Combine keyof T inferences (#22525)

* Combine keyof T inferences

* Extract covariant inference derivation into function

* Test:keyof inference lower priority than return inference

for #22376

* Update 'expected' comment in keyofInferenceLowerPriorityThanReturn

* Update comment in test too, not just baselines

* Fix typo

* Move tests

tests/cases/conformance/types/typeRelationships/typeInference/keyofInferenceIntersectsResults.ts

@@ -0,0 +1,11 @@
+interface X {
+    a: string;
+    b: string;
+}
+
+declare function foo<T = X>(x: keyof T, y: keyof T): T;
+declare function bar<T>(x: keyof T, y: keyof T): T;
+
+const a = foo<X>('a', 'b'); // compiles cleanly
+const b = foo('a', 'b');    // also clean
+const c = bar('a', 'b');    // still clean

tests/cases/conformance/types/typeRelationships/typeInference/keyofInferenceLowerPriorityThanReturn.ts

@@ -0,0 +1,46 @@
+// #22736
+declare class Write {
+    protected dummy: Write;
+}
+
+declare class Col<s, a> {
+    protected dummy: [Col<s, a>, s, a];
+}
+
+declare class Table<Req, Def> {
+    protected dummy: [Table<Req, Def>, Req, Def];
+}
+
+type MakeTable<T1 extends object, T2 extends object> = {
+    [P in keyof T1]: Col<Write, T1[P]>;
+} & {
+        [P in keyof T2]: Col<Write, T2[P]>;
+    };
+
+declare class ConflictTarget<Cols> {
+    public static tableColumns<Cols>(cols: (keyof Cols)[]): ConflictTarget<Cols>;
+    protected dummy: [ConflictTarget<Cols>, Cols];
+}
+
+
+
+const bookTable: Table<BookReq, BookDef> = null as any
+
+interface BookReq {
+    readonly title: string;
+    readonly serial: number;
+}
+
+interface BookDef {
+    readonly author: string;
+    readonly numPages: number | null;
+}
+
+
+function insertOnConflictDoNothing<Req extends object, Def extends object>(_table: Table<Req, Def>, _conflictTarget: ConflictTarget<Req & Def>): boolean {
+    throw new Error();
+}
+
+function f() {
+    insertOnConflictDoNothing(bookTable, ConflictTarget.tableColumns(["serial"]));  // <-- No error here; should use the type inferred for the return type of `tableColumns`
+}