Cherry-pick PR #50620 into release-4.8 (#50676)

Component commits:
4635cdc Forward intersection state flag to conditional type target check

Co-authored-by: Andrew Branch <andrew@wheream.io>

src/compiler/checker.ts

@@ -19788,8 +19788,8 @@ namespace ts {
                         const skipTrue = !isTypeAssignableTo(getPermissiveInstantiation(c.checkType), getPermissiveInstantiation(c.extendsType));
                         const skipFalse = !skipTrue && isTypeAssignableTo(getRestrictiveInstantiation(c.checkType), getRestrictiveInstantiation(c.extendsType));
                         // TODO: Find a nice way to include potential conditional type breakdowns in error output, if they seem good (they usually don't)
-                        if (result = skipTrue ? Ternary.True : isRelatedTo(source, getTrueTypeFromConditionalType(c), RecursionFlags.Target, /*reportErrors*/ false)) {
-                            result &= skipFalse ? Ternary.True : isRelatedTo(source, getFalseTypeFromConditionalType(c), RecursionFlags.Target, /*reportErrors*/ false);
+                        if (result = skipTrue ? Ternary.True : isRelatedTo(source, getTrueTypeFromConditionalType(c), RecursionFlags.Target, /*reportErrors*/ false, /*headMessage*/ undefined, intersectionState)) {
+                            result &= skipFalse ? Ternary.True : isRelatedTo(source, getFalseTypeFromConditionalType(c), RecursionFlags.Target, /*reportErrors*/ false, /*headMessage*/ undefined, intersectionState);
                             if (result) {
                                 return result;
                             }

tests/baselines/reference/excessPropertyCheckingIntersectionWithConditional.js

@@ -0,0 +1,10 @@
+//// [excessPropertyCheckingIntersectionWithConditional.ts]
+type Foo<K> = K extends unknown ? { a: number } : unknown
+const createDefaultExample = <K,>(x: K): Foo<K> & { x: K; } => {
+  return { a: 1, x: x }; // okay in TS 4.7.4, error in TS 4.8.2
+}
+
+//// [excessPropertyCheckingIntersectionWithConditional.js]
+var createDefaultExample = function (x) {
+    return { a: 1, x: x }; // okay in TS 4.7.4, error in TS 4.8.2
+};

tests/baselines/reference/excessPropertyCheckingIntersectionWithConditional.symbols

@@ -0,0 +1,22 @@
+=== tests/cases/compiler/excessPropertyCheckingIntersectionWithConditional.ts ===
+type Foo<K> = K extends unknown ? { a: number } : unknown
+>Foo : Symbol(Foo, Decl(excessPropertyCheckingIntersectionWithConditional.ts, 0, 0))
+>K : Symbol(K, Decl(excessPropertyCheckingIntersectionWithConditional.ts, 0, 9))
+>K : Symbol(K, Decl(excessPropertyCheckingIntersectionWithConditional.ts, 0, 9))
+>a : Symbol(a, Decl(excessPropertyCheckingIntersectionWithConditional.ts, 0, 35))
+
+const createDefaultExample = <K,>(x: K): Foo<K> & { x: K; } => {
+>createDefaultExample : Symbol(createDefaultExample, Decl(excessPropertyCheckingIntersectionWithConditional.ts, 1, 5))
+>K : Symbol(K, Decl(excessPropertyCheckingIntersectionWithConditional.ts, 1, 30))
+>x : Symbol(x, Decl(excessPropertyCheckingIntersectionWithConditional.ts, 1, 34))
+>K : Symbol(K, Decl(excessPropertyCheckingIntersectionWithConditional.ts, 1, 30))
+>Foo : Symbol(Foo, Decl(excessPropertyCheckingIntersectionWithConditional.ts, 0, 0))
+>K : Symbol(K, Decl(excessPropertyCheckingIntersectionWithConditional.ts, 1, 30))
+>x : Symbol(x, Decl(excessPropertyCheckingIntersectionWithConditional.ts, 1, 51))
+>K : Symbol(K, Decl(excessPropertyCheckingIntersectionWithConditional.ts, 1, 30))
+
+  return { a: 1, x: x }; // okay in TS 4.7.4, error in TS 4.8.2
+>a : Symbol(a, Decl(excessPropertyCheckingIntersectionWithConditional.ts, 2, 10))
+>x : Symbol(x, Decl(excessPropertyCheckingIntersectionWithConditional.ts, 2, 16))
+>x : Symbol(x, Decl(excessPropertyCheckingIntersectionWithConditional.ts, 1, 34))
+}

tests/baselines/reference/excessPropertyCheckingIntersectionWithConditional.types

@@ -0,0 +1,18 @@
+=== tests/cases/compiler/excessPropertyCheckingIntersectionWithConditional.ts ===
+type Foo<K> = K extends unknown ? { a: number } : unknown
+>Foo : Foo<K>
+>a : number
+
+const createDefaultExample = <K,>(x: K): Foo<K> & { x: K; } => {
+>createDefaultExample : <K>(x: K) => Foo<K> & { x: K; }
+><K,>(x: K): Foo<K> & { x: K; } => {  return { a: 1, x: x }; // okay in TS 4.7.4, error in TS 4.8.2} : <K>(x: K) => Foo<K> & { x: K; }
+>x : K
+>x : K
+
+  return { a: 1, x: x }; // okay in TS 4.7.4, error in TS 4.8.2
+>{ a: 1, x: x } : { a: number; x: K; }
+>a : number
+>1 : 1
+>x : K
+>x : K
+}

tests/cases/compiler/excessPropertyCheckingIntersectionWithConditional.ts

@@ -0,0 +1,4 @@
+type Foo<K> = K extends unknown ? { a: number } : unknown
+const createDefaultExample = <K,>(x: K): Foo<K> & { x: K; } => {
+  return { a: 1, x: x }; // okay in TS 4.7.4, error in TS 4.8.2
+}