this is a union property:
            //   - In populateSearchSymbolsSet we will add all the symbols from all its source symbols in all unioned types.
            //   - In findRelatedSymbol, we will just use the union symbol if any source symbol is included in the search.
            // If the symbol is an instantiation from a another symbol (e.g. widened symbol):
            //   - In populateSearchSymbolsSet, add the root the list
            //   - In findRelatedSymbol, return the source symbol if that is in the search. (Do not return the instantiation symbol.)
            return firstDefined(checker.getRootSymbols(sym), rootSymbol =>
                cbSymbol(sym, rootSymbol, /*baseSymbol*/ undefined, kind)
                // Add symbol of properties/methods of the same name in base classes and implemented interfaces definitions
                || (rootSymbol.parent && rootSymbol.parent.flags & (SymbolFlags.Class | SymbolFlags.Interface) && allowBaseTypes(rootSymbol)
                    ? getPropertySymbolsFromBaseTypes(rootSymbol.parent, rootSymbol.name, checker, base => cbSymbol(sym, rootSymbol, base, kind))
                    : undefined));
        }

        function getPropertySymbolOfObjectBindingPatternWithoutPropertyName(symbol: Symbol, checker: TypeChecker): Symbol | undefined {
            const bindingElement = getDeclarationOfKind<BindingElement>(symbol, SyntaxKind.BindingElement);
            if (bindingElement && isObjectBindingElementWithoutPropertyName(bindingElement)) {
                return getPropertySymbolFromBindingElement(checker, bindingElement);
            }
        }
    }

    interface RelatedSymbol {
        readonly symbol: Symbol;
        readonly kind: NodeEntryKind | undefined;
    }
    function getRelatedSymbol(search: Search, referenceSymbol: Symbol, referenceLocation: Node, state: State): RelatedSymbol | undefined {
        const { checker } = state;
        return forEachRelatedSymbol(referenceSymbol, referenceLocation, checker, /*isForRenamePopulateSearchSymbolSet*/ false,
            /*onlyIncludeBindingElementAtReferenceLocation*/ !state.options.isForRename || !!state.options.providePrefixAndSuffixTextForRename,
            (sym, rootSymbol, baseSymbol, kind): RelatedSymbol | undefined => search.includes(baseSymbol || rootSymbol || sym)
                // For a base type, use the symbol for the derived type. For a synthetic (e.g. union) property, use the union symbol.
                ? { symbol: rootSymbol && !(getCheckFlags(sym) & CheckFlags.Synthetic) ? rootSymbol : sym, kind }
                : undefined,
            /*allowBaseTypes*/ rootSymbol =>
                !(search.parents && !search.parents.some(parent => explicitlyInheritsFrom(rootSymbol.parent!, parent, state.inheritsFromCache, checker))));
    }

    /**
     * Given an initial searchMeaning, extracted from a location, widen the search scope based on the declarations
     * of the corresponding symbol. e.g. if we are searching for "Foo" in value position, but "Foo" references a class
     * then we need to widen the search to include type positions as well.
     * On the contrary, if we are searching for "Bar" in type position and we trace bar to an interface, and an uninstantiated
     * module, we want to keep the search limited to only types, as the two declarations (interface and uninstantiated module)
     * do not intersect in any of the three spaces.
     */
    export function getIntersectingMeaningFromDeclarations(node: Node, symbol: Symbol): SemanticMeaning {
        let meaning = getMeaningFromLocation(node);
        const { declarations } = symbol;
        if (declarations) {
            let lastIterationMeaning: SemanticMeaning;
            do {
                // The result is order-sensitive, for instance if initialMeaning === Namespace, and declarations = [class, instantiated module]
                // we need to consider both as they initialMeaning intersects with the module in the namespace space, and the module
                // intersects with the class in the value space.
                // To achieve that we will keep iterating until the result stabilizes.

                // Remember the last meaning
                lastIterationMeaning = meaning;

                for (const declaration of declarations) {
                    const declarationMeaning = getMeaningFromDeclaration(declaration);

                    if (declarationMeaning & meaning) {
                        meaning |= declarationMeaning;
                    }
                }
            }
            while (meaning !== lastIterationMeaning);
        }
        return meaning;
    }

    function isImplementation(node: Node): boolean {
        return !!(node.flags & NodeFlags.Ambient)
            ? !(isInterfaceDeclaration(node) || isTypeAliasDeclaration(node))
            : (isVariableLike(node) ? hasInitializer(node)
                : isFunctionLikeDeclaration(node) ? !!node.body
                : isClassLike(node) || isModuleOrEnumDeclaration(node));
    }

    export function getReferenceEntriesForShorthandPropertyAssignment(node: Node, checker: TypeChecker, addReference: (node: Node) => void): void {
        const refSymbol = checker.getSymbolAtLocation(node)!;
        const shorthandSymbol = checker.getShorthandAssignmentValueSymbol(refSymbol.valueDeclaration);

        if (shorthandSymbol) {
            for (const declaration of shorthandSymbol.getDeclarations()!) {
                if (getMeaningFromDeclaration(declaration) & SemanticMeaning.Value) {
                    addReference(declaration);
                }
            }
        }
    }

    function forEachDescendantOfKind(node: Node, kind: SyntaxKind, action: (node: Node) => void): void {
        forEachChild(node, child => {
            if (child.kind === kind) {
                action(child);
            }
            forEachDescendantOfKind(child, kind, action);
        });
    }

    /** Get `C` given `N` if `N` is in the position `class C extends N` or `class C extends foo.N` where `N` is an identifier. */
    function tryGetClassByExtendingIdentifier(node: Node): ClassLikeDeclaration | undefined {
        return tryGetClassExtendingExpressionWithTypeArguments(climbPastPropertyAccess(node).parent);
    }

    /**
     * If we are just looking for implementations and this is a property access expression, we need to get the
     * symbol of the local type of the symbol the property is being accessed on. This is because our search
     * symbol may have a different parent symbol if the local type's symbol does not declare the property
     * being accessed (i.e. it is declared in some parent class or interface)
     */
    function getParentSymbolsOfPropertyAccess(location: Node, symbol: Symbol, checker: TypeChecker): ReadonlyArray<Symbol> | undefined {
        const propertyAccessExpression = isRightSideOfPropertyAccess(location) ? <PropertyAccessExpression>location.parent : undefined;
        const lhsType = propertyAccessExpression && checker.getTypeAtLocation(propertyAccessExpression.expression);
        const res = mapDefined(lhsType && (lhsType.isUnionOrIntersection() ? lhsType.types : lhsType.symbol === symbol.parent ? undefined : [lhsType]), t =>
            t.symbol && t.symbol.flags & (SymbolFlags.Class | SymbolFlags.Interface) ? t.symbol : undefined);
        return res.length === 0 ? undefined : res;
    }

    function isForRenameWithPrefixAndSuffixText(options: Options) {
        return options.isForRename && options.providePrefixAndSuffixTextForRename;
    }
}