Better compatibility error for indexed access type (microsoft#51228)

Author: matiasosorio1999

src/compiler/checker.ts

@@ -20204,26 +20204,31 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 generalizedSourceType = getTypeNameForErrorDisplay(generalizedSource);
             }
 
-            if (target.flags & TypeFlags.TypeParameter && target !== markerSuperTypeForCheck && target !== markerSubTypeForCheck) {
-                const constraint = getBaseConstraintOfType(target);
-                let needsOriginalSource;
-                if (constraint && (isTypeAssignableTo(generalizedSource, constraint) || (needsOriginalSource = isTypeAssignableTo(source, constraint)))) {
-                    reportError(
-                        Diagnostics._0_is_assignable_to_the_constraint_of_type_1_but_1_could_be_instantiated_with_a_different_subtype_of_constraint_2,
-                        needsOriginalSource ? sourceType : generalizedSourceType,
-                        targetType,
-                        typeToString(constraint),
-                    );
-                }
-                else {
-                    errorInfo = undefined;
-                    reportError(
-                        Diagnostics._0_could_be_instantiated_with_an_arbitrary_type_which_could_be_unrelated_to_1,
-                        targetType,
-                        generalizedSourceType
-                    );
+                // If `target` is of indexed access type (And `source` it is not), we use the object type of `target` for better error reporting
+                const targetFlags = target.flags & TypeFlags.IndexedAccess && !(source.flags & TypeFlags.IndexedAccess) ?
+                    (target as IndexedAccessType).objectType.flags :
+                    target.flags;
+
+                if (targetFlags & TypeFlags.TypeParameter && target !== markerSuperTypeForCheck && target !== markerSubTypeForCheck) {
+                    const constraint = getBaseConstraintOfType(target);
+                    let needsOriginalSource;
+                    if (constraint && (isTypeAssignableTo(generalizedSource, constraint) || (needsOriginalSource = isTypeAssignableTo(source, constraint)))) {
+                        reportError(
+                            Diagnostics._0_is_assignable_to_the_constraint_of_type_1_but_1_could_be_instantiated_with_a_different_subtype_of_constraint_2,
+                            needsOriginalSource ? sourceType : generalizedSourceType,
+                            targetType,
+                            typeToString(constraint),
+                        );
+                    }
+                    else {
+                        errorInfo = undefined;
+                        reportError(
+                            Diagnostics._0_could_be_instantiated_with_an_arbitrary_type_which_could_be_unrelated_to_1,
+                            targetType,
+                            generalizedSourceType
+                        );
+                    }
                 }
-            }
 
             if (!message) {
                 if (relation === comparableRelation) {

tests/baselines/reference/conditionalTypes1.errors.txt

@@ -11,6 +11,7 @@ tests/cases/conformance/types/conditional/conditionalTypes1.ts(17,5): error TS23
 tests/cases/conformance/types/conditional/conditionalTypes1.ts(24,5): error TS2322: Type 'T[keyof T] | undefined' is not assignable to type 'NonNullable<Partial<T>[keyof T]>'.
   Type 'undefined' is not assignable to type 'T[keyof T] & {}'.
     Type 'undefined' is not assignable to type 'T[keyof T]'.
+      'T[keyof T]' could be instantiated with an arbitrary type which could be unrelated to 'undefined'.
 tests/cases/conformance/types/conditional/conditionalTypes1.ts(29,5): error TS2322: Type 'T["x"]' is not assignable to type 'NonNullable<T["x"]>'.
   Type 'string | undefined' is not assignable to type 'NonNullable<T["x"]>'.
     Type 'undefined' is not assignable to type 'NonNullable<T["x"]>'.
@@ -110,6 +111,7 @@ tests/cases/conformance/types/conditional/conditionalTypes1.ts(288,43): error TS
 !!! error TS2322: Type 'T[keyof T] | undefined' is not assignable to type 'NonNullable<Partial<T>[keyof T]>'.
 !!! error TS2322:   Type 'undefined' is not assignable to type 'T[keyof T] & {}'.
 !!! error TS2322:     Type 'undefined' is not assignable to type 'T[keyof T]'.
+!!! error TS2322:       'T[keyof T]' could be instantiated with an arbitrary type which could be unrelated to 'undefined'.
     }
 
     function f4<T extends { x: string | undefined }>(x: T["x"], y: NonNullable<T["x"]>) {

tests/baselines/reference/indexedAccessRelation.errors.txt

@@ -3,8 +3,7 @@ tests/cases/compiler/indexedAccessRelation.ts(16,23): error TS2345: Argument of
     Type 'T' is not assignable to type 'S["a"] & T'.
       Type 'Foo' is not assignable to type 'S["a"] & T'.
         Type 'Foo' is not assignable to type 'S["a"]'.
-          Type 'T' is not assignable to type 'S["a"]'.
-            Type 'Foo' is not assignable to type 'S["a"]'.
+          'S["a"]' could be instantiated with an arbitrary type which could be unrelated to 'Foo'.
 
 
 ==== tests/cases/compiler/indexedAccessRelation.ts (1 errors) ====
@@ -30,8 +29,7 @@ tests/cases/compiler/indexedAccessRelation.ts(16,23): error TS2345: Argument of
 !!! error TS2345:     Type 'T' is not assignable to type 'S["a"] & T'.
 !!! error TS2345:       Type 'Foo' is not assignable to type 'S["a"] & T'.
 !!! error TS2345:         Type 'Foo' is not assignable to type 'S["a"]'.
-!!! error TS2345:           Type 'T' is not assignable to type 'S["a"]'.
-!!! error TS2345:             Type 'Foo' is not assignable to type 'S["a"]'.
+!!! error TS2345:           'S["a"]' could be instantiated with an arbitrary type which could be unrelated to 'Foo'.
         }
     }
 

tests/baselines/reference/keyofAndIndexedAccess2.errors.txt

@@ -13,17 +13,22 @@ tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(19,5): error TS232
   '{ [key: string]: number; }' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{ [key: string]: number; }'.
 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 'number' is not assignable to type 'T[keyof T]'.
+  'number' is assignable to the constraint of type 'T[keyof T]', but 'T[keyof T]' could be instantiated with a different subtype of constraint 'number'.
 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 TS7053: Element implicitly has an 'any' type because expression of type 'string' can't be used to index type 'Item'.
   No index signature with a parameter of type 'string' was found on type 'Item'.
 tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(51,3): error TS2322: Type 'number' is not assignable to type 'never'.
 tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(52,3): error TS2322: Type 'number' is not assignable to type 'T[keyof T]'.
+  'T[keyof T]' could be instantiated with an arbitrary type which could be unrelated to 'number'.
 tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(53,3): error TS2322: Type 'number' is not assignable to type 'T[K]'.
+  'T[K]' could be instantiated with an arbitrary type which could be unrelated to 'number'.
 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 'number' is not assignable to type 'T[keyof T]'.
+  'number' is assignable to the constraint of type 'T[keyof T]', but 'T[keyof T]' could be instantiated with a different subtype of constraint 'number'.
 tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(68,3): error TS2322: Type 'number' is not assignable to type 'T[K]'.
+  'number' is assignable to the constraint of type 'T[K]', but 'T[K]' could be instantiated with a different subtype of constraint 'number'.
 tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(108,5): error TS2322: Type '123' is not assignable to type 'Type[K]'.
   Type 'number' is not assignable to type 'never'.
 
@@ -83,6 +88,7 @@ tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(108,5): error TS23
         c[k] = 1; // Error, cannot write to index signature through constraint
         ~~~~
 !!! error TS2322: Type 'number' is not assignable to type 'T[keyof T]'.
+!!! error TS2322:   'number' is assignable to the constraint of type 'T[keyof T]', but 'T[keyof T]' could be instantiated with a different subtype of constraint 'number'.
     }
 
     function f3<K extends string>(a: { [P in K]: number }, b: { [key: string]: number }, k: K) {
@@ -119,9 +125,11 @@ tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(108,5): error TS23
       obj[k3] = 123;  // Error
       ~~~~~~~
 !!! error TS2322: Type 'number' is not assignable to type 'T[keyof T]'.
+!!! error TS2322:   'T[keyof T]' could be instantiated with an arbitrary type which could be unrelated to 'number'.
       obj[k4] = 123;  // Error
       ~~~~~~~
 !!! error TS2322: Type 'number' is not assignable to type 'T[K]'.
+!!! error TS2322:   'T[K]' could be instantiated with an arbitrary type which could be unrelated to 'number'.
     }
 
     type Dict = Record<string, number>;
@@ -142,9 +150,11 @@ tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(108,5): error TS23
       obj[k2] = 123;  // Error
       ~~~~~~~
 !!! error TS2322: Type 'number' is not assignable to type 'T[keyof T]'.
+!!! error TS2322:   'number' is assignable to the constraint of type 'T[keyof T]', but 'T[keyof T]' could be instantiated with a different subtype of constraint 'number'.
       obj[k3] = 123;  // Error
       ~~~~~~~
 !!! error TS2322: Type 'number' is not assignable to type 'T[K]'.
+!!! error TS2322:   'number' is assignable to the constraint of type 'T[K]', but 'T[K]' could be instantiated with a different subtype of constraint 'number'.
     }
 
     // Repro from #27895

tests/baselines/reference/keyofAndIndexedAccessErrors.errors.txt

@@ -62,11 +62,16 @@ tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(117,5): error
 tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(122,5): error TS2322: Type 'number' is not assignable to type 'keyof T'.
 tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(123,5): error TS2322: Type 'string' is not assignable to type 'keyof T'.
 tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(140,5): error TS2322: Type 'number' is not assignable to type 'T[K]'.
+  'number' is assignable to the constraint of type 'T[K]', but 'T[K]' could be instantiated with a different subtype of constraint 'any'.
 tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(141,5): error TS2322: Type 'string' is not assignable to type 'T[K]'.
+  'string' is assignable to the constraint of type 'T[K]', but 'T[K]' could be instantiated with a different subtype of constraint 'any'.
 tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(142,5): error TS2322: Type 'number[]' is not assignable to type 'T[K]'.
+  'number[]' is assignable to the constraint of type 'T[K]', but 'T[K]' could be instantiated with a different subtype of constraint 'any'.
+tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(165,5): error TS2322: Type 'number' is not assignable to type 'T[keyof T]'.
+  'number' is assignable to the constraint of type 'T[keyof T]', but 'T[keyof T]' could be instantiated with a different subtype of constraint 'number'.
 
 
-==== tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts (40 errors) ====
+==== tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts (41 errors) ====
     class Shape {
         name: string;
         width: number;
@@ -312,12 +317,15 @@ tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(142,5): error
         t[k] = 42;  // Error
         ~~~~
 !!! error TS2322: Type 'number' is not assignable to type 'T[K]'.
+!!! error TS2322:   'number' is assignable to the constraint of type 'T[K]', but 'T[K]' could be instantiated with a different subtype of constraint 'any'.
         t[k] = "hello";  // Error
         ~~~~
 !!! error TS2322: Type 'string' is not assignable to type 'T[K]'.
+!!! error TS2322:   'string' is assignable to the constraint of type 'T[K]', but 'T[K]' could be instantiated with a different subtype of constraint 'any'.
         t[k] = [10, 20];  // Error
         ~~~~
 !!! error TS2322: Type 'number[]' is not assignable to type 'T[K]'.
+!!! error TS2322:   'number[]' is assignable to the constraint of type 'T[K]', but 'T[K]' could be instantiated with a different subtype of constraint 'any'.
     }
 
     // Repro from #28839
@@ -329,4 +337,23 @@ tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts(142,5): error
     function f31<T, K extends keyof T>() {
         let x: Partial<Partial<Partial<Partial<Partial<Partial<Partial<Record<keyof T, string>>>>>>>>[K] = "hello";
     }
+    
+    // Repro from #51069
+    
+    class Test<T extends Record<string, number>> {
+      testy: T;
+    
+      constructor(t: T) {
+        this.testy = t;
+      }
+    
+      public t(key: keyof T): number {
+        this.testy[key] += 1; // Error
+        ~~~~~~~~~~~~~~~
+!!! error TS2322: Type 'number' is not assignable to type 'T[keyof T]'.
+!!! error TS2322:   'number' is assignable to the constraint of type 'T[keyof T]', but 'T[keyof T]' could be instantiated with a different subtype of constraint 'number'.
+    
+        return this.testy[key];
+      }
+    }
 

tests/baselines/reference/keyofAndIndexedAccessErrors.js

@@ -152,6 +152,22 @@ function f30<T, K extends keyof T>() {
 function f31<T, K extends keyof T>() {
     let x: Partial<Partial<Partial<Partial<Partial<Partial<Partial<Record<keyof T, string>>>>>>>>[K] = "hello";
 }
+
+// Repro from #51069
+
+class Test<T extends Record<string, number>> {
+  testy: T;
+
+  constructor(t: T) {
+    this.testy = t;
+  }
+
+  public t(key: keyof T): number {
+    this.testy[key] += 1; // Error
+
+    return this.testy[key];
+  }
+}
 
 
 //// [keyofAndIndexedAccessErrors.js]
@@ -232,3 +248,14 @@ function f30() {
 function f31() {
     var x = "hello";
 }
+// Repro from #51069
+var Test = /** @class */ (function () {
+    function Test(t) {
+        this.testy = t;
+    }
+    Test.prototype.t = function (key) {
+        this.testy[key] += 1; // Error
+        return this.testy[key];
+    };
+    return Test;
+}());

tests/baselines/reference/keyofAndIndexedAccessErrors.symbols

@@ -523,3 +523,44 @@ function f31<T, K extends keyof T>() {
 >K : Symbol(K, Decl(keyofAndIndexedAccessErrors.ts, 150, 15))
 }
 
+// Repro from #51069
+
+class Test<T extends Record<string, number>> {
+>Test : Symbol(Test, Decl(keyofAndIndexedAccessErrors.ts, 152, 1))
+>T : Symbol(T, Decl(keyofAndIndexedAccessErrors.ts, 156, 11))
+>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
+
+  testy: T;
+>testy : Symbol(Test.testy, Decl(keyofAndIndexedAccessErrors.ts, 156, 46))
+>T : Symbol(T, Decl(keyofAndIndexedAccessErrors.ts, 156, 11))
+
+  constructor(t: T) {
+>t : Symbol(t, Decl(keyofAndIndexedAccessErrors.ts, 159, 14))
+>T : Symbol(T, Decl(keyofAndIndexedAccessErrors.ts, 156, 11))
+
+    this.testy = t;
+>this.testy : Symbol(Test.testy, Decl(keyofAndIndexedAccessErrors.ts, 156, 46))
+>this : Symbol(Test, Decl(keyofAndIndexedAccessErrors.ts, 152, 1))
+>testy : Symbol(Test.testy, Decl(keyofAndIndexedAccessErrors.ts, 156, 46))
+>t : Symbol(t, Decl(keyofAndIndexedAccessErrors.ts, 159, 14))
+  }
+
+  public t(key: keyof T): number {
+>t : Symbol(Test.t, Decl(keyofAndIndexedAccessErrors.ts, 161, 3))
+>key : Symbol(key, Decl(keyofAndIndexedAccessErrors.ts, 163, 11))
+>T : Symbol(T, Decl(keyofAndIndexedAccessErrors.ts, 156, 11))
+
+    this.testy[key] += 1; // Error
+>this.testy : Symbol(Test.testy, Decl(keyofAndIndexedAccessErrors.ts, 156, 46))
+>this : Symbol(Test, Decl(keyofAndIndexedAccessErrors.ts, 152, 1))
+>testy : Symbol(Test.testy, Decl(keyofAndIndexedAccessErrors.ts, 156, 46))
+>key : Symbol(key, Decl(keyofAndIndexedAccessErrors.ts, 163, 11))
+
+    return this.testy[key];
+>this.testy : Symbol(Test.testy, Decl(keyofAndIndexedAccessErrors.ts, 156, 46))
+>this : Symbol(Test, Decl(keyofAndIndexedAccessErrors.ts, 152, 1))
+>testy : Symbol(Test.testy, Decl(keyofAndIndexedAccessErrors.ts, 156, 46))
+>key : Symbol(key, Decl(keyofAndIndexedAccessErrors.ts, 163, 11))
+  }
+}
+

tests/baselines/reference/keyofAndIndexedAccessErrors.types

@@ -483,3 +483,44 @@ function f31<T, K extends keyof T>() {
 >"hello" : "hello"
 }
 
+// Repro from #51069
+
+class Test<T extends Record<string, number>> {
+>Test : Test<T>
+
+  testy: T;
+>testy : T
+
+  constructor(t: T) {
+>t : T
+
+    this.testy = t;
+>this.testy = t : T
+>this.testy : T
+>this : this
+>testy : T
+>t : T
+  }
+
+  public t(key: keyof T): number {
+>t : (key: keyof T) => number
+>key : keyof T
+
+    this.testy[key] += 1; // Error
+>this.testy[key] += 1 : number
+>this.testy[key] : T[keyof T]
+>this.testy : T
+>this : this
+>testy : T
+>key : keyof T
+>1 : 1
+
+    return this.testy[key];
+>this.testy[key] : T[keyof T]
+>this.testy : T
+>this : this
+>testy : T
+>key : keyof T
+  }
+}
+