[WIP] Improve optional chaining checker performance (#33794)

* Improve optional chaining checker performance

* Improve optional chaining checker performance

* Add flags to Signature

* Inline getOptionalExpression

* split checks for optional chains

* Cache optional call signatures

src/compiler/binder.ts

@@ -953,7 +953,7 @@ namespace ts {
             }
             if (expression.kind === SyntaxKind.TrueKeyword && flags & FlowFlags.FalseCondition ||
                 expression.kind === SyntaxKind.FalseKeyword && flags & FlowFlags.TrueCondition) {
-                if (!isOptionalChainRoot(expression.parent)) {
+                if (!isExpressionOfOptionalChainRoot(expression)) {
                     return unreachableFlow;
                 }
             }

src/compiler/checker.ts

@@ -327,10 +327,6 @@ namespace ts {
         /** This will be set during calls to `getResolvedSignature` where services determines an apparent number of arguments greater than what is actually provided. */
         let apparentArgumentCount: number | undefined;
 
-        // This object is reused for `checkOptionalExpression` return values to avoid frequent GC due to nursery object allocations.
-        // This object represents a pool-size of 1.
-        const pooledOptionalTypeResult: { isOptional: boolean, type: Type } = { isOptional: false, type: undefined! };
-
         // for public members that accept a Node or one of its subtypes, we must guard against
         // synthetic nodes created during transformations by calling `getParseTreeNode`.
         // for most of these, we perform the guard only on `checker` to avoid any possible
@@ -712,10 +708,10 @@ namespace ts {
 
         const noTypePredicate = createTypePredicate(TypePredicateKind.Identifier, "<<unresolved>>", 0, anyType);
 
-        const anySignature = createSignature(undefined, undefined, undefined, emptyArray, anyType, /*resolvedTypePredicate*/ undefined, 0, /*hasRestParameter*/ false, /*hasLiteralTypes*/ false);
-        const unknownSignature = createSignature(undefined, undefined, undefined, emptyArray, errorType, /*resolvedTypePredicate*/ undefined, 0, /*hasRestParameter*/ false, /*hasLiteralTypes*/ false);
-        const resolvingSignature = createSignature(undefined, undefined, undefined, emptyArray, anyType, /*resolvedTypePredicate*/ undefined, 0, /*hasRestParameter*/ false, /*hasLiteralTypes*/ false);
-        const silentNeverSignature = createSignature(undefined, undefined, undefined, emptyArray, silentNeverType, /*resolvedTypePredicate*/ undefined, 0, /*hasRestParameter*/ false, /*hasLiteralTypes*/ false);
+        const anySignature = createSignature(undefined, undefined, undefined, emptyArray, anyType, /*resolvedTypePredicate*/ undefined, 0, SignatureFlags.None);
+        const unknownSignature = createSignature(undefined, undefined, undefined, emptyArray, errorType, /*resolvedTypePredicate*/ undefined, 0, SignatureFlags.None);
+        const resolvingSignature = createSignature(undefined, undefined, undefined, emptyArray, anyType, /*resolvedTypePredicate*/ undefined, 0, SignatureFlags.None);
+        const silentNeverSignature = createSignature(undefined, undefined, undefined, emptyArray, silentNeverType, /*resolvedTypePredicate*/ undefined, 0, SignatureFlags.None);
 
         const enumNumberIndexInfo = createIndexInfo(stringType, /*isReadonly*/ true);
 
@@ -7721,7 +7717,7 @@ namespace ts {
             const signatures = getSignaturesOfType(type, SignatureKind.Construct);
             if (signatures.length === 1) {
                 const s = signatures[0];
-                return !s.typeParameters && s.parameters.length === 1 && s.hasRestParameter && getElementTypeOfArrayType(getTypeOfParameter(s.parameters[0])) === anyType;
+                return !s.typeParameters && s.parameters.length === 1 && signatureHasRestParameter(s) && getElementTypeOfArrayType(getTypeOfParameter(s.parameters[0])) === anyType;
             }
             return false;
         }
@@ -8612,10 +8608,9 @@ namespace ts {
             resolvedReturnType: Type | undefined,
             resolvedTypePredicate: TypePredicate | undefined,
             minArgumentCount: number,
-            hasRestParameter: boolean,
-            hasLiteralTypes: boolean,
+            flags: SignatureFlags
         ): Signature {
-            const sig = new Signature(checker);
+            const sig = new Signature(checker, flags);
             sig.declaration = declaration;
             sig.typeParameters = typeParameters;
             sig.parameters = parameters;
@@ -8623,8 +8618,6 @@ namespace ts {
             sig.resolvedReturnType = resolvedReturnType;
             sig.resolvedTypePredicate = resolvedTypePredicate;
             sig.minArgumentCount = minArgumentCount;
-            sig.hasRestParameter = hasRestParameter;
-            sig.hasLiteralTypes = hasLiteralTypes;
             sig.target = undefined;
             sig.mapper = undefined;
             return sig;
@@ -8632,7 +8625,7 @@ namespace ts {
 
         function cloneSignature(sig: Signature): Signature {
             const result = createSignature(sig.declaration, sig.typeParameters, sig.thisParameter, sig.parameters, /*resolvedReturnType*/ undefined,
-                /*resolvedTypePredicate*/ undefined, sig.minArgumentCount, sig.hasRestParameter, sig.hasLiteralTypes);
+                /*resolvedTypePredicate*/ undefined, sig.minArgumentCount, sig.flags & SignatureFlags.PropagatingFlags);
             result.target = sig.target;
             result.mapper = sig.mapper;
             return result;
@@ -8646,14 +8639,19 @@ namespace ts {
             return result;
         }
 
+        function getOptionalCallSignature(signature: Signature) {
+            return signatureIsOptionalCall(signature) ? signature :
+                (signature.optionalCallSignatureCache || (signature.optionalCallSignatureCache = createOptionalCallSignature(signature)));
+        }
+
         function createOptionalCallSignature(signature: Signature) {
             const result = cloneSignature(signature);
-            result.isOptionalCall = true;
+            result.flags |= SignatureFlags.IsOptionalCall;
             return result;
         }
 
         function getExpandedParameters(sig: Signature): readonly Symbol[] {
-            if (sig.hasRestParameter) {
+            if (signatureHasRestParameter(sig)) {
                 const restIndex = sig.parameters.length - 1;
                 const restParameter = sig.parameters[restIndex];
                 const restType = getTypeOfSymbol(restParameter);
@@ -8679,7 +8677,7 @@ namespace ts {
             const baseConstructorType = getBaseConstructorTypeOfClass(classType);
             const baseSignatures = getSignaturesOfType(baseConstructorType, SignatureKind.Construct);
             if (baseSignatures.length === 0) {
-                return [createSignature(undefined, classType.localTypeParameters, undefined, emptyArray, classType, /*resolvedTypePredicate*/ undefined, 0, /*hasRestParameter*/ false, /*hasLiteralTypes*/ false)];
+                return [createSignature(undefined, classType.localTypeParameters, undefined, emptyArray, classType, /*resolvedTypePredicate*/ undefined, 0, SignatureFlags.None)];
             }
             const baseTypeNode = getBaseTypeNodeOfClass(classType)!;
             const isJavaScript = isInJSFile(baseTypeNode);
@@ -8843,8 +8841,6 @@ namespace ts {
             const params = combineUnionParameters(left, right);
             const thisParam = combineUnionThisParam(left.thisParameter, right.thisParameter);
             const minArgCount = Math.max(left.minArgumentCount, right.minArgumentCount);
-            const hasRestParam = left.hasRestParameter || right.hasRestParameter;
-            const hasLiteralTypes = left.hasLiteralTypes || right.hasLiteralTypes;
             const result = createSignature(
                 declaration,
                 left.typeParameters || right.typeParameters,
@@ -8853,8 +8849,7 @@ namespace ts {
                 /*resolvedReturnType*/ undefined,
                 /*resolvedTypePredicate*/ undefined,
                 minArgCount,
-                hasRestParam,
-                hasLiteralTypes
+                (left.flags | right.flags) & SignatureFlags.PropagatingFlags
             );
             result.unionSignatures = concatenate(left.unionSignatures || [left], [right]);
             return result;
@@ -9036,7 +9031,7 @@ namespace ts {
                         constructSignatures = addRange(constructSignatures.slice(), mapDefined(
                             type.callSignatures,
                             sig => isJSConstructor(sig.declaration) ?
-                                createSignature(sig.declaration, sig.typeParameters, sig.thisParameter, sig.parameters, classType, /*resolvedTypePredicate*/ undefined, sig.minArgumentCount, sig.hasRestParameter, sig.hasLiteralTypes) :
+                                createSignature(sig.declaration, sig.typeParameters, sig.thisParameter, sig.parameters, classType, /*resolvedTypePredicate*/ undefined, sig.minArgumentCount, sig.flags & SignatureFlags.PropagatingFlags) :
                                 undefined));
                     }
                     if (!constructSignatures.length) {
@@ -10043,7 +10038,7 @@ namespace ts {
             const links = getNodeLinks(declaration);
             if (!links.resolvedSignature) {
                 const parameters: Symbol[] = [];
-                let hasLiteralTypes = false;
+                let flags = SignatureFlags.None;
                 let minArgumentCount = 0;
                 let thisParameter: Symbol | undefined;
                 let hasThisParameter = false;
@@ -10077,7 +10072,7 @@ namespace ts {
                     }
 
                     if (type && type.kind === SyntaxKind.LiteralType) {
-                        hasLiteralTypes = true;
+                        flags |= SignatureFlags.HasLiteralTypes;
                     }
 
                     // Record a new minimum argument count if this is not an optional parameter
@@ -10106,10 +10101,12 @@ namespace ts {
                     getDeclaredTypeOfClassOrInterface(getMergedSymbol((<ClassDeclaration>declaration.parent).symbol))
                     : undefined;
                 const typeParameters = classType ? classType.localTypeParameters : getTypeParametersFromDeclaration(declaration);
-                const hasRestLikeParameter = hasRestParameter(declaration) || isInJSFile(declaration) && maybeAddJsSyntheticRestParameter(declaration, parameters);
+                if (hasRestParameter(declaration) || isInJSFile(declaration) && maybeAddJsSyntheticRestParameter(declaration, parameters)) {
+                    flags |= SignatureFlags.HasRestParameter;
+                }
                 links.resolvedSignature = createSignature(declaration, typeParameters, thisParameter, parameters,
                     /*resolvedReturnType*/ undefined, /*resolvedTypePredicate*/ undefined,
-                    minArgumentCount, hasRestLikeParameter, hasLiteralTypes);
+                    minArgumentCount, flags);
             }
             return links.resolvedSignature;
         }
@@ -10264,8 +10261,8 @@ namespace ts {
                     signature.unionSignatures ? getUnionType(map(signature.unionSignatures, getReturnTypeOfSignature), UnionReduction.Subtype) :
                     getReturnTypeFromAnnotation(signature.declaration!) ||
                     (nodeIsMissing((<FunctionLikeDeclaration>signature.declaration).body) ? anyType : getReturnTypeFromBody(<FunctionLikeDeclaration>signature.declaration));
-                if (signature.isOptionalCall) {
-                    type = propagateOptionalTypeMarker(type, /*wasOptional*/ true);
+                if (signatureIsOptionalCall(signature)) {
+                    type = addOptionalTypeMarker(type);
                 }
                 if (!popTypeResolution()) {
                     if (signature.declaration) {
@@ -10325,7 +10322,7 @@ namespace ts {
         }
 
         function tryGetRestTypeOfSignature(signature: Signature): Type | undefined {
-            if (signature.hasRestParameter) {
+            if (signatureHasRestParameter(signature)) {
                 const sigRestType = getTypeOfSymbol(signature.parameters[signature.parameters.length - 1]);
                 const restType = isTupleType(sigRestType) ? getRestTypeOfTupleType(sigRestType) : sigRestType;
                 return restType && getIndexTypeOfType(restType, IndexKind.Number);
@@ -12907,8 +12904,7 @@ namespace ts {
                 /*resolvedReturnType*/ undefined,
                 /*resolvedTypePredicate*/ undefined,
                 signature.minArgumentCount,
-                signature.hasRestParameter,
-                signature.hasLiteralTypes);
+                signature.flags & SignatureFlags.PropagatingFlags);
             result.target = signature;
             result.mapper = mapper;
             return result;
@@ -13861,7 +13857,7 @@ namespace ts {
          */
         function isAnySignature(s: Signature) {
             return !s.typeParameters && (!s.thisParameter || isTypeAny(getTypeOfParameter(s.thisParameter))) && s.parameters.length === 1 &&
-                s.hasRestParameter && (getTypeOfParameter(s.parameters[0]) === anyArrayType || isTypeAny(getTypeOfParameter(s.parameters[0]))) &&
+                signatureHasRestParameter(s) && (getTypeOfParameter(s.parameters[0]) === anyArrayType || isTypeAny(getTypeOfParameter(s.parameters[0]))) &&
                 isTypeAny(getReturnTypeOfSignature(s));
         }
 
@@ -16686,48 +16682,22 @@ namespace ts {
             return strictNullChecks ? getUnionType([type, optionalType]) : type;
         }
 
+        function isNotOptionalTypeMarker(type: Type) {
+            return type !== optionalType;
+        }
+
         function removeOptionalTypeMarker(type: Type): Type {
-            return strictNullChecks ? filterType(type, t => t !== optionalType) : type;
+            return strictNullChecks ? filterType(type, isNotOptionalTypeMarker) : type;
         }
 
         function propagateOptionalTypeMarker(type: Type, wasOptional: boolean) {
             return wasOptional ? addOptionalTypeMarker(type) : type;
         }
 
-        function createPooledOptionalTypeResult(isOptional: boolean, type: Type) {
-            pooledOptionalTypeResult.isOptional = isOptional;
-            pooledOptionalTypeResult.type = type;
-            return pooledOptionalTypeResult;
-        }
-
-        function checkOptionalExpression(
-            parent: PropertyAccessExpression | QualifiedName | ElementAccessExpression | CallExpression,
-            expression: Expression | QualifiedName,
-            nullDiagnostic?: DiagnosticMessage,
-            undefinedDiagnostic?: DiagnosticMessage,
-            nullOrUndefinedDiagnostic?: DiagnosticMessage,
-        ) {
-            let isOptional = false;
-            let type = checkExpression(expression);
-            if (isOptionalChain(parent)) {
-                if (parent.questionDotToken) {
-                    // If we have a questionDotToken then we are an OptionalExpression and should remove `null` and
-                    // `undefined` from the type and add the optionalType to the result, if needed.
-                    isOptional = isNullableType(type);
-                    return createPooledOptionalTypeResult(isOptional, isOptional ? getNonNullableType(type) : type);
-                }
-
-                // If we do not have a questionDotToken, then we are an OptionalChain and we remove the optionalType and
-                // indicate whether we need to add optionalType back into the result.
-                const nonOptionalType = removeOptionalTypeMarker(type);
-                if (nonOptionalType !== type) {
-                    isOptional = true;
-                    type = nonOptionalType;
-                }
-            }
-
-            type = checkNonNullType(type, expression, nullDiagnostic, undefinedDiagnostic, nullOrUndefinedDiagnostic);
-            return createPooledOptionalTypeResult(isOptional, type);
+        function getOptionalExpressionType(exprType: Type, expression: Expression) {
+            return isExpressionOfOptionalChainRoot(expression) ? getNonNullableType(exprType) :
+                isOptionalChain(expression) ? removeOptionalTypeMarker(exprType) :
+                exprType;
         }
 
         /**
@@ -18771,9 +18741,21 @@ namespace ts {
                 // expressions are potential type predicate function calls. In order to avoid triggering
                 // circularities in control flow analysis, we use getTypeOfDottedName when resolving the call
                 // target expression of an assertion.
-                const funcType = node.parent.kind === SyntaxKind.ExpressionStatement ? getTypeOfDottedName(node.expression, /*diagnostic*/ undefined) :
-                    node.expression.kind !== SyntaxKind.SuperKeyword ? checkOptionalExpression(node, node.expression).type :
-                    undefined;
+                let funcType: Type | undefined;
+                if (node.parent.kind === SyntaxKind.ExpressionStatement) {
+                    funcType = getTypeOfDottedName(node.expression, /*diagnostic*/ undefined);
+                }
+                else if (node.expression.kind !== SyntaxKind.SuperKeyword) {
+                    if (isOptionalChain(node)) {
+                        funcType = checkNonNullType(
+                            getOptionalExpressionType(checkExpression(node.expression), node.expression),
+                            node.expression
+                        );
+                    }
+                    else {
+                        funcType = checkNonNullExpression(node.expression);
+                    }
+                }
                 const signatures = getSignaturesOfType(funcType && getApparentType(funcType) || unknownType, SignatureKind.Call);
                 const candidate = signatures.length === 1 && !signatures[0].typeParameters ? signatures[0] :
                     some(signatures, hasTypePredicateOrNeverReturnType) ? getResolvedSignature(node) :
@@ -19780,7 +19762,7 @@ namespace ts {
             // will be a subtype or the same type as the argument.
             function narrowType(type: Type, expr: Expression, assumeTrue: boolean): Type {
                 // for `a?.b`, we emulate a synthetic `a !== null && a !== undefined` condition for `a`
-                if (isOptionalChainRoot(expr.parent) ||
+                if (isExpressionOfOptionalChainRoot(expr) ||
                     isBinaryExpression(expr.parent) && expr.parent.operatorToken.kind === SyntaxKind.QuestionQuestionToken && expr.parent.left === expr) {
                     return narrowTypeByOptionality(type, expr, assumeTrue);
                 }
@@ -22682,19 +22664,8 @@ namespace ts {
             return !!forEachProperty(symbol, prop => !(prop.flags & SymbolFlags.Method));
         }
 
-        function checkNonNullExpression(
-            node: Expression | QualifiedName,
-            nullDiagnostic?: DiagnosticMessage,
-            undefinedDiagnostic?: DiagnosticMessage,
-            nullOrUndefinedDiagnostic?: DiagnosticMessage,
-        ) {
-            return checkNonNullType(
-                checkExpression(node),
-                node,
-                nullDiagnostic,
-                undefinedDiagnostic,
-                nullOrUndefinedDiagnostic
-            );
+        function checkNonNullExpression(node: Expression | QualifiedName) {
+            return checkNonNullType(checkExpression(node), node);
         }
 
         function isNullableType(type: Type) {
@@ -22705,12 +22676,26 @@ namespace ts {
             return isNullableType(type) ? getNonNullableType(type) : type;
         }
 
-        function checkNonNullType(
+        function reportObjectPossiblyNullOrUndefinedError(node: Node, flags: TypeFlags) {
+            error(node, flags & TypeFlags.Undefined ? flags & TypeFlags.Null ?
+                Diagnostics.Object_is_possibly_null_or_undefined :
+                Diagnostics.Object_is_possibly_undefined :
+                Diagnostics.Object_is_possibly_null
+            );
+        }
+
+        function reportCannotInvokePossiblyNullOrUndefinedError(node: Node, flags: TypeFlags) {
+            error(node, flags & TypeFlags.Undefined ? flags & TypeFlags.Null ?
+                Diagnostics.Cannot_invoke_an_object_which_is_possibly_null_or_undefined :
+                Diagnostics.Cannot_invoke_an_object_which_is_possibly_undefined :
+                Diagnostics.Cannot_invoke_an_object_which_is_possibly_null
+            );
+        }
+
+        function checkNonNullTypeWithReporter(
             type: Type,
             node: Node,
-            nullDiagnostic?: DiagnosticMessage,
-            undefinedDiagnostic?: DiagnosticMessage,
-            nullOrUndefinedDiagnostic?: DiagnosticMessage
+            reportError: (node: Node, kind: TypeFlags) => void
         ): Type {
             if (strictNullChecks && type.flags & TypeFlags.Unknown) {
                 error(node, Diagnostics.Object_is_of_type_unknown);
@@ -22718,17 +22703,17 @@ namespace ts {
             }
             const kind = (strictNullChecks ? getFalsyFlags(type) : type.flags) & TypeFlags.Nullable;
             if (kind) {
-                error(node, kind & TypeFlags.Undefined ? kind & TypeFlags.Null ?
-                    (nullOrUndefinedDiagnostic || Diagnostics.Object_is_possibly_null_or_undefined) :
-                    (undefinedDiagnostic || Diagnostics.Object_is_possibly_undefined) :
-                    (nullDiagnostic || Diagnostics.Object_is_possibly_null)
-                );
+                reportError(node, kind);
                 const t = getNonNullableType(type);
                 return t.flags & (TypeFlags.Nullable | TypeFlags.Never) ? errorType : t;
             }
             return type;
         }
 
+        function checkNonNullType(type: Type, node: Node) {
+            return checkNonNullTypeWithReporter(type, node, reportObjectPossiblyNullOrUndefinedError);
+        }
+
         function checkNonNullNonVoidType(type: Type, node: Node): Type {
             const nonNullType = checkNonNullType(type, node);
             if (nonNullType !== errorType && nonNullType.flags & TypeFlags.Void) {
@@ -22738,11 +22723,18 @@ namespace ts {
         }
 
         function checkPropertyAccessExpression(node: PropertyAccessExpression) {
-            return checkPropertyAccessExpressionOrQualifiedName(node, node.expression, node.name);
+            return node.flags & NodeFlags.OptionalChain ? checkPropertyAccessChain(node as PropertyAccessChain) :
+                checkPropertyAccessExpressionOrQualifiedName(node, node.expression, checkNonNullExpression(node.expression), node.name);
+        }
+
+        function checkPropertyAccessChain(node: PropertyAccessChain) {
+            const leftType = checkExpression(node.expression);
+            const nonOptionalType = getOptionalExpressionType(leftType, node.expression);
+            return propagateOptionalTypeMarker(checkPropertyAccessExpressionOrQualifiedName(node, node.expression, checkNonNullType(nonOptionalType, node.expression), node.name), nonOptionalType !== leftType);
         }
 
         function checkQualifiedName(node: QualifiedName) {
-            return checkPropertyAccessExpressionOrQualifiedName(node, node.left, node.right);
+            return checkPropertyAccessExpressionOrQualifiedName(node, node.left, checkNonNullExpression(node.left), node.right);
         }
 
         function isMethodAccessForCall(node: Node) {
@@ -22752,8 +22744,7 @@ namespace ts {
             return isCallOrNewExpression(node.parent) && node.parent.expression === node;
         }
 
-        function checkPropertyAccessExpressionOrQualifiedName(node: PropertyAccessExpression | QualifiedName, left: Expression | QualifiedName, right: Identifier) {
-            const { isOptional, type: leftType } = checkOptionalExpression(node, left);
+        function checkPropertyAccessExpressionOrQualifiedName(node: PropertyAccessExpression | QualifiedName, left: Expression | QualifiedName, leftType: Type, right: Identifier) {
             const parentSymbol = getNodeLinks(left).resolvedSymbol;
             const assignmentKind = getAssignmentTargetKind(node);
             const apparentType = getApparentType(assignmentKind !== AssignmentKind.None || isMethodAccessForCall(node) ? getWidenedType(leftType) : leftType);
@@ -22807,7 +22798,7 @@ namespace ts {
                 }
                 propType = getConstraintForLocation(getTypeOfSymbol(prop), node);
             }
-            return propagateOptionalTypeMarker(getFlowTypeOfAccessExpression(node, prop, propType, right), isOptional);
+            return getFlowTypeOfAccessExpression(node, prop, propType, right);
         }
 
         function getFlowTypeOfAccessExpression(node: ElementAccessExpression | PropertyAccessExpression | QualifiedName, prop: Symbol | undefined, propType: Type, errorNode: Node) {
@@ -23164,7 +23155,17 @@ namespace ts {
         }
 
         function checkIndexedAccess(node: ElementAccessExpression): Type {
-            const { isOptional, type: exprType } = checkOptionalExpression(node, node.expression);
+            return node.flags & NodeFlags.OptionalChain ? checkElementAccessChain(node as ElementAccessChain) :
+                checkElementAccessExpression(node, checkNonNullExpression(node.expression));
+        }
+
+        function checkElementAccessChain(node: ElementAccessChain) {
+            const exprType = checkExpression(node.expression);
+            const nonOptionalType = getOptionalExpressionType(exprType, node.expression);
+            return propagateOptionalTypeMarker(checkElementAccessExpression(node, checkNonNullType(nonOptionalType, node.expression)), nonOptionalType !== exprType);
+        }
+
+        function checkElementAccessExpression(node: ElementAccessExpression, exprType: Type): Type {
             const objectType = getAssignmentTargetKind(node) !== AssignmentKind.None || isMethodAccessForCall(node) ? getWidenedType(exprType) : exprType;
             const indexExpression = node.argumentExpression;
             const indexType = checkExpression(indexExpression);
@@ -23183,7 +23184,7 @@ namespace ts {
                 AccessFlags.Writing | (isGenericObjectType(objectType) && !isThisTypeParameter(objectType) ? AccessFlags.NoIndexSignatures : 0) :
                 AccessFlags.None;
             const indexedAccessType = getIndexedAccessTypeOrUndefined(objectType, effectiveIndexType, node, accessFlags) || errorType;
-            return propagateOptionalTypeMarker(checkIndexedAccessIndexType(getFlowTypeOfAccessExpression(node, indexedAccessType.symbol, indexedAccessType, indexExpression), node), isOptional);
+            return checkIndexedAccessIndexType(getFlowTypeOfAccessExpression(node, indexedAccessType.symbol, indexedAccessType, indexExpression), node);
         }
 
         function checkThatExpressionIsProperSymbolReference(expression: Expression, expressionType: Type, reportError: boolean): boolean {
@@ -23296,7 +23297,7 @@ namespace ts {
 
                 // specialized signatures always need to be placed before non-specialized signatures regardless
                 // of the cutoff position; see GH#1133
-                if (signature.hasLiteralTypes) {
+                if (signatureHasLiteralTypes(signature)) {
                     specializedIndex++;
                     spliceIndex = specializedIndex;
                     // The cutoff index always needs to be greater than or equal to the specialized signature index
@@ -23308,7 +23309,7 @@ namespace ts {
                     spliceIndex = index;
                 }
 
-                result.splice(spliceIndex, 0, isOptionalCall ? createOptionalCallSignature(signature) : signature);
+                result.splice(spliceIndex, 0, isOptionalCall ? getOptionalCallSignature(signature) : signature);
             }
         }
 
@@ -24266,17 +24267,21 @@ namespace ts {
             const { min: minArgumentCount, max: maxNonRestParam } = minAndMax(candidates, getNumNonRestParameters);
             const parameters: Symbol[] = [];
             for (let i = 0; i < maxNonRestParam; i++) {
-                const symbols = mapDefined(candidates, ({ parameters, hasRestParameter }) => hasRestParameter ?
-                    i < parameters.length - 1 ? parameters[i] : last(parameters) :
-                    i < parameters.length ? parameters[i] : undefined);
+                const symbols = mapDefined(candidates, s => signatureHasRestParameter(s) ?
+                    i < s.parameters.length - 1 ? s.parameters[i] : last(s.parameters) :
+                    i < s.parameters.length ? s.parameters[i] : undefined);
                 Debug.assert(symbols.length !== 0);
                 parameters.push(createCombinedSymbolFromTypes(symbols, mapDefined(candidates, candidate => tryGetTypeAtPosition(candidate, i))));
             }
-            const restParameterSymbols = mapDefined(candidates, c => c.hasRestParameter ? last(c.parameters) : undefined);
-            const hasRestParameter = restParameterSymbols.length !== 0;
-            if (hasRestParameter) {
+            const restParameterSymbols = mapDefined(candidates, c => signatureHasRestParameter(c) ? last(c.parameters) : undefined);
+            let flags = SignatureFlags.None;
+            if (restParameterSymbols.length !== 0) {
                 const type = createArrayType(getUnionType(mapDefined(candidates, tryGetRestTypeOfSignature), UnionReduction.Subtype));
                 parameters.push(createCombinedSymbolForOverloadFailure(restParameterSymbols, type));
+                flags |= SignatureFlags.HasRestParameter;
+            }
+            if (candidates.some(signatureHasLiteralTypes)) {
+                flags |= SignatureFlags.HasLiteralTypes;
             }
             return createSignature(
                 candidates[0].declaration,
@@ -24286,13 +24291,12 @@ namespace ts {
                 /*resolvedReturnType*/ getIntersectionType(candidates.map(getReturnTypeOfSignature)),
                 /*typePredicate*/ undefined,
                 minArgumentCount,
-                hasRestParameter,
-                /*hasLiteralTypes*/ candidates.some(c => c.hasLiteralTypes));
+                flags);
         }
 
         function getNumNonRestParameters(signature: Signature): number {
             const numParams = signature.parameters.length;
-            return signature.hasRestParameter ? numParams - 1 : numParams;
+            return signatureHasRestParameter(signature) ? numParams - 1 : numParams;
         }
 
         function createCombinedSymbolFromTypes(sources: readonly Symbol[], types: Type[]): Symbol {
@@ -24383,12 +24387,20 @@ namespace ts {
                 return resolveUntypedCall(node);
             }
 
-            const { isOptional, type: funcType } = checkOptionalExpression(
-                node,
+            let isOptional: boolean;
+            let funcType = checkExpression(node.expression);
+            if (isCallChain(node)) {
+                const nonOptionalType = getOptionalExpressionType(funcType, node.expression);
+                isOptional = nonOptionalType !== funcType;
+                funcType = nonOptionalType;
+            }
+            else {
+                isOptional = false;
+            }
+            funcType = checkNonNullTypeWithReporter(
+                funcType,
                 node.expression,
-                Diagnostics.Cannot_invoke_an_object_which_is_possibly_null,
-                Diagnostics.Cannot_invoke_an_object_which_is_possibly_undefined,
-                Diagnostics.Cannot_invoke_an_object_which_is_possibly_null_or_undefined
+                reportCannotInvokePossiblyNullOrUndefinedError
             );
 
             if (funcType === silentNeverType) {
@@ -24842,8 +24854,7 @@ namespace ts {
                 typeSymbol ? getDeclaredTypeOfSymbol(typeSymbol) : errorType,
                 /*returnTypePredicate*/ undefined,
                 1,
-                /*hasRestparameter*/ false,
-                /*hasLiteralTypes*/ false
+                SignatureFlags.None
             );
         }
 
@@ -24882,7 +24893,7 @@ namespace ts {
         function isPotentiallyUncalledDecorator(decorator: Decorator, signatures: readonly Signature[]) {
             return signatures.length && every(signatures, signature =>
                 signature.minArgumentCount === 0 &&
-                !signature.hasRestParameter &&
+                !signatureHasRestParameter(signature) &&
                 signature.parameters.length < getDecoratorArgumentCount(decorator, signature));
         }
 
@@ -25298,7 +25309,7 @@ namespace ts {
         }
 
         function getParameterNameAtPosition(signature: Signature, pos: number) {
-            const paramCount = signature.parameters.length - (signature.hasRestParameter ? 1 : 0);
+            const paramCount = signature.parameters.length - (signatureHasRestParameter(signature) ? 1 : 0);
             if (pos < paramCount) {
                 return signature.parameters[pos].escapedName;
             }
@@ -25317,11 +25328,11 @@ namespace ts {
         }
 
         function tryGetTypeAtPosition(signature: Signature, pos: number): Type | undefined {
-            const paramCount = signature.parameters.length - (signature.hasRestParameter ? 1 : 0);
+            const paramCount = signature.parameters.length - (signatureHasRestParameter(signature) ? 1 : 0);
             if (pos < paramCount) {
                 return getTypeOfParameter(signature.parameters[pos]);
             }
-            if (signature.hasRestParameter) {
+            if (signatureHasRestParameter(signature)) {
                 // We want to return the value undefined for an out of bounds parameter position,
                 // so we need to check bounds here before calling getIndexedAccessType (which
                 // otherwise would return the type 'undefined').
@@ -25358,7 +25369,7 @@ namespace ts {
 
         function getParameterCount(signature: Signature) {
             const length = signature.parameters.length;
-            if (signature.hasRestParameter) {
+            if (signatureHasRestParameter(signature)) {
                 const restType = getTypeOfSymbol(signature.parameters[length - 1]);
                 if (isTupleType(restType)) {
                     return length + getTypeArguments(restType).length - 1;
@@ -25368,7 +25379,7 @@ namespace ts {
         }
 
         function getMinArgumentCount(signature: Signature) {
-            if (signature.hasRestParameter) {
+            if (signatureHasRestParameter(signature)) {
                 const restType = getTypeOfSymbol(signature.parameters[signature.parameters.length - 1]);
                 if (isTupleType(restType)) {
                     const minLength = restType.target.minLength;
@@ -25381,7 +25392,7 @@ namespace ts {
         }
 
         function hasEffectiveRestParameter(signature: Signature) {
-            if (signature.hasRestParameter) {
+            if (signatureHasRestParameter(signature)) {
                 const restType = getTypeOfSymbol(signature.parameters[signature.parameters.length - 1]);
                 return !isTupleType(restType) || restType.target.hasRestElement;
             }
@@ -25389,7 +25400,7 @@ namespace ts {
         }
 
         function getEffectiveRestType(signature: Signature) {
-            if (signature.hasRestParameter) {
+            if (signatureHasRestParameter(signature)) {
                 const restType = getTypeOfSymbol(signature.parameters[signature.parameters.length - 1]);
                 return isTupleType(restType) ? getRestArrayTypeOfTupleType(restType) : restType;
             }
@@ -25410,7 +25421,7 @@ namespace ts {
         }
 
         function inferFromAnnotatedParameters(signature: Signature, context: Signature, inferenceContext: InferenceContext) {
-            const len = signature.parameters.length - (signature.hasRestParameter ? 1 : 0);
+            const len = signature.parameters.length - (signatureHasRestParameter(signature) ? 1 : 0);
             for (let i = 0; i < len; i++) {
                 const declaration = <ParameterDeclaration>signature.parameters[i].valueDeclaration;
                 if (declaration.type) {
@@ -25444,7 +25455,7 @@ namespace ts {
                     assignTypeToParameterAndFixTypeParameters(signature.thisParameter!, getTypeOfSymbol(context.thisParameter));
                 }
             }
-            const len = signature.parameters.length - (signature.hasRestParameter ? 1 : 0);
+            const len = signature.parameters.length - (signatureHasRestParameter(signature) ? 1 : 0);
             for (let i = 0; i < len; i++) {
                 const parameter = signature.parameters[i];
                 if (!getEffectiveTypeAnnotationNode(<ParameterDeclaration>parameter.valueDeclaration)) {
@@ -25452,7 +25463,7 @@ namespace ts {
                     assignTypeToParameterAndFixTypeParameters(parameter, contextualParameterType);
                 }
             }
-            if (signature.hasRestParameter) {
+            if (signatureHasRestParameter(signature)) {
                 // parameter might be a transient symbol generated by use of `arguments` in the function body.
                 const parameter = last(signature.parameters);
                 if (isTransientSymbol(parameter) || !getEffectiveTypeAnnotationNode(<ParameterDeclaration>parameter.valueDeclaration)) {
@@ -25890,7 +25901,7 @@ namespace ts {
                         return links.contextFreeType;
                     }
                     const returnType = getReturnTypeFromBody(node, checkMode);
-                    const returnOnlySignature = createSignature(undefined, undefined, undefined, emptyArray, returnType, /*resolvedTypePredicate*/ undefined, 0, /*hasRestParameter*/ false, /*hasLiteralTypes*/ false);
+                    const returnOnlySignature = createSignature(undefined, undefined, undefined, emptyArray, returnType, /*resolvedTypePredicate*/ undefined, 0, SignatureFlags.None);
                     const returnOnlyType = createAnonymousType(node.symbol, emptySymbols, [returnOnlySignature], emptyArray, undefined, undefined);
                     returnOnlyType.objectFlags |= ObjectFlags.NonInferrableType;
                     return links.contextFreeType = returnOnlyType;
@@ -27355,7 +27366,18 @@ namespace ts {
             // Optimize for the common case of a call to a function with a single non-generic call
             // signature where we can just fetch the return type without checking the arguments.
             if (isCallExpression(expr) && expr.expression.kind !== SyntaxKind.SuperKeyword && !isRequireCall(expr, /*checkArgumentIsStringLiteralLike*/ true) && !isSymbolOrSymbolForCall(expr)) {
-                const { isOptional, type: funcType } = checkOptionalExpression(expr, expr.expression);
+                let isOptional: boolean;
+                let funcType: Type;
+                if (isCallChain(expr)) {
+                    funcType = checkExpression(expr.expression);
+                    const nonOptionalType = getOptionalExpressionType(funcType, expr.expression);
+                    isOptional = funcType !== nonOptionalType;
+                    funcType = checkNonNullType(nonOptionalType, expr.expression);
+                }
+                else {
+                    isOptional = false;
+                    funcType = checkNonNullExpression(expr.expression);
+                }
                 const signature = getSingleCallSignature(funcType);
                 if (signature && !signature.typeParameters) {
                     return propagateOptionalTypeMarker(getReturnTypeOfSignature(signature), isOptional);
@@ -27630,7 +27652,7 @@ namespace ts {
             }
             else {
                 if (typePredicate.parameterIndex >= 0) {
-                    if (signature.hasRestParameter && typePredicate.parameterIndex === signature.parameters.length - 1) {
+                    if (signatureHasRestParameter(signature) && typePredicate.parameterIndex === signature.parameters.length - 1) {
                         error(parameterName, Diagnostics.A_type_predicate_cannot_reference_a_rest_parameter);
                     }
                     else {
@@ -36062,4 +36084,16 @@ namespace ts {
             case IterationTypeKind.Next: return "nextType";
         }
     }
+
+    export function signatureHasRestParameter(s: Signature) {
+        return !!(s.flags & SignatureFlags.HasRestParameter);
+    }
+
+    export function signatureHasLiteralTypes(s: Signature) {
+        return !!(s.flags & SignatureFlags.HasLiteralTypes);
+    }
+
+    export function signatureIsOptionalCall(s: Signature) {
+        return !!(s.flags & SignatureFlags.IsOptionalCall);
+    }
 }

src/compiler/types.ts

@@ -3451,8 +3451,7 @@ namespace ts {
             resolvedReturnType: Type,
             typePredicate: TypePredicate | undefined,
             minArgumentCount: number,
-            hasRestParameter: boolean,
-            hasLiteralTypes: boolean,
+            flags: SignatureFlags
         ): Signature;
         /* @internal */ createSymbol(flags: SymbolFlags, name: __String): TransientSymbol;
         /* @internal */ createIndexInfo(type: Type, isReadonly: boolean, declaration?: SignatureDeclaration): IndexInfo;
@@ -4671,7 +4670,22 @@ namespace ts {
         Construct,
     }
 
+    /* @internal */
+    export const enum SignatureFlags {
+        None = 0,
+        HasRestParameter = 1 << 0,      // Indicates last parameter is rest parameter
+        HasLiteralTypes = 1 << 1,       // Indicates signature is specialized
+        IsOptionalCall = 1 << 2,        // Indicates signature comes from a CallChain
+
+        // We do not propagate `IsOptionalCall` to instantiated signatures, as that would result in us
+        // attempting to add `| undefined` on each recursive call to `getReturnTypeOfSignature` when
+        // instantiating the return type.
+        PropagatingFlags = HasRestParameter | HasLiteralTypes,
+    }
+
     export interface Signature {
+        /* @internal */ flags: SignatureFlags;
+        /* @internal */ checker?: TypeChecker;
         declaration?: SignatureDeclaration | JSDocSignature; // Originating declaration
         typeParameters?: readonly TypeParameter[];   // Type parameters (undefined if non-generic)
         parameters: readonly Symbol[];               // Parameters
@@ -4688,10 +4702,6 @@ namespace ts {
         /* @internal */
         minArgumentCount: number;           // Number of non-optional parameters
         /* @internal */
-        hasRestParameter: boolean;          // True if last parameter is rest parameter
-        /* @internal */
-        hasLiteralTypes: boolean;           // True if specialized
-        /* @internal */
         target?: Signature;                 // Instantiation target
         /* @internal */
         mapper?: TypeMapper;                // Instantiation mapper
@@ -4702,11 +4712,11 @@ namespace ts {
         /* @internal */
         canonicalSignatureCache?: Signature; // Canonical version of signature (deferred)
         /* @internal */
+        optionalCallSignatureCache?: Signature; // Optional chained call version of signature (deferred)
+        /* @internal */
         isolatedSignatureType?: ObjectType; // A manufactured type that just contains the signature for purposes of signature comparison
         /* @internal */
         instantiations?: Map<Signature>;    // Generic signature instantiation cache
-        /* @internal */
-        isOptionalCall?: boolean;
     }
 
     export const enum IndexKind {

src/compiler/utilities.ts

@@ -5911,6 +5911,14 @@ namespace ts {
                 || kind === SyntaxKind.CallExpression);
     }
 
+    /**
+     * Determines whether a node is the expression preceding an optional chain (i.e. `a` in `a?.b`).
+     */
+    /* @internal */
+    export function isExpressionOfOptionalChainRoot(node: Node): node is Expression & { parent: OptionalChainRoot } {
+        return isOptionalChainRoot(node.parent) && node.parent.expression === node;
+    }
+
     export function isNewExpression(node: Node): node is NewExpression {
         return node.kind === SyntaxKind.NewExpression;
     }
@@ -7310,7 +7318,7 @@ namespace ts {
         getSourceFileConstructor(): new (kind: SyntaxKind.SourceFile, pos?: number, end?: number) => SourceFile;
         getSymbolConstructor(): new (flags: SymbolFlags, name: __String) => Symbol;
         getTypeConstructor(): new (checker: TypeChecker, flags: TypeFlags) => Type;
-        getSignatureConstructor(): new (checker: TypeChecker) => Signature;
+        getSignatureConstructor(): new (checker: TypeChecker, flags: SignatureFlags) => Signature;
         getSourceMapSourceConstructor(): new (fileName: string, text: string, skipTrivia?: (pos: number) => number) => SourceMapSource;
     }
 
@@ -7331,7 +7339,12 @@ namespace ts {
         }
     }
 
-    function Signature() {}
+    function Signature(this: Signature, checker: TypeChecker, flags: SignatureFlags) {
+        this.flags = flags;
+        if (Debug.isDebugging) {
+            this.checker = checker;
+        }
+    }
 
     function Node(this: Node, kind: SyntaxKind, pos: number, end: number) {
         this.pos = pos;

src/services/codefixes/helpers.ts

@@ -233,14 +233,14 @@ namespace ts.codefix {
         let someSigHasRestParameter = false;
         for (const sig of signatures) {
             minArgumentCount = Math.min(sig.minArgumentCount, minArgumentCount);
-            if (sig.hasRestParameter) {
+            if (signatureHasRestParameter(sig)) {
                 someSigHasRestParameter = true;
             }
-            if (sig.parameters.length >= maxArgsSignature.parameters.length && (!sig.hasRestParameter || maxArgsSignature.hasRestParameter)) {
+            if (sig.parameters.length >= maxArgsSignature.parameters.length && (!signatureHasRestParameter(sig) || signatureHasRestParameter(maxArgsSignature))) {
                 maxArgsSignature = sig;
             }
         }
-        const maxNonRestArgs = maxArgsSignature.parameters.length - (maxArgsSignature.hasRestParameter ? 1 : 0);
+        const maxNonRestArgs = maxArgsSignature.parameters.length - (signatureHasRestParameter(maxArgsSignature) ? 1 : 0);
         const maxArgsParameterSymbolNames = maxArgsSignature.parameters.map(symbol => symbol.name);
 
         const parameters = createDummyParameters(maxNonRestArgs, maxArgsParameterSymbolNames, /* types */ undefined, minArgumentCount, /*inJs*/ false);

src/services/codefixes/inferFromUsage.ts

@@ -1112,7 +1112,7 @@ namespace ts.codefix {
             }
             const returnType = combineFromUsage(combineUsages(calls.map(call => call.return_)));
             // TODO: GH#18217
-            return checker.createSignature(/*declaration*/ undefined!, /*typeParameters*/ undefined, /*thisParameter*/ undefined, parameters, returnType, /*typePredicate*/ undefined, length, /*hasRestParameter*/ false, /*hasLiteralTypes*/ false);
+            return checker.createSignature(/*declaration*/ undefined!, /*typeParameters*/ undefined, /*thisParameter*/ undefined, parameters, returnType, /*typePredicate*/ undefined, length, SignatureFlags.None);
         }
 
         function addCandidateType(usage: Usage, type: Type | undefined) {

src/services/services.ts

@@ -464,6 +464,7 @@ namespace ts {
     }
 
     class SignatureObject implements Signature {
+        flags: SignatureFlags;
         checker: TypeChecker;
         declaration!: SignatureDeclaration;
         typeParameters?: TypeParameter[];
@@ -473,8 +474,6 @@ namespace ts {
         resolvedTypePredicate: TypePredicate | undefined;
         minTypeArgumentCount!: number;
         minArgumentCount!: number;
-        hasRestParameter!: boolean;
-        hasLiteralTypes!: boolean;
 
         // Undefined is used to indicate the value has not been computed. If, after computing, the
         // symbol has no doc comment, then the empty array will be returned.
@@ -484,9 +483,11 @@ namespace ts {
         // symbol has no doc comment, then the empty array will be returned.
         jsDocTags?: JSDocTagInfo[];
 
-        constructor(checker: TypeChecker) {
+        constructor(checker: TypeChecker, flags: SignatureFlags) {
             this.checker = checker;
+            this.flags = flags;
         }
+
         getDeclaration(): SignatureDeclaration {
             return this.declaration;
         }

src/services/stringCompletions.ts

@@ -204,7 +204,7 @@ namespace ts.Completions.StringCompletions {
         const candidates: Signature[] = [];
         checker.getResolvedSignature(argumentInfo.invocation, candidates, argumentInfo.argumentCount);
         const types = flatMap(candidates, candidate => {
-            if (!candidate.hasRestParameter && argumentInfo.argumentCount > candidate.parameters.length) return;
+            if (!signatureHasRestParameter(candidate) && argumentInfo.argumentCount > candidate.parameters.length) return;
             const type = checker.getParameterType(candidate, argumentInfo.argumentIndex);
             isNewIdentifier = isNewIdentifier || !!(type.flags & TypeFlags.String);
             return getStringLiteralTypes(type, uniques);