Lazified instantiation of union/intersection types featuring a mapped…

… type
gcnew · Jul 27, 2017 · 73c78e6 · 73c78e6
1 parent d82fd60
commit 73c78e6
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Showing 2 changed files with 28 additions and 4 deletions.
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -7588,7 +7588,7 @@ namespace ts {
             // eagerly using the constraint type of 'this' at the given location.
             if (maybeTypeOfKind(indexType, TypeFlags.TypeVariable | TypeFlags.Index) ||
                 maybeTypeOfKind(objectType, TypeFlags.TypeVariable) && !(accessNode && accessNode.kind === SyntaxKind.ElementAccessExpression) ||
-                isGenericMappedType(objectType)) {
+                maybeTypeOfKind(objectType, isGenericMappedType)) {
                 if (objectType.flags & TypeFlags.Any) {
                     return objectType;
                 }
@@ -16976,14 +16976,18 @@ namespace ts {
 
         // Return true if type might be of the given kind. A union or intersection type might be of a given
         // kind if at least one constituent type is of the given kind.
-        function maybeTypeOfKind(type: Type, kind: TypeFlags): boolean {
-            if (type.flags & kind) {
+        function maybeTypeOfKind(type: Type, kindOrPred: TypeFlags | ((x: Type) => boolean)): boolean {
+            const pred = typeof kindOrPred === 'number'
+                ? (t: Type) => (t.flags & kindOrPred) !== 0
+                : kindOrPred;
+
+            if (pred(type)) {
                 return true;
             }
             if (type.flags & TypeFlags.UnionOrIntersection) {
                 const types = (<UnionOrIntersectionType>type).types;
                 for (const t of types) {
-                    if (maybeTypeOfKind(t, kind)) {
+                    if (maybeTypeOfKind(t, pred)) {
                         return true;
                     }
                 }

diff --git a/tests/cases/conformance/types/mapped/mappedTypesIntersection.ts b/tests/cases/conformance/types/mapped/mappedTypesIntersection.ts
@@ -0,0 +1,20 @@
+// @strictNullChecks: true
+// @declaration: true
+
+type A<T> = ObjectHasKey<T, '0'>
+
+type StringContains<S extends string, L extends string> = ({ [K in S]: 'true' } & {
+  [key: string]: 'false'
+})[L]
+
+type ObjectHasKey<O, L extends string> = StringContains<keyof O, L>
+
+
+type A1<T> = {
+  true: 'true'
+  false: 'false'
+}[ObjectHasKey<T, '1'>]
+
+type B = ObjectHasKey<[string, number], '1'> // B = "true"
+type C = A<[string]> // C = "false"
+type E = A1<[string]>