Merge pull request #30917 from Microsoft/fixIntersectionUnionConstraint

Fix checking of intersection with union constraint

Author: ahejlsberg

src/compiler/checker.ts

@@ -7598,11 +7598,6 @@ namespace ts {
                         constraint = getConstraintOfType(constraint);
                     }
                     if (constraint) {
-                        // A constraint that isn't a union type implies that the final type would be a non-union
-                        // type as well. Since non-union constraints are of no interest, we can exit here.
-                        if (!(constraint.flags & TypeFlags.Union)) {
-                            return undefined;
-                        }
                         constraints = append(constraints, constraint);
                     }
                 }

tests/baselines/reference/intersectionWithUnionConstraint.errors.txt

@@ -80,4 +80,9 @@ tests/cases/conformance/types/intersection/intersectionWithUnionConstraint.ts(12
 
     type UnexpectedError<T extends PropertyKey> = T
     type NoErrorHere<T extends PropertyKey> = T
+    
+    // Repro from #30331
+    
+    type a<T> = T extends Array<infer U> ? U : never;
+    type b<T> = { [K in a<T> & keyof T ]: 42 };
 

tests/baselines/reference/intersectionWithUnionConstraint.js

@@ -33,6 +33,11 @@ type Example<T, U> = { [K in keyof T]: K extends keyof U ? UnexpectedError<K> :
 
 type UnexpectedError<T extends PropertyKey> = T
 type NoErrorHere<T extends PropertyKey> = T
+
+// Repro from #30331
+
+type a<T> = T extends Array<infer U> ? U : never;
+type b<T> = { [K in a<T> & keyof T ]: 42 };
 
 
 //// [intersectionWithUnionConstraint.js]

tests/baselines/reference/intersectionWithUnionConstraint.symbols

@@ -112,3 +112,21 @@ type NoErrorHere<T extends PropertyKey> = T
 >PropertyKey : Symbol(PropertyKey, Decl(lib.es5.d.ts, --, --))
 >T : Symbol(T, Decl(intersectionWithUnionConstraint.ts, 33, 17))
 
+// Repro from #30331
+
+type a<T> = T extends Array<infer U> ? U : never;
+>a : Symbol(a, Decl(intersectionWithUnionConstraint.ts, 33, 43))
+>T : Symbol(T, Decl(intersectionWithUnionConstraint.ts, 37, 7))
+>T : Symbol(T, Decl(intersectionWithUnionConstraint.ts, 37, 7))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>U : Symbol(U, Decl(intersectionWithUnionConstraint.ts, 37, 33))
+>U : Symbol(U, Decl(intersectionWithUnionConstraint.ts, 37, 33))
+
+type b<T> = { [K in a<T> & keyof T ]: 42 };
+>b : Symbol(b, Decl(intersectionWithUnionConstraint.ts, 37, 49))
+>T : Symbol(T, Decl(intersectionWithUnionConstraint.ts, 38, 7))
+>K : Symbol(K, Decl(intersectionWithUnionConstraint.ts, 38, 15))
+>a : Symbol(a, Decl(intersectionWithUnionConstraint.ts, 33, 43))
+>T : Symbol(T, Decl(intersectionWithUnionConstraint.ts, 38, 7))
+>T : Symbol(T, Decl(intersectionWithUnionConstraint.ts, 38, 7))
+

tests/baselines/reference/intersectionWithUnionConstraint.types

@@ -84,3 +84,11 @@ type UnexpectedError<T extends PropertyKey> = T
 type NoErrorHere<T extends PropertyKey> = T
 >NoErrorHere : T
 
+// Repro from #30331
+
+type a<T> = T extends Array<infer U> ? U : never;
+>a : a<T>
+
+type b<T> = { [K in a<T> & keyof T ]: 42 };
+>b : b<T>
+

tests/cases/conformance/types/intersection/intersectionWithUnionConstraint.ts

@@ -34,3 +34,8 @@ type Example<T, U> = { [K in keyof T]: K extends keyof U ? UnexpectedError<K> :
 
 type UnexpectedError<T extends PropertyKey> = T
 type NoErrorHere<T extends PropertyKey> = T
+
+// Repro from #30331
+
+type a<T> = T extends Array<infer U> ? U : never;
+type b<T> = { [K in a<T> & keyof T ]: 42 };