fix: provide caller information to Babel (#449)

* feat(babel): provide caller information to Babel

* Update test/transformers/babel.test.ts

* Skip providing `supportsExportNamespaceFrom: true` for now

* add comment for `supportsTopLevelAwait: true`

* chore: update src/transformers/babel.ts

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>
Co-authored-by: Christian Kaisermann <christian@kaisermann.me>

src/transformers/babel.ts

@@ -20,6 +20,17 @@ const transformer: Transformer<Options.Babel> = async ({
     minified: false,
     ast: false,
     code: true,
+    caller: {
+      name: 'svelte-preprocess',
+      supportsStaticESM: true,
+      supportsDynamicImport: true,
+      // this isn't supported by Svelte but let it error with a good error on this syntax untouched
+      supportsTopLevelAwait: true,
+      // todo: this can be enabled once all "peer deps" understand this
+      // this syntax is supported since rollup@1.26.0 and webpack@5.0.0-beta.21
+      // supportsExportNamespaceFrom: true,
+      ...options?.caller,
+    },
   } as TransformOptions;
 
   const result = await transformAsync(content, babelOptions);

test/transformers/babel.test.ts

@@ -40,4 +40,37 @@ $: bar = foo?.b ?? 120
       $: bar = (_foo$b = foo == null ? void 0 : foo.b) != null ? _foo$b : 120;</script>"
     `);
   });
+
+  it('should not transpile import/export syntax with preset-env', async () => {
+    const template = `<script>
+import foo from './foo'
+$: bar = foo?.b ?? 120
+</script>`;
+
+    const opts = sveltePreprocess({
+      babel: {
+        presets: [
+          [
+            '@babel/preset-env',
+            {
+              loose: true,
+              targets: {
+                esmodules: true,
+              },
+            },
+          ],
+        ],
+      },
+    });
+
+    const preprocessed = await preprocess(template, opts);
+
+    expect(preprocessed.code).toMatchInlineSnapshot(`
+      "<script>var _foo$b;
+
+      import foo from './foo';
+
+      $: bar = (_foo$b = foo == null ? void 0 : foo.b) != null ? _foo$b : 120;</script>"
+    `);
+  });
 });