Add regression tests

Author: ahejlsberg

tests/baselines/reference/mappedTypeErrors2.errors.txt

@@ -0,0 +1,35 @@
+tests/cases/conformance/types/mapped/mappedTypeErrors2.ts(9,30): error TS2536: Type 'K' cannot be used to index type 'T1<K>'.
+tests/cases/conformance/types/mapped/mappedTypeErrors2.ts(13,30): error TS2536: Type 'K' cannot be used to index type 'T3'.
+tests/cases/conformance/types/mapped/mappedTypeErrors2.ts(15,47): error TS2536: Type 'S' cannot be used to index type 'AB'.
+tests/cases/conformance/types/mapped/mappedTypeErrors2.ts(17,49): error TS2536: Type 'L' cannot be used to index type '{ [key in AB[S]]: true; }'.
+
+
+==== tests/cases/conformance/types/mapped/mappedTypeErrors2.ts (4 errors) ====
+    // Repros from #17238
+    
+    type AB = {
+        a: 'a'
+        b: 'a'
+    };
+    
+    type T1<K extends keyof AB> = { [key in AB[K]]: true };
+    type T2<K extends 'a'|'b'> = T1<K>[K]; // Error
+                                 ~~~~~~~~
+!!! error TS2536: Type 'K' cannot be used to index type 'T1<K>'.
+    
+    type R = AB[keyof AB]; // "a"
+    type T3 = { [key in R]: true };
+    type T4<K extends 'a'|'b'> = T3[K] // Error
+                                 ~~~~~
+!!! error TS2536: Type 'K' cannot be used to index type 'T3'.
+    
+    type T5<S extends 'a'|'b'|'extra'> = {[key in AB[S]]: true}[S]; // Error
+                                                  ~~~~~
+!!! error TS2536: Type 'S' cannot be used to index type 'AB'.
+    
+    type T6<S extends 'a'|'b', L extends 'a'|'b'> = {[key in AB[S]]: true}[L]; // Error
+                                                    ~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2536: Type 'L' cannot be used to index type '{ [key in AB[S]]: true; }'.
+    
+    type T7<S extends 'a'|'b', L extends 'a'> = {[key in AB[S]]: true}[L];
+    

tests/baselines/reference/mappedTypeErrors2.js

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+//// [mappedTypeErrors2.ts]
+// Repros from #17238
+
+type AB = {
+    a: 'a'
+    b: 'a'
+};
+
+type T1<K extends keyof AB> = { [key in AB[K]]: true };
+type T2<K extends 'a'|'b'> = T1<K>[K]; // Error
+
+type R = AB[keyof AB]; // "a"
+type T3 = { [key in R]: true };
+type T4<K extends 'a'|'b'> = T3[K] // Error
+
+type T5<S extends 'a'|'b'|'extra'> = {[key in AB[S]]: true}[S]; // Error
+
+type T6<S extends 'a'|'b', L extends 'a'|'b'> = {[key in AB[S]]: true}[L]; // Error
+
+type T7<S extends 'a'|'b', L extends 'a'> = {[key in AB[S]]: true}[L];
+
+
+//// [mappedTypeErrors2.js]
+// Repros from #17238
+
+
+//// [mappedTypeErrors2.d.ts]
+declare type AB = {
+    a: 'a';
+    b: 'a';
+};
+declare type T1<K extends keyof AB> = {
+    [key in AB[K]]: true;
+};
+declare type T2<K extends 'a' | 'b'> = T1<K>[K];
+declare type R = AB[keyof AB];
+declare type T3 = {
+    [key in R]: true;
+};
+declare type T4<K extends 'a' | 'b'> = T3[K];
+declare type T5<S extends 'a' | 'b' | 'extra'> = {
+    [key in AB[S]]: true;
+}[S];
+declare type T6<S extends 'a' | 'b', L extends 'a' | 'b'> = {
+    [key in AB[S]]: true;
+}[L];
+declare type T7<S extends 'a' | 'b', L extends 'a'> = {
+    [key in AB[S]]: true;
+}[L];

tests/cases/conformance/types/mapped/mappedTypeErrors2.ts

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+// @strictNullChecks: true
+// @declaration: true
+
+// Repros from #17238
+
+type AB = {
+    a: 'a'
+    b: 'a'
+};
+
+type T1<K extends keyof AB> = { [key in AB[K]]: true };
+type T2<K extends 'a'|'b'> = T1<K>[K]; // Error
+
+type R = AB[keyof AB]; // "a"
+type T3 = { [key in R]: true };
+type T4<K extends 'a'|'b'> = T3[K] // Error
+
+type T5<S extends 'a'|'b'|'extra'> = {[key in AB[S]]: true}[S]; // Error
+
+type T6<S extends 'a'|'b', L extends 'a'|'b'> = {[key in AB[S]]: true}[L]; // Error
+
+type T7<S extends 'a'|'b', L extends 'a'> = {[key in AB[S]]: true}[L];