Add tests

Author: ahejlsberg

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

@@ -0,0 +1,36 @@
+// @strict: true
+
+function f0<T extends { a: string, b: string }>(obj: Pick<T, Extract<keyof T, 'b'>>) {
+    obj.b;
+}
+
+function f1<T extends { a: string, b: string }>(obj: Pick<T, Exclude<keyof T, 'a'>>) {
+    obj.b;
+}
+
+function f2<T extends { a: string, b: string }, U extends { b: string, c: string }>(obj: Pick<T | U, keyof (T | U)>) {
+    obj.b;
+}
+
+function f3<T extends { a: string, b: string }, U extends { b: string, c: string }>(obj: Pick<T & U, keyof (T & U)>) {
+    obj.a;
+    obj.b;
+    obj.c;
+}
+
+function f4<T extends { a: string, b: string }>(obj: Record<Exclude<keyof T, 'b'> | 'c', string>) {
+    obj.a;
+    obj.c;
+}
+
+// Repro from #28821
+
+type TargetProps = {
+    foo: string,
+    bar: string
+};
+
+const modifier = <T extends TargetProps>(targetProps: T) => {
+    let {bar, ...rest} = targetProps;
+    rest.foo;
+};