Merge pull request #23768 from Microsoft/fixIndexedAccessAssignability

Fix assignability of unconstrained T[K]

Author: ahejlsberg

src/compiler/checker.ts

@@ -10670,23 +10670,8 @@ namespace ts {
                     }
                 }
 
-                if (source.flags & TypeFlags.TypeParameter) {
-                    let constraint = getConstraintForRelation(<TypeParameter>source);
-                    // A type parameter with no constraint is not related to the non-primitive object type.
-                    if (constraint || !(target.flags & TypeFlags.NonPrimitive)) {
-                        if (!constraint || constraint.flags & TypeFlags.Any) {
-                            constraint = emptyObjectType;
-                        }
-                        // Report constraint errors only if the constraint is not the empty object type
-                        const reportConstraintErrors = reportErrors && constraint !== emptyObjectType;
-                        if (result = isRelatedTo(constraint, target, reportConstraintErrors)) {
-                            errorInfo = saveErrorInfo;
-                            return result;
-                        }
-                    }
-                }
-                else if (source.flags & TypeFlags.IndexedAccess) {
-                    if (target.flags & TypeFlags.IndexedAccess) {
+                if (source.flags & TypeFlags.TypeVariable) {
+                    if (source.flags & TypeFlags.IndexedAccess && target.flags & TypeFlags.IndexedAccess) {
                         // A type S[K] is related to a type T[J] if S is related to T and K is related to J.
                         if (result = isRelatedTo((<IndexedAccessType>source).objectType, (<IndexedAccessType>target).objectType, reportErrors)) {
                             result &= isRelatedTo((<IndexedAccessType>source).indexType, (<IndexedAccessType>target).indexType, reportErrors);
@@ -10696,11 +10681,15 @@ namespace ts {
                             return result;
                         }
                     }
-                    // A type S[K] is related to a type T if C is related to T, where C is the
-                    // constraint of S[K].
-                    const constraint = getConstraintForRelation(<IndexedAccessType>source);
-                    if (constraint) {
-                        if (result = isRelatedTo(constraint, target, reportErrors)) {
+                    let constraint = getConstraintForRelation(<TypeParameter>source);
+                    // A type variable with no constraint is not related to the non-primitive object type.
+                    if (constraint || !(target.flags & TypeFlags.NonPrimitive)) {
+                        if (!constraint || constraint.flags & TypeFlags.Any) {
+                            constraint = emptyObjectType;
+                        }
+                        // Report constraint errors only if the constraint is not the empty object type
+                        const reportConstraintErrors = reportErrors && constraint !== emptyObjectType;
+                        if (result = isRelatedTo(constraint, target, reportConstraintErrors)) {
                             errorInfo = saveErrorInfo;
                             return result;
                         }

tests/baselines/reference/keyofAndIndexedAccess.js

@@ -319,6 +319,20 @@ function f90<T extends S2, K extends keyof S2>(x1: S2[keyof S2], x2: T[keyof S2]
     x4.length;
 }
 
+function f91<T, K extends keyof T>(x: T, y: T[keyof T], z: T[K]) {
+    let a: {};
+    a = x;
+    a = y;
+    a = z;
+}
+
+function f92<T, K extends keyof T>(x: T, y: T[keyof T], z: T[K]) {
+    let a: {} | null | undefined;
+    a = x;
+    a = y;
+    a = z;
+}
+
 // Repros from #12011
 
 class Base {
@@ -592,6 +606,27 @@ type DynamicDBRecord<Flag extends string> = ({ dynamicField: number } | { dynami
 function getFlagsFromDynamicRecord<Flag extends string>(record: DynamicDBRecord<Flag>, flags: Flag[]) {
     return record[flags[0]];
 }
+
+// Repro from #21368
+
+interface I {
+    foo: string;
+}
+
+declare function take<T>(p: T): void;
+
+function fn<T extends I, K extends keyof T>(o: T, k: K) {
+    take<{} | null | undefined>(o[k]);
+    take<any>(o[k]);
+}
+
+// Repro from #23133
+
+class Unbounded<T> {
+    foo(x: T[keyof T]) {
+        let y: {} | undefined | null = x;
+    }
+}
 
 
 //// [keyofAndIndexedAccess.js]
@@ -830,6 +865,18 @@ function f90(x1, x2, x3, x4) {
     x3.length;
     x4.length;
 }
+function f91(x, y, z) {
+    var a;
+    a = x;
+    a = y;
+    a = z;
+}
+function f92(x, y, z) {
+    var a;
+    a = x;
+    a = y;
+    a = z;
+}
 // Repros from #12011
 var Base = /** @class */ (function () {
     function Base() {
@@ -986,6 +1033,19 @@ function getFlagsFromSimpleRecord(record, flags) {
 function getFlagsFromDynamicRecord(record, flags) {
     return record[flags[0]];
 }
+function fn(o, k) {
+    take(o[k]);
+    take(o[k]);
+}
+// Repro from #23133
+var Unbounded = /** @class */ (function () {
+    function Unbounded() {
+    }
+    Unbounded.prototype.foo = function (x) {
+        var y = x;
+    };
+    return Unbounded;
+}());
 
 
 //// [keyofAndIndexedAccess.d.ts]
@@ -1126,6 +1186,8 @@ declare type S2 = {
     b: string;
 };
 declare function f90<T extends S2, K extends keyof S2>(x1: S2[keyof S2], x2: T[keyof S2], x3: S2[K], x4: T[K]): void;
+declare function f91<T, K extends keyof T>(x: T, y: T[keyof T], z: T[K]): void;
+declare function f92<T, K extends keyof T>(x: T, y: T[keyof T], z: T[K]): void;
 declare class Base {
     get<K extends keyof this>(prop: K): this[K];
     set<K extends keyof this>(prop: K, value: this[K]): void;
@@ -1298,3 +1360,11 @@ declare type DynamicDBRecord<Flag extends string> = ({
     dynamicField: string;
 }) & DBBoolTable<Flag>;
 declare function getFlagsFromDynamicRecord<Flag extends string>(record: DynamicDBRecord<Flag>, flags: Flag[]): DynamicDBRecord<Flag>[Flag];
+interface I {
+    foo: string;
+}
+declare function take<T>(p: T): void;
+declare function fn<T extends I, K extends keyof T>(o: T, k: K): void;
+declare class Unbounded<T> {
+    foo(x: T[keyof T]): void;
+}