fix(es/transforms/compat): Preserve more span (#2762)

swc_ecma_transforms_compat:
 - `async_to_generator`: Preserve more span. (Closes #2758)

crates/swc/tests/fixture/issue-2758/1/input/.swcrc

@@ -0,0 +1,5 @@
+{
+  "jsc": {
+    "target": "es2015"
+  }
+}

crates/swc/tests/fixture/issue-2758/1/input/index.js

@@ -0,0 +1,6 @@
+const obj = {
+  // A comment
+  async foo() {
+    console.log("Should work");
+  }
+}

crates/swc/tests/fixture/issue-2758/1/output/index.js

@@ -0,0 +1,37 @@
+function asyncGeneratorStep(gen, resolve, reject, _next, _throw, key, arg) {
+    try {
+        var info = gen[key](arg);
+        var value = info.value;
+    } catch (error) {
+        reject(error);
+        return;
+    }
+    if (info.done) {
+        resolve(value);
+    } else {
+        Promise.resolve(value).then(_next, _throw);
+    }
+}
+function _asyncToGenerator(fn) {
+    return function() {
+        var self = this, args = arguments;
+        return new Promise(function(resolve, reject) {
+            var gen = fn.apply(self, args);
+            function _next(value) {
+                asyncGeneratorStep(gen, resolve, reject, _next, _throw, "next", value);
+            }
+            function _throw(err) {
+                asyncGeneratorStep(gen, resolve, reject, _next, _throw, "throw", err);
+            }
+            _next(undefined);
+        });
+    };
+}
+const obj = {
+    // A comment
+    foo () {
+        return _asyncToGenerator(function*() {
+            console.log("Should work");
+        })();
+    }
+};

crates/swc_ecma_transforms_compat/src/es2017/async_to_generator.rs

@@ -395,6 +395,14 @@ impl VisitMut for Actual {
 
         let original_fn_params = prop.function.params.take();
 
+        let prop_method_span = prop.function.span;
+        let prop_method_body_span = if let Some(body) = &prop.function.body {
+            body.span
+        } else {
+            DUMMY_SP
+        };
+        prop.function.span = prop_method_body_span;
+
         let fn_ref = make_fn_ref(
             FnExpr {
                 ident: None,
@@ -423,7 +431,7 @@ impl VisitMut for Actual {
 
         prop.function = Function {
             params: original_fn_params,
-            span: DUMMY_SP,
+            span: prop_method_span,
             is_async: false,
             is_generator: false,
             body: Some(BlockStmt {

crates/swc_ecma_transforms_compat/src/es2020/export_namespace_from.rs

@@ -1,7 +1,7 @@
 use swc_common::DUMMY_SP;
 use swc_ecma_ast::*;
 use swc_ecma_utils::{IdentExt, IsDirective};
-use swc_ecma_visit::{as_folder, noop_fold_type, noop_visit_mut_type, Fold, VisitMut};
+use swc_ecma_visit::{as_folder, noop_visit_mut_type, Fold, VisitMut};
 
 pub fn export_namespace_from() -> impl Fold + VisitMut {
     as_folder(ExportNamespaceFrom)