Improve soundness of indexed access types

src/compiler/parser.ts

@@ -7784,7 +7784,7 @@ namespace ts {
                     const referencedFiles = context.referencedFiles;
                     const typeReferenceDirectives = context.typeReferenceDirectives;
                     const libReferenceDirectives = context.libReferenceDirectives;
-                    forEach(toArray(entryOrList), (arg: PragmaPseudoMap["reference"]) => {
+                    forEach(toArray(entryOrList) as PragmaPseudoMap["reference"][], arg => {
                         const { types, lib, path } = arg.arguments;
                         if (arg.arguments["no-default-lib"]) {
                             context.hasNoDefaultLib = true;
@@ -7806,8 +7806,8 @@ namespace ts {
                 }
                 case "amd-dependency": {
                     context.amdDependencies = map(
-                        toArray(entryOrList),
-                        (x: PragmaPseudoMap["amd-dependency"]) => ({ name: x.arguments.name, path: x.arguments.path }));
+                        toArray(entryOrList) as PragmaPseudoMap["amd-dependency"][],
+                        x => ({ name: x.arguments.name, path: x.arguments.path }));
                     break;
                 }
                 case "amd-module": {

src/compiler/types.ts

@@ -4279,7 +4279,8 @@ namespace ts {
         objectType: Type;
         indexType: Type;
         constraint?: Type;
-        simplified?: Type;
+        simplifiedForReading?: Type;
+        simplifiedForWriting?: Type;
     }
 
     export type TypeVariable = TypeParameter | IndexedAccessType;

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -2359,7 +2359,8 @@ declare namespace ts {
         objectType: Type;
         indexType: Type;
         constraint?: Type;
-        simplified?: Type;
+        simplifiedForReading?: Type;
+        simplifiedForWriting?: Type;
     }
     type TypeVariable = TypeParameter | IndexedAccessType;
     interface IndexType extends InstantiableType {

tests/baselines/reference/api/typescript.d.ts

@@ -2359,7 +2359,8 @@ declare namespace ts {
         objectType: Type;
         indexType: Type;
         constraint?: Type;
-        simplified?: Type;
+        simplifiedForReading?: Type;
+        simplifiedForWriting?: Type;
     }
     type TypeVariable = TypeParameter | IndexedAccessType;
     interface IndexType extends InstantiableType {

tests/baselines/reference/infiniteConstraints.errors.txt

@@ -1,4 +1,3 @@
-tests/cases/compiler/infiniteConstraints.ts(3,37): error TS2589: Type instantiation is excessively deep and possibly infinite.
 tests/cases/compiler/infiniteConstraints.ts(4,37): error TS2536: Type '"val"' cannot be used to index type 'B[Exclude<keyof B, K>]'.
 tests/cases/compiler/infiniteConstraints.ts(21,21): error TS2536: Type '"val"' cannot be used to index type 'Extract<T[K], Record<"val", string>>'.
 tests/cases/compiler/infiniteConstraints.ts(21,57): error TS2536: Type '"val"' cannot be used to index type 'Extract<T[Exclude<keyof T, K>], Record<"val", string>>'.
@@ -7,12 +6,10 @@ tests/cases/compiler/infiniteConstraints.ts(31,63): error TS2322: Type 'Record<"
 tests/cases/compiler/infiniteConstraints.ts(36,71): error TS2536: Type '"foo"' cannot be used to index type 'T[keyof T]'.
 
 
-==== tests/cases/compiler/infiniteConstraints.ts (7 errors) ====
+==== tests/cases/compiler/infiniteConstraints.ts (6 errors) ====
     // Both of the following types trigger the recursion limiter in getImmediateBaseConstraint
 
     type T1<B extends { [K in keyof B]: Extract<B[Exclude<keyof B, K>], { val: string }>["val"] }> = B;
-                                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
     type T2<B extends { [K in keyof B]: B[Exclude<keyof B, K>]["val"] }> = B;
                                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2536: Type '"val"' cannot be used to index type 'B[Exclude<keyof B, K>]'.

tests/baselines/reference/keyofAndIndexedAccess.types

@@ -1794,7 +1794,7 @@ function updateIds2<T extends { [x: string]: string }, K extends keyof T>(
 >key : K
 
     stringMap[x]; // Should be OK.
->stringMap[x] : { [oldId: string]: string; }[T[K]]
+>stringMap[x] : string
 >stringMap : { [oldId: string]: string; }
 >x : T[K]
 }

tests/baselines/reference/keyofAndIndexedAccess2.errors.txt

@@ -0,0 +1,190 @@
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(4,5): error TS2322: Type '"x"' is not assignable to type 'number'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(6,5): error TS2322: Type '2' is not assignable to type '0 | 1'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(7,5): error TS2322: Type '"x"' is not assignable to type '0 | 1'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(8,5): error TS2322: Type '1' is not assignable to type 'never'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(9,5): error TS2322: Type '2' is not assignable to type 'never'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(10,5): error TS2322: Type '"x"' is not assignable to type 'never'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(14,5): error TS2739: Type '{ [key: string]: number; }' is missing the following properties from type '{ x: number; y: number; }': x, y
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(15,5): error TS2322: Type 'T' is not assignable to type '{ x: number; y: number; }'.
+  Type '{ [key: string]: number; }' is missing the following properties from type '{ x: number; y: number; }': x, y
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(18,5): error TS2322: Type '{ x: number; y: number; }' is not assignable to type 'T'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(19,5): error TS2322: Type '{ [key: string]: number; }' is not assignable to type 'T'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(26,7): error TS2339: Property 'x' does not exist on type 'T'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(27,5): error TS2322: Type '1' is not assignable to type 'T[keyof T]'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(31,5): error TS2322: Type '{ [key: string]: number; }' is not assignable to type '{ [P in K]: number; }'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(38,5): error TS2322: Type '{ [x: string]: number; }' is not assignable to type '{ [P in K]: number; }'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(50,3): error TS7017: Element implicitly has an 'any' type because type 'Item' has no index signature.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(51,3): error TS2322: Type '123' is not assignable to type 'string & number'.
+  Type '123' is not assignable to type 'string'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(52,3): error TS2322: Type '123' is not assignable to type 'T[keyof T]'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(53,3): error TS2322: Type '123' is not assignable to type 'T[K]'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(65,7): error TS2339: Property 'foo' does not exist on type 'T'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(66,3): error TS2536: Type 'string' cannot be used to index type 'T'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(67,3): error TS2322: Type '123' is not assignable to type 'T[keyof T]'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(68,3): error TS2322: Type '123' is not assignable to type 'T[K]'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(108,5): error TS2322: Type '123' is not assignable to type 'Type[K]'.
+  Type '123' is not assignable to type '123 & "some string"'.
+    Type '123' is not assignable to type '"some string"'.
+
+
+==== tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts (23 errors) ====
+    function f1(obj: { a: number, b: 0 | 1, c: string }, k0: 'a', k1: 'a' | 'b', k2: 'a' | 'b' | 'c') {
+        obj[k0] = 1;
+        obj[k0] = 2;
+        obj[k0] = 'x';  // Error
+        ~~~~~~~
+!!! error TS2322: Type '"x"' is not assignable to type 'number'.
+        obj[k1] = 1;
+        obj[k1] = 2;    // Error
+        ~~~~~~~
+!!! error TS2322: Type '2' is not assignable to type '0 | 1'.
+        obj[k1] = 'x';  // Error
+        ~~~~~~~
+!!! error TS2322: Type '"x"' is not assignable to type '0 | 1'.
+        obj[k2] = 1;    // Error
+        ~~~~~~~
+!!! error TS2322: Type '1' is not assignable to type 'never'.
+        obj[k2] = 2;    // Error
+        ~~~~~~~
+!!! error TS2322: Type '2' is not assignable to type 'never'.
+        obj[k2] = 'x';  // Error
+        ~~~~~~~
+!!! error TS2322: Type '"x"' is not assignable to type 'never'.
+    }
+
+    function f2<T extends { [key: string]: number }>(a: { x: number, y: number }, b: { [key: string]: number }, c: T, k: keyof T) {
+        a = b;  // Error, index signature in source doesn't imply properties are present
+        ~
+!!! error TS2739: Type '{ [key: string]: number; }' is missing the following properties from type '{ x: number; y: number; }': x, y
+        a = c;  // Error, index signature in source doesn't imply properties are present
+        ~
+!!! error TS2322: Type 'T' is not assignable to type '{ x: number; y: number; }'.
+!!! error TS2322:   Type '{ [key: string]: number; }' is missing the following properties from type '{ x: number; y: number; }': x, y
+        b = a;
+        b = c;
+        c = a;  // Error, constraint on target doesn't imply any properties or signatures
+        ~
+!!! error TS2322: Type '{ x: number; y: number; }' is not assignable to type 'T'.
+        c = b;  // Error, constraint on target doesn't imply any properties or signatures
+        ~
+!!! error TS2322: Type '{ [key: string]: number; }' is not assignable to type 'T'.
+        a.x;
+        b.x;
+        c.x;
+        c[k];
+        a.x = 1;
+        b.x = 1;
+        c.x = 1;  // Error, cannot write to index signature through constraint
+          ~
+!!! error TS2339: Property 'x' does not exist on type 'T'.
+        c[k] = 1; // Error, cannot write to index signature through constraint
+        ~~~~
+!!! error TS2322: Type '1' is not assignable to type 'T[keyof T]'.
+    }
+
+    function f3<K extends string>(a: { [P in K]: number }, b: { [key: string]: number }, k: K) {
+        a = b;  // Error, index signature doesn't imply properties are present
+        ~
+!!! error TS2322: Type '{ [key: string]: number; }' is not assignable to type '{ [P in K]: number; }'.
+        b = a;
+        a[k];
+        a[k] = 1;
+    }
+
+    function f3b<K extends string>(a: { [P in K]: number }, b: { [P in string]: number }, k: K) {
+        a = b;  // Error, index signature doesn't imply properties are present
+        ~
+!!! error TS2322: Type '{ [x: string]: number; }' is not assignable to type '{ [P in K]: number; }'.
+        b = a;
+    }
+
+    function f4<K extends string>(a: { [key: string]: number }[K], b: number) {
+      a = b;
+      b = a;
+    }
+
+    type Item = { a: string, b: number };
+
+    function f10<T extends Item, K extends keyof T>(obj: T, k1: string, k2: keyof Item, k3: keyof T, k4: K) {
+      obj[k1] = 123;  // Error
+      ~~~~~~~
+!!! error TS7017: Element implicitly has an 'any' type because type 'Item' has no index signature.
+      obj[k2] = 123;  // Error
+      ~~~~~~~
+!!! error TS2322: Type '123' is not assignable to type 'string & number'.
+!!! error TS2322:   Type '123' is not assignable to type 'string'.
+      obj[k3] = 123;  // Error
+      ~~~~~~~
+!!! error TS2322: Type '123' is not assignable to type 'T[keyof T]'.
+      obj[k4] = 123;  // Error
+      ~~~~~~~
+!!! error TS2322: Type '123' is not assignable to type 'T[K]'.
+    }
+
+    type Dict = Record<string, number>;
+
+    function f11<K extends keyof Dict>(obj: Dict, k1: keyof Dict, k2: K) {
+      obj.foo = 123;
+      obj[k1] = 123;
+      obj[k2] = 123;
+    }
+
+    function f12<T extends Readonly<Dict>, K extends keyof T>(obj: T, k1: keyof Dict, k2: keyof T, k3: K) {
+      obj.foo = 123;  // Error
+          ~~~
+!!! error TS2339: Property 'foo' does not exist on type 'T'.
+      obj[k1] = 123;  // Error
+      ~~~~~~~
+!!! error TS2536: Type 'string' cannot be used to index type 'T'.
+      obj[k2] = 123;  // Error
+      ~~~~~~~
+!!! error TS2322: Type '123' is not assignable to type 'T[keyof T]'.
+      obj[k3] = 123;  // Error
+      ~~~~~~~
+!!! error TS2322: Type '123' is not assignable to type 'T[K]'.
+    }
+
+    // Repro from #27895
+
+    export interface Entity {
+        id: number | string;
+    }
+
+    export type IdOf<E extends Entity> = E['id'];
+
+    export interface EntityState<E extends Entity> {
+        ids: IdOf<E>[];
+        entities: { [key: string]: E, [key: number]: E };
+    }
+
+
+    export function getAllEntities<E extends Entity>(state: EntityState<E>): E[] {
+        const { ids, entities } = state;
+        return ids.map(id => entities[id]);
+    }
+
+    export function getEntity<E extends Entity>(id: IdOf<E>, state: EntityState<E>): E | undefined {
+        const { ids, entities } = state;
+
+        if (!ids.includes(id)) {
+            return undefined;
+        }
+
+        return entities[id];
+    }
+
+    // Repro from #30603
+
+    interface Type {
+        a: 123;
+        b: "some string";
+    }
+
+    function get123<K extends keyof Type>(): Type[K] {
+        return 123;  // Error
+        ~~~~~~~~~~~
+!!! error TS2322: Type '123' is not assignable to type 'Type[K]'.
+!!! error TS2322:   Type '123' is not assignable to type '123 & "some string"'.
+!!! error TS2322:     Type '123' is not assignable to type '"some string"'.
+    }
+