Fix JSX attribute completion for union types containing string-like t…

src/services/completions.ts

@@ -1860,7 +1860,36 @@ function createCompletionEntry(
             && !(type.flags & TypeFlags.BooleanLike)
             && !(type.flags & TypeFlags.Union && find((type as UnionType).types, type => !!(type.flags & TypeFlags.BooleanLike)))
         ) {
-            if (type.flags & TypeFlags.StringLike || (type.flags & TypeFlags.Union && every((type as UnionType).types, type => !!(type.flags & (TypeFlags.StringLike | TypeFlags.Undefined) || isStringAndEmptyAnonymousObjectIntersection(type))))) {
+            // Check if we should use quotes for string-like types
+            let shouldUseQuotes = false;
+
+            if (type.flags & TypeFlags.StringLike) {
+                // Direct string-like type
+                shouldUseQuotes = true;
+            }
+            else if (type.flags & TypeFlags.Union) {
+                const unionType = type as UnionType;
+                // Check if all types are string-like or undefined (original logic)
+                const allTypesAreStringLikeOrUndefined = every(unionType.types, type => !!(type.flags & (TypeFlags.StringLike | TypeFlags.Undefined) || isStringAndEmptyAnonymousObjectIntersection(type)));
+
+                if (allTypesAreStringLikeOrUndefined) {
+                    shouldUseQuotes = true;
+                }
+                else {
+                    // Check if the union contains string-like types that users would typically provide as strings
+                    // This handles cases like Preact's Signalish<string | undefined> = string | undefined | SignalLike<string | undefined>
+                    const hasStringLikeTypes = some(unionType.types, type => !!(type.flags & TypeFlags.StringLike));
+                    const hasNonObjectTypes = some(unionType.types, type => !!(type.flags & (TypeFlags.StringLike | TypeFlags.Undefined | TypeFlags.Null)));
+
+                    // If the union has string-like types and at least some primitive types (not just objects),
+                    // prefer quotes since users commonly want to provide string values
+                    if (hasStringLikeTypes && hasNonObjectTypes) {
+                        shouldUseQuotes = true;
+                    }
+                }
+            }
+
+            if (shouldUseQuotes) {
                 // If is string like or undefined use quotes
                 insertText = `${escapeSnippetText(name)}=${quote(sourceFile, preferences, "$1")}`;
                 isSnippet = true;

tests/cases/fourslash/jsxAttributeCompletionStyleAutoSignalish.ts

@@ -0,0 +1,52 @@
+/// <reference path="fourslash.ts" />
+
+// @Filename: foo.tsx
+//// declare namespace JSX {
+////     interface Element { }
+////     interface SignalLike<T> {
+////         value: T;
+////         peek(): T;
+////         subscribe(fn: (value: T) => void): () => void;
+////     }
+////     type Signalish<T> = T | SignalLike<T>;
+////     interface IntrinsicElements {
+////         div: {
+////             class?: Signalish<string | undefined>;
+////             id?: Signalish<string | undefined>;
+////             title?: Signalish<string | undefined>;
+////             disabled?: Signalish<boolean | undefined>;
+////             'data-testid'?: Signalish<string | undefined>;
+////             role?: Signalish<string | undefined>;
+////             // For comparison - pure string type should still work
+////             pureString?: string;
+////             // Boolean-like should not get quotes
+////             booleanProp?: boolean;
+////         }
+////     }
+//// }
+////
+//// <div [|prop_/**/|] />
+
+// Test that string-like Signalish types prefer quotes over braces
+verify.completions({
+    marker: "",
+    includes: [
+        {
+            name: "class",
+            insertText: "class=\"$1\"",
+            isSnippet: true,
+            sortText: completion.SortText.OptionalMember,
+        },
+        {
+            name: "id", 
+            insertText: "id=\"$1\"",
+            isSnippet: true,
+            sortText: completion.SortText.OptionalMember,
+        },
+    ],
+    preferences: {
+        jsxAttributeCompletionStyle: "auto",
+        includeCompletionsWithSnippetText: true,
+        includeCompletionsWithInsertText: true,
+    }
+});