fix(es/module): Fix handling of this for systemjs (#6857)

**Related issue:**

 - Closes #6784.

Author: vasilev-alex

crates/swc/tests/tsc-references/classStaticBlock24(module=system).1.normal.js

@@ -13,7 +13,7 @@ System.register([
         execute: function() {
             _export("C", C = function C() {
                 "use strict";
-                _class_call_check(void 0, C);
+                _class_call_check(this, C);
             });
             __ = {
                 writable: true,

crates/swc/tests/tsc-references/classStaticBlock24(module=system).2.minified.js

@@ -13,7 +13,7 @@ System.register([
         execute: function() {
             _export("C", C = function C() {
                 "use strict";
-                _class_call_check(void 0, C);
+                _class_call_check(this, C);
             }), C.x = 1;
         }
     };

crates/swc/tests/tsc-references/exportClassNameWithObjectSystem.1.normal.js

@@ -13,7 +13,7 @@ System.register([
         execute: function() {
             _export("Object", Object = function Object() {
                 "use strict";
-                _class_call_check(void 0, Object);
+                _class_call_check(this, Object);
             });
         }
     };

crates/swc/tests/tsc-references/exportClassNameWithObjectSystem.2.minified.js

@@ -13,7 +13,7 @@ System.register([
         execute: function() {
             _export("Object", function Object() {
                 "use strict";
-                _class_call_check(void 0, Object);
+                _class_call_check(this, Object);
             });
         }
     };

crates/swc/tests/tsc-references/importCallExpressionAsyncES3System.1.normal.js

@@ -91,8 +91,8 @@ System.register([
             });
             _export("cl2", cl2 = function cl2() {
                 "use strict";
-                _class_call_check(void 0, cl2);
-                (void 0).p = {
+                _class_call_check(this, cl2);
+                this.p = {
                     m: /*#__PURE__*/ _async_to_generator(function() {
                         var req;
                         return _ts_generator(this, function(_state) {

crates/swc/tests/tsc-references/importCallExpressionAsyncES5System.1.normal.js

@@ -91,8 +91,8 @@ System.register([
             });
             _export("cl2", cl2 = function cl2() {
                 "use strict";
-                _class_call_check(void 0, cl2);
-                (void 0).p = {
+                _class_call_check(this, cl2);
+                this.p = {
                     m: /*#__PURE__*/ _async_to_generator(function() {
                         var req;
                         return _ts_generator(this, function(_state) {

crates/swc/tests/tsc-references/importCallExpressionAsyncES6System.1.normal.js

@@ -42,7 +42,7 @@ System.register([
             });
             _export("cl2", cl2 = class cl2 {
                 constructor(){
-                    (void 0).p = {
+                    this.p = {
                         m: /*#__PURE__*/ _async_to_generator(function*() {
                             const req = yield import('./test') // FOUR
                             ;

crates/swc_ecma_transforms_module/src/system_js.rs

@@ -30,7 +30,7 @@ struct SystemJs {
     export_values: Vec<Box<Expr>>,
     tla: bool,
     enter_async_fn: u32,
-    enter_fn: u32,
+    is_global_this: bool,
     root_fn_decl_idents: Vec<Ident>,
     module_item_meta_list: Vec<ModuleItemMeta>,
     import_idents: Vec<Id>,
@@ -48,9 +48,9 @@ pub fn system_js(unresolved_mark: Mark, config: Config) -> impl Fold {
         export_map: Default::default(),
         export_names: vec![],
         export_values: vec![],
+        is_global_this: true,
         tla: false,
         enter_async_fn: 0,
-        enter_fn: 0,
         root_fn_decl_idents: vec![],
         module_item_meta_list: vec![],
         import_idents: vec![],
@@ -69,14 +69,13 @@ pub fn system_js_with_resolver(
         unresolved_mark,
         resolver: Resolver::Real { base, resolver },
         config,
-
+        is_global_this: true,
         declare_var_idents: vec![],
         export_map: Default::default(),
         export_names: vec![],
         export_values: vec![],
         tla: false,
         enter_async_fn: 0,
-        enter_fn: 0,
         root_fn_decl_idents: vec![],
         module_item_meta_list: vec![],
         import_idents: vec![],
@@ -94,6 +93,19 @@ struct ModuleItemMeta {
 }
 
 impl SystemJs {
+    fn fold_children_with_non_global_this<T>(&mut self, n: T) -> T
+    where
+        T: FoldWith<Self>,
+    {
+        let is_global_this = self.is_global_this;
+
+        self.is_global_this = false;
+        let node = n.fold_children_with(self);
+        self.is_global_this = is_global_this;
+
+        node
+    }
+
     fn export_call(&self, name: JsWord, span: Span, expr: Expr) -> CallExpr {
         CallExpr {
             span,
@@ -568,7 +580,7 @@ impl Fold for SystemJs {
                 Expr::Await(await_expr)
             }
             Expr::This(this_expr) => {
-                if !self.config.allow_top_level_this && self.enter_fn == 0 {
+                if !self.config.allow_top_level_this && self.is_global_this {
                     return *undefined(DUMMY_SP);
                 }
                 Expr::This(this_expr)
@@ -582,15 +594,21 @@ impl Fold for SystemJs {
         if is_async {
             self.enter_async_fn += 1;
         }
-        self.enter_fn += 1;
         let fold_fn_expr = fn_decl.fold_children_with(self);
         if is_async {
             self.enter_async_fn -= 1;
         }
-        self.enter_fn -= 1;
         fold_fn_expr
     }
 
+    fn fold_class_expr(&mut self, n: ClassExpr) -> ClassExpr {
+        self.fold_children_with_non_global_this(n)
+    }
+
+    fn fold_function(&mut self, n: Function) -> Function {
+        self.fold_children_with_non_global_this(n)
+    }
+
     fn fold_prop(&mut self, prop: Prop) -> Prop {
         match prop {
             Prop::Shorthand(shorthand) => Prop::KeyValue(KeyValueProp {

crates/swc_ecma_transforms_module/tests/system_js.rs

@@ -46,6 +46,72 @@ test!(
     });"#
 );
 
+test!(
+    syntax(),
+    |tester| tr(
+        tester,
+        Config {
+            allow_top_level_this: false
+        }
+    ),
+    iife,
+    r#"
+    (function(a) {
+        this.foo = a;
+    })(this);
+    "#,
+    r#"System.register([], function(_export, _context) {
+        "use strict";
+        return {
+            setters: [],
+            execute: function() {
+                (function(a) {
+                    this.foo = a;
+                })(void 0);
+            }
+        };
+    });"#
+);
+
+test!(
+    syntax(),
+    |tester| tr(
+        tester,
+        Config {
+            allow_top_level_this: false
+        }
+    ),
+    top_level_this_false_class,
+    r#"
+    const a = this;
+    class A {
+        constructor() {
+          this.a = 1;
+        }
+        test() {
+          this.a = 2;
+        }
+    }"#,
+    r#"System.register([], function(_export, _context) {
+        "use strict";
+        var A, a;
+        return {
+            setters: [],
+            execute: function() {
+                a = void 0;
+                A = class A {
+                    constructor(){
+                        this.a = 1;
+                    }
+                    test() {
+                        this.a = 2;
+                    }
+                };
+            }
+        };
+    });"#
+);
+
 test!(
     syntax(),
     |tester| tr(