fix(es/decorator): Support for legacy decorators in class expressions (…

…#8892)

**Related issue:**

- Closes #8515

crates/swc/tests/fixture/issues-8xxx/8095/es2020/output/1.js

@@ -1,10 +1,9 @@
 import { _ as _ts_decorate } from "@swc/helpers/_/_ts_decorate";
 var _class;
-const foo = _class = class _class {
+const foo = (_class = class _class {
     foo(v) {
         return v;
     }
-};
-_ts_decorate([
+}, _ts_decorate([
     foo
-], _class.prototype, "foo", null);
+], _class.prototype, "foo", null));

crates/swc/tests/fixture/issues-8xxx/8095/es2022/output/1.js

@@ -1,10 +1,9 @@
 import { _ as _ts_decorate } from "@swc/helpers/_/_ts_decorate";
 var _class;
-const foo = _class = class _class {
+const foo = (_class = class _class {
     foo(v) {
         return v;
     }
-};
-_ts_decorate([
+}, _ts_decorate([
     foo
-], _class.prototype, "foo", null);
+], _class.prototype, "foo", null));

crates/swc/tests/fixture/issues-8xxx/8095/es5/output/1.js

@@ -2,7 +2,7 @@ import { _ as _class_call_check } from "@swc/helpers/_/_class_call_check";
 import { _ as _create_class } from "@swc/helpers/_/_create_class";
 import { _ as _ts_decorate } from "@swc/helpers/_/_ts_decorate";
 var _class;
-var foo = _class = function() {
+var foo = (_class = function() {
     "use strict";
     function _class() {
         _class_call_check(this, _class);
@@ -16,7 +16,6 @@ var foo = _class = function() {
         }
     ]);
     return _class;
-}();
-_ts_decorate([
+}(), _ts_decorate([
     foo
-], _class.prototype, "foo", null);
+], _class.prototype, "foo", null));

crates/swc/tests/fixture/issues-8xxx/8515/input/.swcrc

@@ -0,0 +1,14 @@
+{
+    "jsc": {
+        "target": "es2016",
+        "keepClassNames": true,
+        "parser": {
+            "syntax": "ecmascript",
+            "decorators": true
+        },
+        "transform": {
+            "legacyDecorator": true,
+            "useDefineForClassFields": true
+        }
+    }
+}

crates/swc/tests/fixture/issues-8xxx/8515/input/index.js

@@ -0,0 +1,9 @@
+import { addX, addY } from 'someLib'
+
+var C = @addX @addY class extends Component {
+}
+
+@addX @addY
+class OtherClass extends Component {
+
+}

crates/swc/tests/fixture/issues-8xxx/8515/output/index.js

@@ -0,0 +1,14 @@
+import { _ as _ts_decorate } from "@swc/helpers/_/_ts_decorate";
+import { addX, addY } from 'someLib';
+var _class;
+var C = (_class = class _class extends Component {
+}, _class = _ts_decorate([
+    addX,
+    addY
+], _class));
+let OtherClass = class OtherClass extends Component {
+};
+OtherClass = _ts_decorate([
+    addX,
+    addY
+], OtherClass);

crates/swc_ecma_transforms_proposal/src/decorators/legacy/mod.rs

@@ -1,4 +1,4 @@
-use std::mem;
+use std::{iter, mem};
 
 use swc_atoms::JsWord;
 use swc_common::{collections::AHashMap, util::take::Take, DUMMY_SP};
@@ -268,7 +268,9 @@ impl VisitMut for TscDecorator {
     }
 
     fn visit_mut_expr(&mut self, e: &mut Expr) {
+        let appended_exprs = mem::take(&mut self.appended_exprs);
         e.visit_mut_children_with(self);
+        let appended_exprs = mem::replace(&mut self.appended_exprs, appended_exprs);
 
         if let Some(var_name) = self.assign_class_expr_to.take() {
             self.vars.push(VarDeclarator {
@@ -278,11 +280,17 @@ impl VisitMut for TscDecorator {
                 definite: Default::default(),
             });
 
-            *e = Expr::Assign(AssignExpr {
+            *e = Expr::Seq(SeqExpr {
                 span: DUMMY_SP,
-                op: op!("="),
-                left: var_name.into(),
-                right: Box::new(e.take()),
+                exprs: iter::once(AssignExpr {
+                    span: DUMMY_SP,
+                    op: op!("="),
+                    left: var_name.into(),
+                    right: Box::new(e.take()),
+                })
+                .map(Into::into)
+                .chain(appended_exprs)
+                .collect(),
             });
         }
     }