fix: duplicate CommonJS exports

Author: marvinhagemeister

packages/plugin-vite/src/plugins/commonjs.ts

@@ -33,6 +33,28 @@ export function cjsPlugin(
 
           if (body.length === 0 && state.get(HAS_ES_MODULE)) {
             path.pushContainer("body", t.exportNamedDeclaration(null));
+          } else {
+            const seen = new Set<string>();
+
+            const children = path.get("body");
+            for (let i = children.length - 1; i >= 0; i--) {
+              const child = children[i];
+              if (child.isExportNamedDeclaration()) {
+                if (
+                  t.isVariableDeclaration(child.node.declaration) &&
+                  child.node.declaration.declarations.length > 0 &&
+                  t.isIdentifier(child.node.declaration.declarations[0].id)
+                ) {
+                  const name = child.node.declaration.declarations[0].id.name;
+
+                  if (seen.has(name)) {
+                    child.remove();
+                  } else {
+                    seen.add(name);
+                  }
+                }
+              }
+            }
           }
         },
       },

packages/plugin-vite/src/plugins/commonjs_test.ts

@@ -165,6 +165,15 @@ var a = _mod.default ?? _mod,
   });
 });
 
+Deno.test("commonjs - duplicate exports", () => {
+  runTest({
+    input: `Object.defineProperty(exports, "__esModule", { value: true });
+exports.trace = void 0;
+exports.trace = 'foo'`,
+    expected: `export let trace = 'foo';`,
+  });
+});
+
 // I've never seen this, seems rare. Skipping for now.
 Deno.test.ignore("commonjs - require", () => {
   runTest({