Fix crash when serializing the return type of a generic call to Array.prototype.flat

src/compiler/checker.ts

@@ -4404,8 +4404,8 @@ namespace ts {
                     context.inferTypeParameters = (<ConditionalType>type).root.inferTypeParameters;
                     const extendsTypeNode = typeToTypeNodeHelper((<ConditionalType>type).extendsType, context);
                     context.inferTypeParameters = saveInferTypeParameters;
-                    const trueTypeNode = typeToTypeNodeHelper(getTrueTypeFromConditionalType(<ConditionalType>type), context);
-                    const falseTypeNode = typeToTypeNodeHelper(getFalseTypeFromConditionalType(<ConditionalType>type), context);
+                    const trueTypeNode = typeToTypeNodeOrCircularityEllision(getTrueTypeFromConditionalType(<ConditionalType>type));
+                    const falseTypeNode = typeToTypeNodeOrCircularityEllision(getFalseTypeFromConditionalType(<ConditionalType>type));
                     context.approximateLength += 15;
                     return createConditionalTypeNode(checkTypeNode, extendsTypeNode, trueTypeNode, falseTypeNode);
                 }
@@ -4415,6 +4415,21 @@ namespace ts {
 
                 return Debug.fail("Should be unreachable.");
 
+
+                function typeToTypeNodeOrCircularityEllision(type: Type) {
+                    if (type.flags & TypeFlags.Union) {
+                        if (context.visitedTypes && context.visitedTypes.has("" + getTypeId(type))) {
+                            if (!(context.flags & NodeBuilderFlags.AllowAnonymousIdentifier)) {
+                                context.encounteredError = true;
+                                context.tracker?.reportCyclicStructureError?.();
+                            }
+                            return createElidedInformationPlaceholder(context);
+                        }
+                        return visitAndTransformType(type, type => typeToTypeNodeHelper(type, context));
+                    }
+                    return typeToTypeNodeHelper(type, context);
+                }
+
                 function createMappedTypeNodeFromType(type: MappedType) {
                     Debug.assert(!!(type.flags & TypeFlags.Object));
                     const readonlyToken = type.declaration.readonlyToken ? <ReadonlyToken | PlusToken | MinusToken>createToken(type.declaration.readonlyToken.kind) : undefined;
@@ -12913,10 +12928,12 @@ namespace ts {
             return links.resolvedType;
         }
 
-        function createIndexedAccessType(objectType: Type, indexType: Type) {
+        function createIndexedAccessType(objectType: Type, indexType: Type, aliasSymbol: Symbol | undefined, aliasTypeArguments: readonly Type[] | undefined) {
             const type = <IndexedAccessType>createType(TypeFlags.IndexedAccess);
             type.objectType = objectType;
             type.indexType = indexType;
+            type.aliasSymbol = aliasSymbol;
+            type.aliasTypeArguments = aliasTypeArguments;
             return type;
         }
 
@@ -13251,11 +13268,11 @@ namespace ts {
             return instantiateType(getTemplateTypeFromMappedType(objectType), templateMapper);
         }
 
-        function getIndexedAccessType(objectType: Type, indexType: Type, accessNode?: ElementAccessExpression | IndexedAccessTypeNode | PropertyName | BindingName | SyntheticExpression): Type {
-            return getIndexedAccessTypeOrUndefined(objectType, indexType, accessNode, AccessFlags.None) || (accessNode ? errorType : unknownType);
+        function getIndexedAccessType(objectType: Type, indexType: Type, accessNode?: ElementAccessExpression | IndexedAccessTypeNode | PropertyName | BindingName | SyntheticExpression, aliasSymbol?: Symbol, aliasTypeArguments?: readonly Type[]): Type {
+            return getIndexedAccessTypeOrUndefined(objectType, indexType, accessNode, AccessFlags.None, aliasSymbol, aliasTypeArguments) || (accessNode ? errorType : unknownType);
         }
 
-        function getIndexedAccessTypeOrUndefined(objectType: Type, indexType: Type, accessNode?: ElementAccessExpression | IndexedAccessTypeNode | PropertyName | BindingName | SyntheticExpression, accessFlags = AccessFlags.None): Type | undefined {
+        function getIndexedAccessTypeOrUndefined(objectType: Type, indexType: Type, accessNode?: ElementAccessExpression | IndexedAccessTypeNode | PropertyName | BindingName | SyntheticExpression, accessFlags = AccessFlags.None, aliasSymbol?: Symbol, aliasTypeArguments?: readonly Type[]): Type | undefined {
             if (objectType === wildcardType || indexType === wildcardType) {
                 return wildcardType;
             }
@@ -13277,7 +13294,7 @@ namespace ts {
                 const id = objectType.id + "," + indexType.id;
                 let type = indexedAccessTypes.get(id);
                 if (!type) {
-                    indexedAccessTypes.set(id, type = createIndexedAccessType(objectType, indexType));
+                    indexedAccessTypes.set(id, type = createIndexedAccessType(objectType, indexType, aliasSymbol, aliasTypeArguments));
                 }
                 return type;
             }
@@ -13305,7 +13322,7 @@ namespace ts {
                 if (wasMissingProp) {
                     return undefined;
                 }
-                return accessFlags & AccessFlags.Writing ? getIntersectionType(propTypes) : getUnionType(propTypes);
+                return accessFlags & AccessFlags.Writing ? getIntersectionType(propTypes, aliasSymbol, aliasTypeArguments) : getUnionType(propTypes, UnionReduction.Literal, aliasSymbol, aliasTypeArguments);
             }
             return getPropertyTypeForIndexType(objectType, apparentObjectType, indexType, indexType, /* supressNoImplicitAnyError */ false, accessNode, accessFlags | AccessFlags.CacheSymbol);
         }
@@ -13315,7 +13332,8 @@ namespace ts {
             if (!links.resolvedType) {
                 const objectType = getTypeFromTypeNode(node.objectType);
                 const indexType = getTypeFromTypeNode(node.indexType);
-                const resolved = getIndexedAccessType(objectType, indexType, node);
+                const potentialAlias = getAliasSymbolForTypeNode(node);
+                const resolved = getIndexedAccessType(objectType, indexType, node, potentialAlias, getTypeArgumentsForAliasSymbol(potentialAlias));
                 links.resolvedType = resolved.flags & TypeFlags.IndexedAccess &&
                     (<IndexedAccessType>resolved).objectType === objectType &&
                     (<IndexedAccessType>resolved).indexType === indexType ?
@@ -14466,7 +14484,7 @@ namespace ts {
                 return getIndexType(instantiateType((<IndexType>type).type, mapper));
             }
             if (flags & TypeFlags.IndexedAccess) {
-                return getIndexedAccessType(instantiateType((<IndexedAccessType>type).objectType, mapper), instantiateType((<IndexedAccessType>type).indexType, mapper));
+                return getIndexedAccessType(instantiateType((<IndexedAccessType>type).objectType, mapper), instantiateType((<IndexedAccessType>type).indexType, mapper), /*accessNode*/ undefined, type.aliasSymbol, instantiateTypes(type.aliasTypeArguments, mapper));
             }
             if (flags & TypeFlags.Conditional) {
                 return getConditionalTypeInstantiation(<ConditionalType>type, combineTypeMappers((<ConditionalType>type).mapper, mapper));

src/compiler/diagnosticMessages.json

@@ -3533,6 +3533,10 @@
         "category": "Error",
         "code": 5087
     },
+    "The inferred type of '{0}' references a type with a cyclic structure which cannot be trivially serialized. A type annotation is necessary.": {
+        "category": "Error",
+        "code": 5088
+    },
 
     "Generates a sourcemap for each corresponding '.d.ts' file.": {
         "category": "Message",

src/compiler/transformers/declarations.ts

@@ -72,6 +72,7 @@ namespace ts {
             trackSymbol,
             reportInaccessibleThisError,
             reportInaccessibleUniqueSymbolError,
+            reportCyclicStructureError,
             reportPrivateInBaseOfClassExpression,
             reportLikelyUnsafeImportRequiredError,
             moduleResolverHost: host,
@@ -175,6 +176,13 @@ namespace ts {
             }
         }
 
+        function reportCyclicStructureError() {
+            if (errorNameNode) {
+                context.addDiagnostic(createDiagnosticForNode(errorNameNode, Diagnostics.The_inferred_type_of_0_references_a_type_with_a_cyclic_structure_which_cannot_be_trivially_serialized_A_type_annotation_is_necessary,
+                    declarationNameToString(errorNameNode)));
+            }
+        }
+
         function reportInaccessibleThisError() {
             if (errorNameNode) {
                 context.addDiagnostic(createDiagnosticForNode(errorNameNode, Diagnostics.The_inferred_type_of_0_references_an_inaccessible_1_type_A_type_annotation_is_necessary,

src/compiler/types.ts

@@ -6481,6 +6481,7 @@ namespace ts {
         reportInaccessibleThisError?(): void;
         reportPrivateInBaseOfClassExpression?(propertyName: string): void;
         reportInaccessibleUniqueSymbolError?(): void;
+        reportCyclicStructureError?(): void;
         reportLikelyUnsafeImportRequiredError?(specifier: string): void;
         moduleResolverHost?: ModuleSpecifierResolutionHost & { getCommonSourceDirectory(): string };
         trackReferencedAmbientModule?(decl: ModuleDeclaration, symbol: Symbol): void;

tests/baselines/reference/arrayFlatNoCrashInference.js

@@ -0,0 +1,10 @@
+//// [arrayFlatNoCrashInference.ts]
+function foo<T>(arr: T[], depth: number) {
+    return arr.flat(depth);
+}
+
+//// [arrayFlatNoCrashInference.js]
+"use strict";
+function foo(arr, depth) {
+    return arr.flat(depth);
+}

tests/baselines/reference/arrayFlatNoCrashInference.symbols

@@ -0,0 +1,14 @@
+=== tests/cases/compiler/arrayFlatNoCrashInference.ts ===
+function foo<T>(arr: T[], depth: number) {
+>foo : Symbol(foo, Decl(arrayFlatNoCrashInference.ts, 0, 0))
+>T : Symbol(T, Decl(arrayFlatNoCrashInference.ts, 0, 13))
+>arr : Symbol(arr, Decl(arrayFlatNoCrashInference.ts, 0, 16))
+>T : Symbol(T, Decl(arrayFlatNoCrashInference.ts, 0, 13))
+>depth : Symbol(depth, Decl(arrayFlatNoCrashInference.ts, 0, 25))
+
+    return arr.flat(depth);
+>arr.flat : Symbol(Array.flat, Decl(lib.es2019.array.d.ts, --, --))
+>arr : Symbol(arr, Decl(arrayFlatNoCrashInference.ts, 0, 16))
+>flat : Symbol(Array.flat, Decl(lib.es2019.array.d.ts, --, --))
+>depth : Symbol(depth, Decl(arrayFlatNoCrashInference.ts, 0, 25))
+}

tests/baselines/reference/arrayFlatNoCrashInference.types

@@ -0,0 +1,13 @@
+=== tests/cases/compiler/arrayFlatNoCrashInference.ts ===
+function foo<T>(arr: T[], depth: number) {
+>foo : <T>(arr: T[], depth: number) => FlatArray<T, 0 | 1 | -1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20>[]
+>arr : T[]
+>depth : number
+
+    return arr.flat(depth);
+>arr.flat(depth) : FlatArray<T, 0 | 1 | -1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20>[]
+>arr.flat : <A, D extends number = 1>(this: A, depth?: D | undefined) => FlatArray<A, D>[]
+>arr : T[]
+>flat : <A, D extends number = 1>(this: A, depth?: D | undefined) => FlatArray<A, D>[]
+>depth : number
+}

tests/baselines/reference/arrayFlatNoCrashInferenceDeclarations.js

@@ -0,0 +1,14 @@
+//// [arrayFlatNoCrashInferenceDeclarations.ts]
+function foo<T>(arr: T[], depth: number) {
+    return arr.flat(depth);
+}
+
+//// [arrayFlatNoCrashInferenceDeclarations.js]
+"use strict";
+function foo(arr, depth) {
+    return arr.flat(depth);
+}
+
+
+//// [arrayFlatNoCrashInferenceDeclarations.d.ts]
+declare function foo<T>(arr: T[], depth: number): FlatArray<T, 0 | 1 | -1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20>[];

tests/baselines/reference/arrayFlatNoCrashInferenceDeclarations.symbols

@@ -0,0 +1,14 @@
+=== tests/cases/compiler/arrayFlatNoCrashInferenceDeclarations.ts ===
+function foo<T>(arr: T[], depth: number) {
+>foo : Symbol(foo, Decl(arrayFlatNoCrashInferenceDeclarations.ts, 0, 0))
+>T : Symbol(T, Decl(arrayFlatNoCrashInferenceDeclarations.ts, 0, 13))
+>arr : Symbol(arr, Decl(arrayFlatNoCrashInferenceDeclarations.ts, 0, 16))
+>T : Symbol(T, Decl(arrayFlatNoCrashInferenceDeclarations.ts, 0, 13))
+>depth : Symbol(depth, Decl(arrayFlatNoCrashInferenceDeclarations.ts, 0, 25))
+
+    return arr.flat(depth);
+>arr.flat : Symbol(Array.flat, Decl(lib.es2019.array.d.ts, --, --))
+>arr : Symbol(arr, Decl(arrayFlatNoCrashInferenceDeclarations.ts, 0, 16))
+>flat : Symbol(Array.flat, Decl(lib.es2019.array.d.ts, --, --))
+>depth : Symbol(depth, Decl(arrayFlatNoCrashInferenceDeclarations.ts, 0, 25))
+}

tests/baselines/reference/arrayFlatNoCrashInferenceDeclarations.types

@@ -0,0 +1,13 @@
+=== tests/cases/compiler/arrayFlatNoCrashInferenceDeclarations.ts ===
+function foo<T>(arr: T[], depth: number) {
+>foo : <T>(arr: T[], depth: number) => FlatArray<T, 0 | 1 | -1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20>[]
+>arr : T[]
+>depth : number
+
+    return arr.flat(depth);
+>arr.flat(depth) : FlatArray<T, 0 | 1 | -1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20>[]
+>arr.flat : <A, D extends number = 1>(this: A, depth?: D | undefined) => FlatArray<A, D>[]
+>arr : T[]
+>flat : <A, D extends number = 1>(this: A, depth?: D | undefined) => FlatArray<A, D>[]
+>depth : number
+}

tests/baselines/reference/bigintWithLib.errors.txt

@@ -9,17 +9,17 @@ tests/cases/compiler/bigintWithLib.ts(16,33): error TS2769: No overload matches
           Type 'IteratorYieldResult<number>' is not assignable to type 'IteratorResult<bigint, any>'.
             Type 'IteratorYieldResult<number>' is not assignable to type 'IteratorYieldResult<bigint>'.
               Type 'number' is not assignable to type 'bigint'.
-  Overload 3 of 3, '(buffer: ArrayBuffer | SharedArrayBuffer, byteOffset?: number, length?: number): BigInt64Array', gave the following error.
-    Argument of type 'number[]' is not assignable to parameter of type 'ArrayBuffer | SharedArrayBuffer'.
+  Overload 3 of 3, '(buffer: ArrayBufferLike, byteOffset?: number, length?: number): BigInt64Array', gave the following error.
+    Argument of type 'number[]' is not assignable to parameter of type 'ArrayBufferLike'.
       Type 'number[]' is missing the following properties from type 'SharedArrayBuffer': byteLength, [Symbol.species], [Symbol.toStringTag]
 tests/cases/compiler/bigintWithLib.ts(21,13): error TS2540: Cannot assign to 'length' because it is a read-only property.
 tests/cases/compiler/bigintWithLib.ts(28,35): error TS2769: No overload matches this call.
   Overload 1 of 3, '(length?: number): BigUint64Array', gave the following error.
     Argument of type 'number[]' is not assignable to parameter of type 'number'.
   Overload 2 of 3, '(array: Iterable<bigint>): BigUint64Array', gave the following error.
     Argument of type 'number[]' is not assignable to parameter of type 'Iterable<bigint>'.
-  Overload 3 of 3, '(buffer: ArrayBuffer | SharedArrayBuffer, byteOffset?: number, length?: number): BigUint64Array', gave the following error.
-    Argument of type 'number[]' is not assignable to parameter of type 'ArrayBuffer | SharedArrayBuffer'.
+  Overload 3 of 3, '(buffer: ArrayBufferLike, byteOffset?: number, length?: number): BigUint64Array', gave the following error.
+    Argument of type 'number[]' is not assignable to parameter of type 'ArrayBufferLike'.
       Type 'number[]' is not assignable to type 'SharedArrayBuffer'.
 tests/cases/compiler/bigintWithLib.ts(33,13): error TS2540: Cannot assign to 'length' because it is a read-only property.
 tests/cases/compiler/bigintWithLib.ts(40,25): error TS2345: Argument of type 'number' is not assignable to parameter of type 'bigint'.
@@ -56,8 +56,8 @@ tests/cases/compiler/bigintWithLib.ts(43,26): error TS2345: Argument of type 'nu
 !!! error TS2769:           Type 'IteratorYieldResult<number>' is not assignable to type 'IteratorResult<bigint, any>'.
 !!! error TS2769:             Type 'IteratorYieldResult<number>' is not assignable to type 'IteratorYieldResult<bigint>'.
 !!! error TS2769:               Type 'number' is not assignable to type 'bigint'.
-!!! error TS2769:   Overload 3 of 3, '(buffer: ArrayBuffer | SharedArrayBuffer, byteOffset?: number, length?: number): BigInt64Array', gave the following error.
-!!! error TS2769:     Argument of type 'number[]' is not assignable to parameter of type 'ArrayBuffer | SharedArrayBuffer'.
+!!! error TS2769:   Overload 3 of 3, '(buffer: ArrayBufferLike, byteOffset?: number, length?: number): BigInt64Array', gave the following error.
+!!! error TS2769:     Argument of type 'number[]' is not assignable to parameter of type 'ArrayBufferLike'.
 !!! error TS2769:       Type 'number[]' is missing the following properties from type 'SharedArrayBuffer': byteLength, [Symbol.species], [Symbol.toStringTag]
     bigIntArray = new BigInt64Array(new ArrayBuffer(80));
     bigIntArray = new BigInt64Array(new ArrayBuffer(80), 8);
@@ -79,8 +79,8 @@ tests/cases/compiler/bigintWithLib.ts(43,26): error TS2345: Argument of type 'nu
 !!! error TS2769:     Argument of type 'number[]' is not assignable to parameter of type 'number'.
 !!! error TS2769:   Overload 2 of 3, '(array: Iterable<bigint>): BigUint64Array', gave the following error.
 !!! error TS2769:     Argument of type 'number[]' is not assignable to parameter of type 'Iterable<bigint>'.
-!!! error TS2769:   Overload 3 of 3, '(buffer: ArrayBuffer | SharedArrayBuffer, byteOffset?: number, length?: number): BigUint64Array', gave the following error.
-!!! error TS2769:     Argument of type 'number[]' is not assignable to parameter of type 'ArrayBuffer | SharedArrayBuffer'.
+!!! error TS2769:   Overload 3 of 3, '(buffer: ArrayBufferLike, byteOffset?: number, length?: number): BigUint64Array', gave the following error.
+!!! error TS2769:     Argument of type 'number[]' is not assignable to parameter of type 'ArrayBufferLike'.
 !!! error TS2769:       Type 'number[]' is not assignable to type 'SharedArrayBuffer'.
     bigUintArray = new BigUint64Array(new ArrayBuffer(80));
     bigUintArray = new BigUint64Array(new ArrayBuffer(80), 8);