Preserve generic substitutions through instantiation more often

src/compiler/checker.ts

@@ -19053,7 +19053,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             if (newConstraint.flags & TypeFlags.AnyOrUnknown || isTypeAssignableTo(getRestrictiveInstantiation(newBaseType), getRestrictiveInstantiation(newConstraint))) {
                 return newBaseType;
             }
-            return newBaseType.flags & TypeFlags.TypeVariable ? getSubstitutionType(newBaseType, newConstraint) : getIntersectionType([newConstraint, newBaseType]);
+            return (newBaseType.flags & TypeFlags.TypeVariable || newConstraint.flags & TypeFlags.TypeVariable) ? getSubstitutionType(newBaseType, newConstraint) : getIntersectionType([newConstraint, newBaseType]);
         }
         return type;
     }

tests/baselines/reference/callOfConditionalTypeWithConcreteBranches.types

@@ -64,11 +64,11 @@ function fn2<T>(arg: Q2<T>) {
   arg(arg => useT(arg));
 >arg(arg => useT(arg)) : void
 >arg : Q2<T>
->arg => useT(arg) : (arg: T & number) => void
->arg : T & number
+>arg => useT(arg) : (arg: number) => void
+>arg : number
 >useT(arg) : void
 >useT : (_arg: T) => void
->arg : T & number
+>arg : number
 }
 // Legal invocations are not problematic
 fn2<string | number>(m => m(42));

tests/baselines/reference/conditionalSubstitutionInferencesLowerPriority.js

@@ -0,0 +1,23 @@
+//// [conditionalSubstitutionInferencesLowerPriority.ts]
+type TestType<Keys extends string> = string extends Keys ? Record<Keys, string> : Record<Keys, string>
+
+function inferHelper<Keys extends string>(data: TestType<Keys>) {
+    return data;
+}
+
+export const a = inferHelper({
+    // key1 is inferred to be value1 here
+    key1: "value1"
+})
+
+//// [conditionalSubstitutionInferencesLowerPriority.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.a = void 0;
+function inferHelper(data) {
+    return data;
+}
+exports.a = inferHelper({
+    // key1 is inferred to be value1 here
+    key1: "value1"
+});

tests/baselines/reference/conditionalSubstitutionInferencesLowerPriority.symbols

@@ -0,0 +1,30 @@
+=== tests/cases/compiler/conditionalSubstitutionInferencesLowerPriority.ts ===
+type TestType<Keys extends string> = string extends Keys ? Record<Keys, string> : Record<Keys, string>
+>TestType : Symbol(TestType, Decl(conditionalSubstitutionInferencesLowerPriority.ts, 0, 0))
+>Keys : Symbol(Keys, Decl(conditionalSubstitutionInferencesLowerPriority.ts, 0, 14))
+>Keys : Symbol(Keys, Decl(conditionalSubstitutionInferencesLowerPriority.ts, 0, 14))
+>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
+>Keys : Symbol(Keys, Decl(conditionalSubstitutionInferencesLowerPriority.ts, 0, 14))
+>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
+>Keys : Symbol(Keys, Decl(conditionalSubstitutionInferencesLowerPriority.ts, 0, 14))
+
+function inferHelper<Keys extends string>(data: TestType<Keys>) {
+>inferHelper : Symbol(inferHelper, Decl(conditionalSubstitutionInferencesLowerPriority.ts, 0, 102))
+>Keys : Symbol(Keys, Decl(conditionalSubstitutionInferencesLowerPriority.ts, 2, 21))
+>data : Symbol(data, Decl(conditionalSubstitutionInferencesLowerPriority.ts, 2, 42))
+>TestType : Symbol(TestType, Decl(conditionalSubstitutionInferencesLowerPriority.ts, 0, 0))
+>Keys : Symbol(Keys, Decl(conditionalSubstitutionInferencesLowerPriority.ts, 2, 21))
+
+    return data;
+>data : Symbol(data, Decl(conditionalSubstitutionInferencesLowerPriority.ts, 2, 42))
+}
+
+export const a = inferHelper({
+>a : Symbol(a, Decl(conditionalSubstitutionInferencesLowerPriority.ts, 6, 12))
+>inferHelper : Symbol(inferHelper, Decl(conditionalSubstitutionInferencesLowerPriority.ts, 0, 102))
+
+    // key1 is inferred to be value1 here
+    key1: "value1"
+>key1 : Symbol(key1, Decl(conditionalSubstitutionInferencesLowerPriority.ts, 6, 30))
+
+})

tests/baselines/reference/conditionalSubstitutionInferencesLowerPriority.types

@@ -0,0 +1,24 @@
+=== tests/cases/compiler/conditionalSubstitutionInferencesLowerPriority.ts ===
+type TestType<Keys extends string> = string extends Keys ? Record<Keys, string> : Record<Keys, string>
+>TestType : TestType<Keys>
+
+function inferHelper<Keys extends string>(data: TestType<Keys>) {
+>inferHelper : <Keys extends string>(data: TestType<Keys>) => TestType<Keys>
+>data : TestType<Keys>
+
+    return data;
+>data : TestType<Keys>
+}
+
+export const a = inferHelper({
+>a : Record<"key1", string>
+>inferHelper({    // key1 is inferred to be value1 here    key1: "value1"}) : Record<"key1", string>
+>inferHelper : <Keys extends string>(data: TestType<Keys>) => TestType<Keys>
+>{    // key1 is inferred to be value1 here    key1: "value1"} : { key1: string; }
+
+    // key1 is inferred to be value1 here
+    key1: "value1"
+>key1 : string
+>"value1" : "value1"
+
+})

tests/cases/compiler/conditionalSubstitutionInferencesLowerPriority.ts

@@ -0,0 +1,10 @@
+type TestType<Keys extends string> = string extends Keys ? Record<Keys, string> : Record<Keys, string>
+
+function inferHelper<Keys extends string>(data: TestType<Keys>) {
+    return data;
+}
+
+export const a = inferHelper({
+    // key1 is inferred to be value1 here
+    key1: "value1"
+})