fix(isolated_declarations): namespaces that are default exported should be considered for expando functions (#4935)

This should be ok but currently has an error reported
```ts
function foo(): void {}

namespace foo {
  export let bar = 42;
}

foo.bar = 42;

export default foo;
```

Co-authored-by: MichaelMitchell-at <=>
Co-authored-by: Dunqing <dengqing0821@gmail.com>
Co-authored-by: Don Isaac <donald.isaac@gmail.com>

crates/oxc_isolated_declarations/src/lib.rs

@@ -425,8 +425,18 @@ impl<'a> IsolatedDeclarations<'a> {
     ) -> FxHashMap<&'a str, FxHashSet<Atom>> {
         let mut assignable_properties_for_namespace = FxHashMap::<&str, FxHashSet<Atom>>::default();
         for stmt in stmts {
-            let Statement::ExportNamedDeclaration(decl) = stmt else { continue };
+            let decl = match stmt {
-            let Some(Declaration::TSModuleDeclaration(decl)) = &decl.declaration else { continue };
+                Statement::ExportNamedDeclaration(decl) => {
+                    if let Some(Declaration::TSModuleDeclaration(decl)) = &decl.declaration {
+                        decl
+                    } else {
+                        continue;
+                    }
+                }
+                Statement::TSModuleDeclaration(decl) => decl,
+                _ => continue,
+            };
+
             if decl.kind != TSModuleDeclarationKind::Namespace {
                 continue;
             }

crates/oxc_isolated_declarations/tests/fixtures/expando-function.ts

@@ -16,14 +16,19 @@ export namespace foo {
   export let baz = 100;
 }
 
-// namespace must be exported
-namespace foo {
-  export let bar = 42;
-}
-
 foo.bar = 42;
 foo.baz = 100;
 
 // unexported
 const zoo = (): void => {}
 zoo.toString = () => {}
+
+function qux(): void {}
+
+namespace qux {
+  export let woo = 42;
+}
+
+qux.woo = 42;
+
+export default qux;

crates/oxc_isolated_declarations/tests/snapshots/expando-function.snap

@@ -12,6 +12,11 @@ export declare namespace NS {
 export declare namespace foo {
 	export let baz: number;
 }
+declare function qux(): void;
+declare namespace qux {
+	export let woo: number;
+}
+export default qux;
 
 
 ==================== Errors ====================
@@ -49,9 +54,9 @@ export declare namespace foo {
   x TS9023: Assigning properties to functions without declaring them is not
   | supported with --isolatedDeclarations. Add an explicit declaration for the
   | properties assigned to this function.
-    ,-[24:1]
+    ,-[19:1]
- 23 | 
+ 18 | 
- 24 | foo.bar = 42;
+ 19 | foo.bar = 42;
     : ^^^^^^^
- 25 | foo.baz = 100;
+ 20 | foo.baz = 100;
     `----