fix(isolated_declarations): Always emit module declarations that perform augmentation (#4919)

Fixes https://github.com/oxc-project/oxc/issues/4607

Co-authored-by: MichaelMitchell-at <=>

crates/oxc_isolated_declarations/src/lib.rs

@@ -325,6 +325,11 @@ impl<'a> IsolatedDeclarations<'a> {
                         new_ast_stmts.push(Statement::ImportDeclaration(decl));
                     }
                 }
+                Statement::TSModuleDeclaration(decl) => {
+                    if decl.kind.is_global() || decl.id.is_string_literal() {
+                        new_ast_stmts.push(Statement::TSModuleDeclaration(decl));
+                    }
+                }
                 _ => {}
             }
         }

crates/oxc_isolated_declarations/tests/fixtures/module-declaration.ts

@@ -0,0 +1,21 @@
+import 'foo';
+declare module 'foo' {
+    interface Foo {}
+    const foo = 42;
+}
+
+declare global {
+    interface Bar {}
+    const bar = 42 ;
+}
+
+// should not be emitted
+module baz {
+    interface Baz {}
+    const baz = 42;
+}
+
+declare module x {
+    interface Qux {}
+    const qux = 42;
+}

crates/oxc_isolated_declarations/tests/snapshots/module-declaration.snap

@@ -0,0 +1,15 @@
+---
+source: crates/oxc_isolated_declarations/tests/mod.rs
+input_file: crates/oxc_isolated_declarations/tests/fixtures/module-declaration.ts
+---
+==================== .D.TS ====================
+
+import "foo";
+declare module "foo" {
+	interface Foo {}
+	const foo = 42;
+}
+declare global {
+	interface Bar {}
+	const bar = 42;
+}