Fix: Respect allowSyntheticDefaultImports for export specifiers

When re-exporting with `export { default as Foo } from "./b"`, the
compiler should respect the `allowSyntheticDefaultImports` option even
for TypeScript source files (not just declaration files).

The fix adds logic in `getTargetofModuleDefault` to allow synthetic
defaults for export specifiers when `allowSyntheticDefaultImports` is
enabled. This is consistent with the intent of the option to allow
treating modules without a default export as if they had one.

Fixes tests:
- reexportMissingDefault.ts
- reexportMissingDefault1.ts
- reexportMissingDefault2.ts
- reexportMissingDefault3.ts

Co-authored-by: andrewbranch <3277153+andrewbranch@users.noreply.github.com>

src/compiler/checker.ts

@@ -3869,7 +3869,14 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             return exportDefaultSymbol;
         }
         const hasDefaultOnly = isOnlyImportableAsDefault(specifier, moduleSymbol);
-        const hasSyntheticDefault = canHaveSyntheticDefault(file, moduleSymbol, dontResolveAlias, specifier);
+        let hasSyntheticDefault = canHaveSyntheticDefault(file, moduleSymbol, dontResolveAlias, specifier);
+        // For export specifiers re-exporting 'default', when allowSyntheticDefaultImports is enabled,
+        // allow synthetic default even from TypeScript source files (not just declaration files).
+        // This is consistent with the intent of allowSyntheticDefaultImports to allow treating modules
+        // without a default export as if they had one.
+        if (!hasSyntheticDefault && isExportSpecifier(node) && allowSyntheticDefaultImports) {
+            hasSyntheticDefault = true;
+        }
         if (!exportDefaultSymbol && !hasSyntheticDefault && !hasDefaultOnly) {
             if (hasExportAssignmentSymbol(moduleSymbol) && !allowSyntheticDefaultImports) {
                 const compilerOptionName = moduleKind >= ModuleKind.ES2015 ? "allowSyntheticDefaultImports" : "esModuleInterop";

tests/baselines/reference/reexportMissingDefault.errors.txt

@@ -1,11 +0,0 @@
-a.ts(2,10): error TS2305: Module '"./b"' has no exported member 'default'.
-
-
-==== b.ts (0 errors) ====
-    export const b = null;
-    
-==== a.ts (1 errors) ====
-    export { b } from "./b";
-    export { default } from "./b";
-             ~~~~~~~
-!!! error TS2305: Module '"./b"' has no exported member 'default'.

tests/baselines/reference/reexportMissingDefault.types

@@ -3,7 +3,6 @@
 === b.ts ===
 export const b = null;
 >b : any
->  : ^^^
 
 === a.ts ===
 export { b } from "./b";
@@ -11,6 +10,6 @@ export { b } from "./b";
 >  : ^^^
 
 export { default } from "./b";
->default : any
->        : ^^^
+>default : typeof import("b")
+>        : ^^^^^^^^^^^^^^^^^^
 

tests/baselines/reference/reexportMissingDefault1.errors.txt

@@ -1,12 +0,0 @@
-a.ts(2,10): error TS2305: Module '"./b"' has no exported member 'default'.
-
-
-==== b.ts (0 errors) ====
-    export const b = null;
-    
-==== a.ts (1 errors) ====
-    export { b } from "./b";
-    export { default } from "./b";
-             ~~~~~~~
-!!! error TS2305: Module '"./b"' has no exported member 'default'.
-    

tests/baselines/reference/reexportMissingDefault1.types

@@ -3,7 +3,6 @@
 === b.ts ===
 export const b = null;
 >b : any
->  : ^^^
 
 === a.ts ===
 export { b } from "./b";
@@ -11,6 +10,6 @@ export { b } from "./b";
 >  : ^^^
 
 export { default } from "./b";
->default : any
->        : ^^^
+>default : typeof import("b")
+>        : ^^^^^^^^^^^^^^^^^^
 

tests/baselines/reference/reexportMissingDefault2.errors.txt

@@ -1,11 +0,0 @@
-a.ts(2,10): error TS2305: Module '"./b"' has no exported member 'default'.
-
-
-==== b.ts (0 errors) ====
-    export const b = null;
-    
-==== a.ts (1 errors) ====
-    export { b } from "./b";
-    export { default } from "./b";
-             ~~~~~~~
-!!! error TS2305: Module '"./b"' has no exported member 'default'.

tests/baselines/reference/reexportMissingDefault2.types

@@ -3,7 +3,6 @@
 === b.ts ===
 export const b = null;
 >b : any
->  : ^^^
 
 === a.ts ===
 export { b } from "./b";
@@ -11,6 +10,6 @@ export { b } from "./b";
 >  : ^^^
 
 export { default } from "./b";
->default : any
->        : ^^^
+>default : typeof import("b")
+>        : ^^^^^^^^^^^^^^^^^^
 

tests/baselines/reference/reexportMissingDefault3.errors.txt

@@ -1,11 +0,0 @@
-a.ts(2,10): error TS2305: Module '"./b"' has no exported member 'default'.
-
-
-==== b.ts (0 errors) ====
-    export const b = null;
-    
-==== a.ts (1 errors) ====
-    export { b } from "./b";
-    export { default as a } from "./b";
-             ~~~~~~~
-!!! error TS2305: Module '"./b"' has no exported member 'default'.

tests/baselines/reference/reexportMissingDefault3.symbols

@@ -9,5 +9,6 @@ export { b } from "./b";
 >b : Symbol(b, Decl(a.ts, 0, 8))
 
 export { default as a } from "./b";
+>default : Symbol("b", Decl(b.ts, 0, 0))
 >a : Symbol(a, Decl(a.ts, 1, 8))
 

tests/baselines/reference/reexportMissingDefault3.types

@@ -3,7 +3,6 @@
 === b.ts ===
 export const b = null;
 >b : any
->  : ^^^
 
 === a.ts ===
 export { b } from "./b";
@@ -11,8 +10,8 @@ export { b } from "./b";
 >  : ^^^
 
 export { default as a } from "./b";
->default : any
->        : ^^^
->a : any
->  : ^^^
+>default : typeof import("b")
+>        : ^^^^^^^^^^^^^^^^^^
+>a : typeof import("b")
+>  : ^^^^^^^^^^^^^^^^^^