fix: don't use the globalThis shim when there are no shimmed globals (#517)

Author: dsherret

rs-lib/src/visitors/globals.rs

@@ -87,13 +87,16 @@ fn visit_children(node: Node, import_name: &str, context: &mut Context) {
     let ident_text = ident.text_fast(context.program);
 
     if is_unresolved_context {
-      // check to replace globalThis
+      // check to replace globalThis, which is only necessary when there
+      // are globals to merge into it
       if ident_text == "globalThis" {
-        if let Some(text_change) =
-          get_global_this_text_change(ident, import_name, context)
-        {
-          context.text_changes.push(text_change);
-          context.import_shim = true;
+        if !context.shim_global_names.is_empty() {
+          if let Some(text_change) =
+            get_global_this_text_change(ident, import_name, context)
+          {
+            context.text_changes.push(text_change);
+            context.import_shim = true;
+          }
         }
         return;
       }

rs-lib/tests/integration_test.rs

@@ -461,6 +461,28 @@ async fn transform_global_this_shim() {
   .await;
 }
 
+#[tokio::test]
+async fn no_transform_global_this_when_no_shims() {
+  // there's nothing to merge into `globalThis`, so it should be left
+  // alone and no shim file should be created
+  let text = concat!(
+    "globalThis.Deno.readTextFile();",
+    "true ? globalThis : globalThis;",
+    "typeof globalThis;",
+    "globalThis == null;",
+    "type Test = typeof globalThis;",
+  );
+  let result = TestBuilder::new()
+    .with_loader(|loader| {
+      loader.add_local_file("/mod.ts", text);
+    })
+    .transform()
+    .await
+    .unwrap();
+
+  assert_files!(result.main.files, &[("mod.ts", text)]);
+}
+
 #[tokio::test]
 async fn no_transform_window() {
   // `window` is not a global in Node.js nor Deno, so leave it alone