Fix export default dts widening

internal/checker/nodebuilderimpl.go

@@ -2181,7 +2181,15 @@ func (b *NodeBuilderImpl) serializeTypeForDeclaration(declaration *ast.Declarati
 			if symbol.Flags&ast.SymbolFlagsAccessor != 0 && declaration.Kind == ast.KindSetAccessor {
 				t = b.ch.instantiateType(b.ch.getWriteTypeOfSymbol(symbol), b.ctx.mapper)
 			} else if symbol != nil && (symbol.Flags&(ast.SymbolFlagsTypeLiteral|ast.SymbolFlagsSignature) == 0) {
-				t = b.ch.instantiateType(b.ch.getWidenedLiteralType(b.ch.getTypeOfSymbol(symbol)), b.ctx.mapper)
+				symType := b.ch.getTypeOfSymbol(symbol)
+				// Don't widen literals for export assignments — the emitted declaration is
+				// `const _default: <type>`, and a const should preserve the literal type.
+				// Strada handles this via preserveLiterals in the syntactic type builder;
+				// we handle it by not widening the checker type in the first place.
+				if !ast.IsAnyExportAssignment(declaration) {
+					symType = b.ch.getWidenedLiteralType(symType)
+				}
+				t = b.ch.instantiateType(symType, b.ctx.mapper)
 			} else {
 				t = b.ch.errorType
 			}

internal/checker/pseudotypenodebuilder.go

@@ -623,7 +623,7 @@ func (b *NodeBuilderImpl) pseudoTypeToType(t *pseudochecker.PseudoType) *Type {
 		return b.ch.trueType
 	case pseudochecker.PseudoTypeKindStringLiteral, pseudochecker.PseudoTypeKindNumericLiteral, pseudochecker.PseudoTypeKindBigIntLiteral:
 		source := t.AsPseudoTypeLiteral().Node
-		return b.ch.getWidenedType(b.ch.getRegularTypeOfExpression(source)) // big shortcut, uses cached expression types where possible
+		return b.ch.getRegularTypeOfExpression(source) // big shortcut, uses cached expression types where possible
 	case pseudochecker.PseudoTypeKindObjectLiteral, pseudochecker.PseudoTypeKindSingleCallSignature, pseudochecker.PseudoTypeKindTuple:
 		return nil // no simple mapping to a type, since these are structural types
 	default:

internal/execute/tsctests/tsc_test.go

@@ -1584,7 +1584,6 @@ func TestTscIncremental(t *testing.T) {
 					edit: func(sys *TestSys) {
 						sys.writeFileNoError("/home/src/workspaces/project/constants.ts", "export default 2;")
 					},
-					expectedDiff: "Currently there is issue with d.ts emit for export default = 1 to widen in dts which is why we are not re-computing errors and results in incorrect error reporting",
 				},
 			},
 		},
@@ -1610,7 +1609,6 @@ func TestTscIncremental(t *testing.T) {
 					edit: func(sys *TestSys) {
 						sys.writeFileNoError("/home/src/workspaces/project/constants.ts", "export default 2;")
 					},
-					expectedDiff: "Currently there is issue with d.ts emit for export default = 1 to widen in dts which is why we are not re-computing errors and results in incorrect error reporting",
 				},
 			},
 		},

testdata/baselines/reference/compiler/jsdocCommentDefaultExport(module=commonjs).js

@@ -78,7 +78,7 @@ export default class {
 }
 //// [exportDefaultLiteral.d.ts]
 /** Literal comment */
-declare const _default: number;
+declare const _default: 42;
 export default _default;
 //// [exportDefaultNull.d.ts]
 /** Null comment */

testdata/baselines/reference/compiler/jsdocCommentDefaultExport(module=esnext).js

@@ -66,7 +66,7 @@ export default class {
 }
 //// [exportDefaultLiteral.d.ts]
 /** Literal comment */
-declare const _default: number;
+declare const _default: 42;
 export default _default;
 //// [exportDefaultNull.d.ts]
 /** Null comment */

testdata/baselines/reference/submodule/compiler/dynamicImportsDeclaration.js

@@ -52,13 +52,13 @@ exports.mod = await (async () => {
 
 
 //// [case0.d.ts]
-declare const _default: number;
+declare const _default: 0;
 export default _default;
 //// [case1.d.ts]
-declare const _default: number;
+declare const _default: 1;
 export default _default;
 //// [caseFallback.d.ts]
-declare const _default: string;
+declare const _default: "fallback";
 export default _default;
 //// [index.d.ts]
 export declare const mod: {

testdata/baselines/reference/submodule/compiler/modulePreserve4.js

@@ -197,7 +197,7 @@ export {}; // Silly test harness
 //// [a.d.ts]
 export declare const x = 0;
 //// [b.d.ts]
-declare const _default: number;
+declare const _default: 0;
 export default _default;
 //// [c.d.ts]
 declare const _default: {
@@ -208,10 +208,10 @@ export = _default;
 declare const _default: () => void;
 export = _default;
 //// [e.d.mts]
-declare const _default: number;
+declare const _default: 0;
 export = _default;
 //// [f.d.cts]
-declare const _default: number;
+declare const _default: 0;
 export default _default;
 //// [g.d.ts]
 declare const _default: 0;

testdata/baselines/reference/submodule/compiler/modulePreserve4.js.diff

@@ -7,25 +7,9 @@
 -export const x: 0;
 +export declare const x = 0;
  //// [b.d.ts]
--declare const _default: 0;
-+declare const _default: number;
- export default _default;
- //// [c.d.ts]
- declare const _default: {
-@@= skipped -13, +13 lines =@@
- declare const _default: () => void;
- export = _default;
- //// [e.d.mts]
--declare const _default: 0;
-+declare const _default: number;
- export = _default;
- //// [f.d.cts]
--declare const _default: 0;
-+declare const _default: number;
- export default _default;
- //// [g.d.ts]
  declare const _default: 0;
-@@= skipped -15, +15 lines =@@
+ export default _default;
+@@= skipped -28, +28 lines =@@
  //// [main3.d.cts]
  export {};
  //// [main4.d.cts]

testdata/baselines/reference/submodule/compiler/nodeNextCjsNamespaceImportDefault2.js

@@ -27,7 +27,7 @@ ns.default.a;
 
 //// [a.d.cts]
 export declare const a: number;
-declare const _default: string;
+declare const _default: "string";
 export default _default;
 //// [foo.d.mts]
 import d, { a } from './a.cjs';

testdata/baselines/reference/submodule/conformance/jsDeclarationsDefault(target=es2015).js

@@ -101,7 +101,7 @@ function func() { }
 
 
 //// [index1.d.ts]
-declare const _default: number;
+declare const _default: 12;
 export default _default;
 //// [index2.d.ts]
 export default function foo(): typeof foo;
@@ -120,7 +120,7 @@ declare class Bar extends Fab {
 }
 export default Bar;
 //// [index5.d.ts]
-declare const _default: number;
+declare const _default: 12;
 export default _default;
 export type default = string | number;
 /**

testdata/baselines/reference/submodule/conformance/jsDeclarationsDefault(target=es2015).js.diff

@@ -1,11 +1,6 @@
 --- old.jsDeclarationsDefault(target=es2015).js
 +++ new.jsDeclarationsDefault(target=es2015).js
-@@= skipped -100, +100 lines =@@
-
-
- //// [index1.d.ts]
--declare const _default: 12;
-+declare const _default: number;
+@@= skipped -104, +104 lines =@@
  export default _default;
  //// [index2.d.ts]
  export default function foo(): typeof foo;
@@ -29,8 +24,7 @@
 +export default Bar;
  //// [index5.d.ts]
 -type _default = string | number;
--declare const _default: 12;
-+declare const _default: number;
+ declare const _default: 12;
  export default _default;
 +export type default = string | number;
 +/**

testdata/baselines/reference/tsc/composite/synthetic-jsx-import-of-ESM-module-from-CJS-module-no-crash-no-jsx-element.js

@@ -26,7 +26,7 @@ tsgo
 ExitStatus:: Success
 Output::
 //// [/home/src/projects/project/src/main.d.ts] *new* 
-declare const _default: number;
+declare const _default: 42;
 export default _default;
 
 //// [/home/src/projects/project/src/main.js] *new* 
@@ -35,7 +35,7 @@ Object.defineProperty(exports, "__esModule", { value: true });
 exports.default = 42;
 
 //// [/home/src/projects/project/tsconfig.tsbuildinfo] *new* 
-{"version":"FakeTSVersion","root":[3],"fileNames":["lib.es2025.full.d.ts","./node_modules/solid-js/jsx-runtime.d.ts","./src/main.ts"],"fileInfos":[{"version":"8859c12c614ce56ba9a18e58384a198f-/// <reference no-default-lib=\"true\"/>\ninterface Boolean {}\ninterface Function {}\ninterface CallableFunction {}\ninterface NewableFunction {}\ninterface IArguments {}\ninterface Number { toExponential: any; }\ninterface Object {}\ninterface RegExp {}\ninterface String { charAt: any; }\ninterface Array<T> { length: number; [n: number]: T; }\ninterface ReadonlyArray<T> {}\ninterface SymbolConstructor {\n    (desc?: string | number): symbol;\n    for(name: string): symbol;\n    readonly toStringTag: symbol;\n}\ndeclare var Symbol: SymbolConstructor;\ninterface Symbol {\n    readonly [Symbol.toStringTag]: string;\n}\ndeclare const console: { log(msg: any): void; };","affectsGlobalScope":true,"impliedNodeFormat":1},{"version":"00e459cbb1596f8c4bdf988b0589433f-export namespace JSX {\n    type IntrinsicElements = { div: {}; };\n}","impliedNodeFormat":99},{"version":"666fdc0c7a7f134c8c14dc85be1ebc28-export default 42;","signature":"18ae69a2c0b372747b9973ad9c14a1e0-declare const _default: number;\nexport default _default;\n","impliedNodeFormat":1}],"options":{"composite":true,"jsx":4,"jsxImportSource":"solid-js","module":100},"latestChangedDtsFile":"./src/main.d.ts"}
+{"version":"FakeTSVersion","root":[3],"fileNames":["lib.es2025.full.d.ts","./node_modules/solid-js/jsx-runtime.d.ts","./src/main.ts"],"fileInfos":[{"version":"8859c12c614ce56ba9a18e58384a198f-/// <reference no-default-lib=\"true\"/>\ninterface Boolean {}\ninterface Function {}\ninterface CallableFunction {}\ninterface NewableFunction {}\ninterface IArguments {}\ninterface Number { toExponential: any; }\ninterface Object {}\ninterface RegExp {}\ninterface String { charAt: any; }\ninterface Array<T> { length: number; [n: number]: T; }\ninterface ReadonlyArray<T> {}\ninterface SymbolConstructor {\n    (desc?: string | number): symbol;\n    for(name: string): symbol;\n    readonly toStringTag: symbol;\n}\ndeclare var Symbol: SymbolConstructor;\ninterface Symbol {\n    readonly [Symbol.toStringTag]: string;\n}\ndeclare const console: { log(msg: any): void; };","affectsGlobalScope":true,"impliedNodeFormat":1},{"version":"00e459cbb1596f8c4bdf988b0589433f-export namespace JSX {\n    type IntrinsicElements = { div: {}; };\n}","impliedNodeFormat":99},{"version":"666fdc0c7a7f134c8c14dc85be1ebc28-export default 42;","signature":"e48ca0859b14891cbeb31bf4dec89530-declare const _default: 42;\nexport default _default;\n","impliedNodeFormat":1}],"options":{"composite":true,"jsx":4,"jsxImportSource":"solid-js","module":100},"latestChangedDtsFile":"./src/main.d.ts"}
 //// [/home/src/projects/project/tsconfig.tsbuildinfo.readable.baseline.txt] *new* 
 {
   "version": "FakeTSVersion",
@@ -78,11 +78,11 @@ exports.default = 42;
     {
       "fileName": "./src/main.ts",
       "version": "666fdc0c7a7f134c8c14dc85be1ebc28-export default 42;",
-      "signature": "18ae69a2c0b372747b9973ad9c14a1e0-declare const _default: number;\nexport default _default;\n",
+      "signature": "e48ca0859b14891cbeb31bf4dec89530-declare const _default: 42;\nexport default _default;\n",
       "impliedNodeFormat": "CommonJS",
       "original": {
         "version": "666fdc0c7a7f134c8c14dc85be1ebc28-export default 42;",
-        "signature": "18ae69a2c0b372747b9973ad9c14a1e0-declare const _default: number;\nexport default _default;\n",
+        "signature": "e48ca0859b14891cbeb31bf4dec89530-declare const _default: 42;\nexport default _default;\n",
         "impliedNodeFormat": 1
       }
     }
@@ -94,7 +94,7 @@ exports.default = 42;
     "module": 100
   },
   "latestChangedDtsFile": "./src/main.d.ts",
-  "size": 1373
+  "size": 1369
 }
 //// [/home/src/tslibs/TS/Lib/lib.es2025.full.d.ts] *Lib*
 /// <reference no-default-lib="true"/>