fix: TS declare class in namespace should be removed

packages/babel-plugin-transform-typescript/src/namespace.ts

@@ -81,11 +81,14 @@ function handleVariableDeclaration(
     // `export const a = 1` transforms to `const a = N.a = 1`, the output
     // is smaller than `const a = 1; N.a = a`;
     for (const declarator of declarations) {
-      declarator.init = t.assignmentExpression(
-        "=",
-        getMemberExpression(name, declarator.id.name),
-        declarator.init,
-      );
+      // `export declare const a`,the declarator.init would be null,
+      if (declarator.init) {
+        declarator.init = t.assignmentExpression(
+          "=",
+          getMemberExpression(name, declarator.id.name),
+          declarator.init,
+        );
+      }
     }
     return [node];
   }
@@ -185,6 +188,10 @@ function handleNested(
       case "TSEnumDeclaration":
       case "FunctionDeclaration":
       case "ClassDeclaration": {
+        if (subNode.declaration.declare) {
+          continue;
+        }
+
         const itemName = subNode.declaration.id.name;
         names.add(itemName);
         namespaceTopLevel.splice(

packages/babel-plugin-transform-typescript/test/fixtures/namespace/declare/input.ts

@@ -0,0 +1,7 @@
+export namespace N {
+  export declare class C {
+  }
+  export declare enum e { };
+  export declare function f(): void;
+  export declare const v: unknown;
+}

packages/babel-plugin-transform-typescript/test/fixtures/namespace/declare/output.mjs

@@ -0,0 +1,5 @@
+export let N;
+
+(function (_N) {
+  ;
+})(N || (N = {}));