Merge pull request #26140 from Kingwl/completionUnionType

improve completions for union type in type arguments

Author: sheetalkamat

src/services/completions.ts

@@ -402,6 +402,8 @@ namespace ts.Completions {
                         return stringLiteralCompletionsFromProperties(typeChecker.getTypeFromTypeNode((node.parent.parent as IndexedAccessTypeNode).objectType));
                     case SyntaxKind.ImportType:
                         return { kind: StringLiteralCompletionKind.Paths, paths: PathCompletions.getStringLiteralCompletionsFromModuleNames(sourceFile, node, compilerOptions, host, typeChecker) };
+                    case SyntaxKind.UnionType:
+                        return isTypeReferenceNode(node.parent.parent.parent) ? { kind: StringLiteralCompletionKind.Types, types: getStringLiteralTypes(typeChecker.getTypeArgumentConstraint(node.parent.parent as UnionTypeNode)), isNewIdentifier: false } : undefined;
                     default:
                         return undefined;
                 }

tests/cases/fourslash/completionListForStringUnion.ts

@@ -0,0 +1,12 @@
+/// <reference path='fourslash.ts' />
+
+//// type A = 'fooooo' | 'barrrrr';
+//// type B<T extends A> = {};
+//// type C = B<'fooooo' | '/**/'>
+
+
+goTo.marker();
+verify.completionListContains("fooooo");
+verify.completionListContains("barrrrr");
+edit.insert("b");
+verify.completionListContains("barrrrr");