Fixed quick info display for aliased symbols in type-narrowed locations (#54763)

Author: Andarist

src/services/symbolDisplay.ts

@@ -254,18 +254,15 @@ export interface SymbolDisplayPartsDocumentationAndSymbolKind {
     tags: JSDocTagInfo[] | undefined;
 }
 
-// TODO(drosen): Currently completion entry details passes the SemanticMeaning.All instead of using semanticMeaning of location
-/** @internal */
-export function getSymbolDisplayPartsDocumentationAndSymbolKind(typeChecker: TypeChecker, symbol: Symbol, sourceFile: SourceFile, enclosingDeclaration: Node | undefined,
-    location: Node, semanticMeaning = getMeaningFromLocation(location), alias?: Symbol): SymbolDisplayPartsDocumentationAndSymbolKind {
+function getSymbolDisplayPartsDocumentationAndSymbolKindWorker(typeChecker: TypeChecker, symbol: Symbol, sourceFile: SourceFile, enclosingDeclaration: Node | undefined,
+    location: Node, type: Type | undefined, semanticMeaning: SemanticMeaning, alias?: Symbol): SymbolDisplayPartsDocumentationAndSymbolKind {
     const displayParts: SymbolDisplayPart[] = [];
     let documentation: SymbolDisplayPart[] = [];
     let tags: JSDocTagInfo[] = [];
     const symbolFlags = getCombinedLocalAndExportSymbolFlags(symbol);
     let symbolKind = semanticMeaning & SemanticMeaning.Value ? getSymbolKindOfConstructorPropertyMethodAccessorFunctionOrVar(typeChecker, symbol, location) : ScriptElementKind.unknown;
     let hasAddedSymbolInfo = false;
     const isThisExpression = location.kind === SyntaxKind.ThisKeyword && isInExpressionContext(location) || isThisInTypeQuery(location);
-    let type: Type | undefined;
     let documentationFromAlias: SymbolDisplayPart[] | undefined;
     let tagsFromAlias: JSDocTagInfo[] | undefined;
     let hasMultipleSignatures = false;
@@ -300,7 +297,7 @@ export function getSymbolDisplayPartsDocumentationAndSymbolKind(typeChecker: Typ
         }
 
         let signature: Signature | undefined;
-        type = isThisExpression ? typeChecker.getTypeAtLocation(location) : typeChecker.getTypeOfSymbolAtLocation(symbol, location);
+        type ??= isThisExpression ? typeChecker.getTypeAtLocation(location) : typeChecker.getTypeOfSymbolAtLocation(symbol, location);
 
         if (location.parent && location.parent.kind === SyntaxKind.PropertyAccessExpression) {
             const right = (location.parent as PropertyAccessExpression).name;
@@ -553,12 +550,13 @@ export function getSymbolDisplayPartsDocumentationAndSymbolKind(typeChecker: Typ
                         isModuleWithStringLiteralName(resolvedNode) &&
                         hasSyntacticModifier(resolvedNode, ModifierFlags.Ambient);
                     const shouldUseAliasName = symbol.name !== "default" && !isExternalModuleDeclaration;
-                    const resolvedInfo = getSymbolDisplayPartsDocumentationAndSymbolKind(
+                    const resolvedInfo = getSymbolDisplayPartsDocumentationAndSymbolKindWorker(
                         typeChecker,
                         resolvedSymbol,
                         getSourceFileOfNode(resolvedNode),
                         resolvedNode,
                         declarationName,
+                        type,
                         semanticMeaning,
                         shouldUseAliasName ? symbol : resolvedSymbol);
                     displayParts.push(...resolvedInfo.displayParts);
@@ -858,6 +856,13 @@ export function getSymbolDisplayPartsDocumentationAndSymbolKind(typeChecker: Typ
     }
 }
 
+// TODO(drosen): Currently completion entry details passes the SemanticMeaning.All instead of using semanticMeaning of location
+/** @internal */
+export function getSymbolDisplayPartsDocumentationAndSymbolKind(typeChecker: TypeChecker, symbol: Symbol, sourceFile: SourceFile, enclosingDeclaration: Node | undefined,
+    location: Node, semanticMeaning = getMeaningFromLocation(location), alias?: Symbol): SymbolDisplayPartsDocumentationAndSymbolKind {
+    return getSymbolDisplayPartsDocumentationAndSymbolKindWorker(typeChecker, symbol, sourceFile, enclosingDeclaration, location, /*type*/ undefined, semanticMeaning, alias);
+}
+
 function isLocalVariableOrFunction(symbol: Symbol) {
     if (symbol.parent) {
         return false; // This is exported symbol

tests/cases/fourslash/quickInfoNarrowedTypeOfAliasSymbol.ts

@@ -0,0 +1,17 @@
+/// <reference path='fourslash.ts' />
+// @strict: true
+
+// @Filename: modules.ts
+//// export declare const someEnv: string | undefined;
+
+// @Filename: app.ts
+//// import { someEnv } from "./modules";
+//// declare function isString(v: any): v is string;
+////
+//// if (isString(someEnv)) {
+////   someEnv/*1*/.charAt(0);
+//// }
+
+goTo.file("app.ts");
+goTo.marker("1");
+verify.quickInfoIs(`(alias) const someEnv: string\nimport someEnv`);