Add regression tests

Author: ahejlsberg

tests/baselines/reference/indexedAccessConstraints.errors.txt

@@ -0,0 +1,31 @@
+indexedAccessConstraints.ts(2,9): error TS2322: Type 'T[keyof T]' is not assignable to type 'number'.
+  Type 'T[string] | T[number] | T[symbol]' is not assignable to type 'number'.
+    Type 'T[string]' is not assignable to type 'number'.
+
+
+==== indexedAccessConstraints.ts (1 errors) ====
+    function foo<T extends object>(a: T[keyof T]) {
+        let b: number = a;  // Error
+            ~
+!!! error TS2322: Type 'T[keyof T]' is not assignable to type 'number'.
+!!! error TS2322:   Type 'T[string] | T[number] | T[symbol]' is not assignable to type 'number'.
+!!! error TS2322:     Type 'T[string]' is not assignable to type 'number'.
+    }
+    
+    // Repro from #54522
+    
+    export function methodFnLength<T extends {}, K extends keyof T>(obj: T, methodKey: K): number {
+        const fn = obj[methodKey];
+        if (typeof fn !== 'function') {
+            return 0;
+        }
+        return fn.length;
+    }
+    
+    // Repro from #54837
+    
+    function getField<T extends object>(x: T | null, k: keyof T) {
+        const result = x ? x[k] : null;
+        return result;  // T[keyof T] | null
+    }
+    

tests/baselines/reference/indexedAccessConstraints.symbols

@@ -0,0 +1,63 @@
+//// [tests/cases/compiler/indexedAccessConstraints.ts] ////
+
+=== indexedAccessConstraints.ts ===
+function foo<T extends object>(a: T[keyof T]) {
+>foo : Symbol(foo, Decl(indexedAccessConstraints.ts, 0, 0))
+>T : Symbol(T, Decl(indexedAccessConstraints.ts, 0, 13))
+>a : Symbol(a, Decl(indexedAccessConstraints.ts, 0, 31))
+>T : Symbol(T, Decl(indexedAccessConstraints.ts, 0, 13))
+>T : Symbol(T, Decl(indexedAccessConstraints.ts, 0, 13))
+
+    let b: number = a;  // Error
+>b : Symbol(b, Decl(indexedAccessConstraints.ts, 1, 7))
+>a : Symbol(a, Decl(indexedAccessConstraints.ts, 0, 31))
+}
+
+// Repro from #54522
+
+export function methodFnLength<T extends {}, K extends keyof T>(obj: T, methodKey: K): number {
+>methodFnLength : Symbol(methodFnLength, Decl(indexedAccessConstraints.ts, 2, 1))
+>T : Symbol(T, Decl(indexedAccessConstraints.ts, 6, 31))
+>K : Symbol(K, Decl(indexedAccessConstraints.ts, 6, 44))
+>T : Symbol(T, Decl(indexedAccessConstraints.ts, 6, 31))
+>obj : Symbol(obj, Decl(indexedAccessConstraints.ts, 6, 64))
+>T : Symbol(T, Decl(indexedAccessConstraints.ts, 6, 31))
+>methodKey : Symbol(methodKey, Decl(indexedAccessConstraints.ts, 6, 71))
+>K : Symbol(K, Decl(indexedAccessConstraints.ts, 6, 44))
+
+    const fn = obj[methodKey];
+>fn : Symbol(fn, Decl(indexedAccessConstraints.ts, 7, 9))
+>obj : Symbol(obj, Decl(indexedAccessConstraints.ts, 6, 64))
+>methodKey : Symbol(methodKey, Decl(indexedAccessConstraints.ts, 6, 71))
+
+    if (typeof fn !== 'function') {
+>fn : Symbol(fn, Decl(indexedAccessConstraints.ts, 7, 9))
+
+        return 0;
+    }
+    return fn.length;
+>fn.length : Symbol(Function.length, Decl(lib.es5.d.ts, --, --))
+>fn : Symbol(fn, Decl(indexedAccessConstraints.ts, 7, 9))
+>length : Symbol(Function.length, Decl(lib.es5.d.ts, --, --))
+}
+
+// Repro from #54837
+
+function getField<T extends object>(x: T | null, k: keyof T) {
+>getField : Symbol(getField, Decl(indexedAccessConstraints.ts, 12, 1))
+>T : Symbol(T, Decl(indexedAccessConstraints.ts, 16, 18))
+>x : Symbol(x, Decl(indexedAccessConstraints.ts, 16, 36))
+>T : Symbol(T, Decl(indexedAccessConstraints.ts, 16, 18))
+>k : Symbol(k, Decl(indexedAccessConstraints.ts, 16, 48))
+>T : Symbol(T, Decl(indexedAccessConstraints.ts, 16, 18))
+
+    const result = x ? x[k] : null;
+>result : Symbol(result, Decl(indexedAccessConstraints.ts, 17, 9))
+>x : Symbol(x, Decl(indexedAccessConstraints.ts, 16, 36))
+>x : Symbol(x, Decl(indexedAccessConstraints.ts, 16, 36))
+>k : Symbol(k, Decl(indexedAccessConstraints.ts, 16, 48))
+
+    return result;  // T[keyof T] | null
+>result : Symbol(result, Decl(indexedAccessConstraints.ts, 17, 9))
+}
+

tests/baselines/reference/indexedAccessConstraints.types

@@ -0,0 +1,59 @@
+//// [tests/cases/compiler/indexedAccessConstraints.ts] ////
+
+=== indexedAccessConstraints.ts ===
+function foo<T extends object>(a: T[keyof T]) {
+>foo : <T extends object>(a: T[keyof T]) => void
+>a : T[keyof T]
+
+    let b: number = a;  // Error
+>b : number
+>a : T[keyof T]
+}
+
+// Repro from #54522
+
+export function methodFnLength<T extends {}, K extends keyof T>(obj: T, methodKey: K): number {
+>methodFnLength : <T extends {}, K extends keyof T>(obj: T, methodKey: K) => number
+>obj : T
+>methodKey : K
+
+    const fn = obj[methodKey];
+>fn : T[K]
+>obj[methodKey] : T[K]
+>obj : T
+>methodKey : K
+
+    if (typeof fn !== 'function') {
+>typeof fn !== 'function' : boolean
+>typeof fn : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
+>fn : T[K]
+>'function' : "function"
+
+        return 0;
+>0 : 0
+    }
+    return fn.length;
+>fn.length : number
+>fn : T[K] & Function
+>length : number
+}
+
+// Repro from #54837
+
+function getField<T extends object>(x: T | null, k: keyof T) {
+>getField : <T extends object>(x: T | null, k: keyof T) => T[keyof T] | null
+>x : T | null
+>k : keyof T
+
+    const result = x ? x[k] : null;
+>result : T[keyof T] | null
+>x ? x[k] : null : T[keyof T] | null
+>x : T | null
+>x[k] : T[keyof T]
+>x : T
+>k : keyof T
+
+    return result;  // T[keyof T] | null
+>result : T[keyof T] | null
+}
+

tests/cases/compiler/indexedAccessConstraints.ts

@@ -0,0 +1,23 @@
+// @strict: true
+// @noEmit: true
+
+function foo<T extends object>(a: T[keyof T]) {
+    let b: number = a;  // Error
+}
+
+// Repro from #54522
+
+export function methodFnLength<T extends {}, K extends keyof T>(obj: T, methodKey: K): number {
+    const fn = obj[methodKey];
+    if (typeof fn !== 'function') {
+        return 0;
+    }
+    return fn.length;
+}
+
+// Repro from #54837
+
+function getField<T extends object>(x: T | null, k: keyof T) {
+    const result = x ? x[k] : null;
+    return result;  // T[keyof T] | null
+}