Add inline variable refactor (#54281)

src/compiler/diagnosticMessages.json

@@ -7632,6 +7632,18 @@
         "category": "Message",
         "code": 95183
     },
+    "Inline variable": {
+        "category": "Message",
+        "code": 95184
+    },
+    "Could not find variable to inline.": {
+        "category": "Message",
+        "code": 95185
+    },
+    "Variables with multiple declarations cannot be inlined.": {
+        "category": "Message",
+        "code": 95186
+    },
 
     "No value exists in scope for the shorthand property '{0}'. Either declare one or provide an initializer.": {
         "category": "Error",

src/services/_namespaces/ts.refactor.ts

@@ -5,6 +5,7 @@ export * from "../refactors/convertExport";
 export * from "../refactors/convertImport";
 export * from "../refactors/extractType";
 export * from "../refactors/helpers";
+export * from "../refactors/inlineVariable";
 export * from "../refactors/moveToNewFile";
 export * from "../refactors/moveToFile";
 import * as addOrRemoveBracesToArrowFunction from "./ts.refactor.addOrRemoveBracesToArrowFunction";

src/services/findAllReferences.ts

@@ -849,8 +849,12 @@ export function getTextSpanOfEntry(entry: Entry) {
         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 {
+/**
+ * A node is considered a writeAccess iff it is a name of a declaration or a target of an assignment.
+ *
+ * @internal
+ */
+export function isWriteAccessForReference(node: Node): boolean {
     const decl = getDeclarationFromName(node);
     return !!decl && declarationIsWriteAccess(decl) || node.kind === SyntaxKind.DefaultKeyword || isWriteAccess(node);
 }

src/services/refactors/inlineVariable.ts

@@ -0,0 +1,236 @@
+import {
+    cast,
+    Debug,
+    Diagnostics,
+    emptyArray,
+    Expression,
+    factory,
+    FindAllReferences,
+    getExpressionPrecedence,
+    getLocaleSpecificMessage,
+    getSynthesizedDeepClone,
+    getTouchingPropertyName,
+    Identifier,
+    InitializedVariableDeclaration,
+    isCallLikeExpression,
+    isExportAssignment,
+    isExportModifier,
+    isExportSpecifier,
+    isExpression,
+    isFunctionLike,
+    isIdentifier,
+    isInitializedVariable,
+    isTypeQueryNode,
+    isVariableDeclarationInVariableStatement,
+    isVariableStatement,
+    needsParentheses,
+    Node,
+    Program,
+    refactor,
+    some,
+    SourceFile,
+    SymbolFlags,
+    textChanges,
+    textRangeContainsPositionInclusive,
+    TypeChecker,
+    VariableDeclaration,
+} from "../_namespaces/ts";
+import { RefactorErrorInfo, registerRefactor } from "../_namespaces/ts.refactor";
+
+const refactorName = "Inline variable";
+const refactorDescription = getLocaleSpecificMessage(Diagnostics.Inline_variable);
+
+const inlineVariableAction = {
+    name: refactorName,
+    description: refactorDescription,
+    kind: "refactor.inline.variable"
+};
+
+interface InliningInfo {
+    references: Node[];
+    declaration: VariableDeclaration;
+    replacement: Expression;
+}
+
+registerRefactor(refactorName, {
+    kinds: [inlineVariableAction.kind],
+
+    getAvailableActions(context) {
+        const {
+            file,
+            program,
+            preferences,
+            startPosition,
+            triggerReason
+        } = context;
+
+        // tryWithReferenceToken is true below when triggerReason === "invoked", since we want to
+        // always provide the refactor in the declaration site but only show it in references when
+        // the refactor is explicitly invoked.
+        const info = getInliningInfo(file, startPosition, triggerReason === "invoked", program);
+        if (!info) {
+            return emptyArray;
+        }
+
+        if (!refactor.isRefactorErrorInfo(info)) {
+            return [{
+                name: refactorName,
+                description: refactorDescription,
+                actions: [inlineVariableAction]
+            }];
+        }
+
+        if (preferences.provideRefactorNotApplicableReason) {
+            return [{
+                name: refactorName,
+                description: refactorDescription,
+                actions: [{
+                    ...inlineVariableAction,
+                    notApplicableReason: info.error
+                }]
+            }];
+        }
+
+        return emptyArray;
+    },
+
+    getEditsForAction(context, actionName) {
+        Debug.assert(actionName === refactorName, "Unexpected refactor invoked");
+
+        const { file, program, startPosition } = context;
+
+        // tryWithReferenceToken is true below since here we're already performing the refactor.
+        // The trigger kind was only relevant when checking the availability of the refactor.
+        const info = getInliningInfo(file, startPosition, /*tryWithReferenceToken*/ true, program);
+        if (!info || refactor.isRefactorErrorInfo(info)) {
+            return undefined;
+        }
+
+        const { references, declaration, replacement } = info;
+        const edits = textChanges.ChangeTracker.with(context, tracker => {
+            for (const node of references) {
+                tracker.replaceNode(file, node, getReplacementExpression(node, replacement));
+            }
+            tracker.delete(file, declaration);
+        });
+
+        return { edits };
+    }
+});
+
+function getInliningInfo(file: SourceFile, startPosition: number, tryWithReferenceToken: boolean, program: Program): InliningInfo | RefactorErrorInfo | undefined {
+    const checker = program.getTypeChecker();
+    const token = getTouchingPropertyName(file, startPosition);
+    const parent = token.parent;
+
+    if (!isIdentifier(token)) {
+        return undefined;
+    }
+
+    // If triggered in a variable declaration, make sure it's not in a catch clause or for-loop
+    // and that it has a value.
+    if (isInitializedVariable(parent) && isVariableDeclarationInVariableStatement(parent)) {
+        // Don't inline the variable if it has multiple declarations.
+        if (checker.getMergedSymbol(parent.symbol).declarations?.length !== 1) {
+            return { error: getLocaleSpecificMessage(Diagnostics.Variables_with_multiple_declarations_cannot_be_inlined) };
+        }
+
+        // Do not inline if the variable is exported.
+        if (isDeclarationExported(parent)) {
+            return undefined;
+        }
+
+        // Find all references to the variable in the current file.
+        const references = getReferenceNodes(parent, checker, file);
+        return references && { references, declaration: parent, replacement: parent.initializer };
+    }
+
+    // Try finding the declaration and nodes to replace via the reference token.
+    if (tryWithReferenceToken) {
+        let definition = checker.resolveName(token.text, token, SymbolFlags.Value, /*excludeGlobals*/ false);
+        definition = definition && checker.getMergedSymbol(definition);
+
+        // Don't inline the variable if it has multiple declarations.
+        if (definition?.declarations?.length !== 1) {
+            return { error: getLocaleSpecificMessage(Diagnostics.Variables_with_multiple_declarations_cannot_be_inlined) };
+        }
+
+        // Make sure we're not inlining something like "let foo;" or "for (let i = 0; i < 5; i++) {}".
+        const declaration = definition.declarations[0];
+        if (!isInitializedVariable(declaration) || !isVariableDeclarationInVariableStatement(declaration) || !isIdentifier(declaration.name)) {
+            return undefined;
+        }
+
+        // Do not inline if the variable is exported.
+        if (isDeclarationExported(declaration)) {
+            return undefined;
+        }
+
+        const references = getReferenceNodes(declaration, checker, file);
+        return references && { references, declaration, replacement: declaration.initializer };
+    }
+
+    return { error: getLocaleSpecificMessage(Diagnostics.Could_not_find_variable_to_inline) };
+}
+
+function isDeclarationExported(declaration: InitializedVariableDeclaration): boolean {
+    // We use this function after isVariableDeclarationInVariableStatement, which ensures
+    // that the cast below succeeds.
+    const variableStatement = cast(declaration.parent.parent, isVariableStatement);
+    return some(variableStatement.modifiers, isExportModifier);
+}
+
+function getReferenceNodes(declaration: InitializedVariableDeclaration, checker: TypeChecker, file: SourceFile): Identifier[] | undefined {
+    const references: Identifier[] = [];
+    const cannotInline = FindAllReferences.Core.eachSymbolReferenceInFile(declaration.name as Identifier, checker, file, ref => {
+        // Only inline if all references are reads. Else we might end up with an invalid scenario like:
+        // const y = x++ + 1 -> const y = 2++ + 1
+        if (FindAllReferences.isWriteAccessForReference(ref)) {
+            return true;
+        }
+
+        // We cannot inline exported variables like "export { x as y }" or "export default foo".
+        if (isExportSpecifier(ref.parent) || isExportAssignment(ref.parent)) {
+            return true;
+        }
+
+        // typeof needs an identifier, so we can't inline a value in there.
+        if (isTypeQueryNode(ref.parent)) {
+            return true;
+        }
+
+        // Cannot inline recursive declarations (e.g. const foo = () => foo();)
+        if (textRangeContainsPositionInclusive(declaration, ref.pos)) {
+            return true;
+        }
+
+        references.push(ref);
+    });
+
+    return references.length === 0 || cannotInline ? undefined : references;
+}
+
+function getReplacementExpression(reference: Node, replacement: Expression): Expression {
+    // Make sure each reference site gets its own copy of the replacement node.
+    replacement = getSynthesizedDeepClone(replacement);
+    const { parent } = reference;
+
+    // Logic from binaryOperandNeedsParentheses: "If the operand has lower precedence,
+    // then it needs to be parenthesized to preserve the intent of the expression.
+    // If the operand has higher precedence, then it does not need to be parenthesized."
+    //
+    // Note that binaryOperandNeedsParentheses has further logic when the precedences
+    // are equal, but for the purposes of this refactor we keep things simple and
+    // instead just check for special cases with needsParentheses.
+    if (isExpression(parent) && (getExpressionPrecedence(replacement) < getExpressionPrecedence(parent) || needsParentheses(parent))) {
+        return factory.createParenthesizedExpression(replacement);
+    }
+
+    // Functions also need to be parenthesized.
+    // E.g.: const f = () => {}; f(); -> (() => {})();
+    if (isFunctionLike(replacement) && isCallLikeExpression(parent)) {
+        return factory.createParenthesizedExpression(replacement);
+    }
+
+    return replacement;
+}