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

Author: IAmArthurAdams

src/services/completions.ts

@@ -1860,7 +1860,38 @@ 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;