Fix widened type in declarations files.

Author: dragomirtitian

src/compiler/checker.ts

@@ -48324,8 +48324,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         // Get type of the symbol if this is the valid symbol otherwise get type at location
         const symbol = getSymbolOfDeclaration(declaration);
         let type = symbol && !(symbol.flags & (SymbolFlags.TypeLiteral | SymbolFlags.Signature))
-            ? getWidenedLiteralType(getTypeOfSymbol(symbol))
+            ? getTypeOfSymbol(symbol)
             : errorType;
+        if (!isReadonlySymbol(symbol)) {
+            type = getWidenedLiteralType(type);
+        }
         if (
             type.flags & TypeFlags.UniqueESSymbol &&
             type.symbol === symbol

tests/baselines/reference/ambientConstLiterals.js

@@ -74,5 +74,5 @@ declare const c9: {
 declare const c10: number[];
 declare const c11: string;
 declare const c12: number;
-declare const c13: string;
-declare const c14: number;
+declare const c13: "abc" | "def";
+declare const c14: 123 | 456;

tests/baselines/reference/strictFunctionTypes1.js

@@ -82,7 +82,7 @@ declare function fs(x: string): void;
 declare function fx(f: (x: "def") => void): void;
 declare const x1: (x: string) => void;
 declare const x2 = "abc";
-declare const x3: string;
+declare const x3: "def" | "abc";
 declare const x4: Func<string>;
 declare const never: never;
 declare const x10: string;

tests/baselines/reference/stringLiteralTypesOverloads02.js

@@ -104,9 +104,9 @@ declare namespace Consts1 {
 declare const string = "string";
 declare const number = "number";
 declare const boolean = "boolean";
-declare const stringOrNumber: string;
-declare const stringOrBoolean: string;
-declare const booleanOrNumber: string;
-declare const stringOrBooleanOrNumber: string;
+declare const stringOrNumber: "string" | "number";
+declare const stringOrBoolean: "string" | "boolean";
+declare const booleanOrNumber: "number" | "boolean";
+declare const stringOrBooleanOrNumber: "string" | "number" | "boolean";
 declare namespace Consts2 {
 }

tests/baselines/reference/verbatim-declarations-literals.js

@@ -60,7 +60,7 @@ declare enum E {
 }
 declare const e = E["some value"];
 declare function f3<T>(a: T, b: T): T;
-declare const x3: string;
+declare const x3: "abc" | "def";
 declare const octal = 14;
 declare const octalParen = 14;
 declare const octalIndirect = 14;