feat(es/compat): Implement decorator metadata proposal (#8097)

**Description:**

This PR implements the [decorator
metadata](https://github.com/tc39/proposal-decorator-metadata) proposal,
that is now at Stage 3.

As the decorator metadata proposal is a small extension of the decorator
proposal and is not possible to compile the metadata without transpiling
decorators, I opted to implement it into the existing decorator
transformer (and helper)

**Related issue:**

 - Closes #7957

crates/swc_ecma_transforms_base/src/helpers/_apply_decs_2203_r.js

@@ -35,6 +35,7 @@ function applyDecs2203RFactory() {
         kind,
         isStatic,
         isPrivate,
+        metadata,
         value
     ) {
         var kindStr;
@@ -61,6 +62,7 @@ function applyDecs2203RFactory() {
             name: isPrivate ? "#" + name : name,
             static: isStatic,
             private: isPrivate,
+            metadata: metadata,
         };
 
         var decoratorFinishedRef = { v: false };
@@ -168,7 +170,8 @@ function applyDecs2203RFactory() {
         kind,
         isStatic,
         isPrivate,
-        initializers
+        initializers,
+        metadata
     ) {
         var decs = decInfo[0];
 
@@ -221,6 +224,7 @@ function applyDecs2203RFactory() {
                 kind,
                 isStatic,
                 isPrivate,
+                metadata,
                 value
             );
 
@@ -251,6 +255,7 @@ function applyDecs2203RFactory() {
                     kind,
                     isStatic,
                     isPrivate,
+                    metadata,
                     value
                 );
 
@@ -345,7 +350,7 @@ function applyDecs2203RFactory() {
         }
     }
 
-    function applyMemberDecs(Class, decInfos) {
+    function applyMemberDecs(Class, decInfos, metadata) {
         var ret = [];
         var protoInitializers;
         var staticInitializers;
@@ -415,7 +420,8 @@ function applyDecs2203RFactory() {
                 kind,
                 isStatic,
                 isPrivate,
-                initializers
+                initializers,
+                metadata
             );
         }
 
@@ -435,7 +441,7 @@ function applyDecs2203RFactory() {
         }
     }
 
-    function applyClassDecs(targetClass, classDecs) {
+    function applyClassDecs(targetClass, classDecs, metadata) {
         if (classDecs.length > 0) {
             var initializers = [];
             var newClass = targetClass;
@@ -452,6 +458,7 @@ function applyDecs2203RFactory() {
                             initializers,
                             decoratorFinishedRef
                         ),
+                        metadata,
                     });
                 } finally {
                     decoratorFinishedRef.v = true;
@@ -464,7 +471,7 @@ function applyDecs2203RFactory() {
             }
 
             return [
-                newClass,
+                defineMetadata(newClass, metadata),
                 function () {
                     for (var i = 0; i < initializers.length; i++) {
                         initializers[i].call(newClass);
@@ -476,6 +483,14 @@ function applyDecs2203RFactory() {
         // so we don't have to return an empty array here.
     }
 
+    function defineMetadata(Class, metadata) {
+        return Object.defineProperty(
+            Class,
+            Symbol.metadata || Symbol.for("Symbol.metadata"),
+            { configurable: true, enumerable: true, value: metadata }
+        );
+    }
+
     /**
     Basic usage:
   
@@ -622,21 +637,31 @@ function applyDecs2203RFactory() {
     initializeClass(Class);
    */
 
-    return function applyDecs2203R(targetClass, memberDecs, classDecs) {
+    return function applyDecs2203R(targetClass, memberDecs, classDecs, parentClass) {
+        if (parentClass !== void 0) {
+            var parentMetadata =
+                parentClass[Symbol.metadata || Symbol.for("Symbol.metadata")];
+        }
+        var metadata = Object.create(
+            parentMetadata === void 0 ? null : parentMetadata
+        );
+        var e = applyMemberDecs(targetClass, memberDecs, metadata);
+        if (!classDecs.length) defineMetadata(targetClass, metadata);
         return {
-            e: applyMemberDecs(targetClass, memberDecs),
+            e: e,
             // Lazily apply class decorations so that member init locals can be properly bound.
             get c() {
-                return applyClassDecs(targetClass, classDecs);
+                return applyClassDecs(targetClass, classDecs, metadata);
             },
         };
     };
 }
 
-function _apply_decs_2203_r(targetClass, memberDecs, classDecs) {
+function _apply_decs_2203_r(targetClass, memberDecs, classDecs, parentClass) {
     return (_apply_decs_2203_r = applyDecs2203RFactory())(
         targetClass,
         memberDecs,
-        classDecs
+        classDecs,
+        parentClass
     );
-}
+}

crates/swc_ecma_transforms_proposal/src/decorator_2022_03.rs

@@ -9,8 +9,9 @@ use swc_common::{util::take::Take, Spanned, SyntaxContext, DUMMY_SP};
 use swc_ecma_ast::*;
 use swc_ecma_transforms_base::{helper, helper_expr};
 use swc_ecma_utils::{
-    constructor::inject_after_super, default_constructor, prepend_stmt, private_ident,
-    prop_name_to_expr_value, quote_ident, replace_ident, ExprFactory, IdentExt, IdentRenamer,
+    alias_ident_for, constructor::inject_after_super, default_constructor, prepend_stmt,
+    private_ident, prop_name_to_expr_value, quote_ident, replace_ident, ExprFactory, IdentExt,
+    IdentRenamer,
 };
 use swc_ecma_visit::{as_folder, noop_visit_mut_type, Fold, VisitMut, VisitMutWith};
 
@@ -53,6 +54,8 @@ struct ClassState {
 
     class_lhs: Vec<Option<Pat>>,
     class_decorators: Vec<Option<ExprOrSpread>>,
+
+    super_class: Option<Ident>,
 }
 
 impl Decorator202203 {
@@ -154,6 +157,10 @@ impl Decorator202203 {
             .as_arg(),
         );
 
+        if let Some(super_class) = self.state.super_class.as_ref() {
+            combined_args.push(super_class.clone().as_arg());
+        }
+
         let e_pat = if e_lhs.is_empty() {
             None
         } else {
@@ -323,6 +330,27 @@ impl Decorator202203 {
         unreachable!()
     }
 
+    fn handle_super_class(&mut self, class: &mut Class) {
+        if let Some(super_class) = class.super_class.take() {
+            let id = alias_ident_for(&super_class, "_super");
+            self.extra_vars.push(VarDeclarator {
+                span: DUMMY_SP,
+                name: Pat::Ident(id.clone().into()),
+                init: None,
+                definite: false,
+            });
+
+            class.super_class = Some(Box::new(Expr::Assign(AssignExpr {
+                span: DUMMY_SP,
+                op: AssignOp::Assign,
+                left: PatOrExpr::Pat(Box::new(Pat::Ident(id.clone().into()))),
+                right: super_class,
+            })));
+
+            self.state.super_class = Some(id);
+        }
+    }
+
     fn handle_class_expr(&mut self, class: &mut Class, ident: Option<&Ident>) -> Ident {
         debug_assert!(
             !class.decorators.is_empty(),
@@ -361,6 +389,7 @@ impl Decorator202203 {
 
         let decorators = self.preserve_side_effect_of_decorators(class.decorators.take());
         self.state.class_decorators.extend(decorators);
+        self.handle_super_class(class);
 
         {
             let call_stmt = CallExpr {
@@ -417,6 +446,7 @@ impl Decorator202203 {
             self.state.class_lhs.push(Some(init_class.clone().into()));
 
             self.state.class_decorators.extend(decorators);
+            self.handle_super_class(&mut c.class);
 
             let mut body = c.class.body.take();
 

crates/swc_ecma_transforms_proposal/tests/decorators/2022-03-classes--to-es2015/expressions-static-blocks/output.js

@@ -1,5 +1,5 @@
 var _A, __, __1, __2, _C, __3, __11, __21, _class, __4, __12, __22, _class1, __5, __13, __23, _G, __6, __14, __24, _class2, __7, __15, __25, _class3, __8, __16, __26, _K, __9, __17, __27;
-var _initClass, _A1, _initClass1, _C1, _initClass2, _class4, _initClass3, _class5, _initClass4, _G1, _initClass5, _class6, _initClass6, _class7, _initClass7, _K1;
+var _initClass, _A1, _initClass1, _C1, _initClass2, _class4, _initClass3, _class5, _initClass4, _G1, _initClass5, _class6, _initClass6, _class7, _I, _initClass7, _K1, _L;
 const dec = ()=>{};
 const A = ((_A = class A {
 }, __ = {
@@ -81,25 +81,25 @@ const F = [
         value: _initClass5()
     }, _class2), _class6)
 ];
-const H = ((_class3 = class extends I {
+const H = ((_class3 = class extends (_I = I) {
 }, __8 = {
     writable: true,
     value: { c: [_class7, _initClass6] } = _apply_decs_2203_r(_class3, [], [
         dec
-    ])
+    ], _I)
 }, __16 = {
     writable: true,
     value: (()=>{})()
 }, __26 = {
     writable: true,
     value: _initClass6()
 }, _class3), _class7);
-const J = ((_K = class K extends L {
+const J = ((_K = class K extends (_L = L) {
 }, __9 = {
     writable: true,
     value: { c: [_K1, _initClass7] } = _apply_decs_2203_r(_K, [], [
         dec
-    ])
+    ], _L)
 }, __17 = {
     writable: true,
     value: (()=>{})()

crates/swc_ecma_transforms_proposal/tests/decorators/2022-03-classes--to-es2015/expressions/output.js

@@ -1,5 +1,5 @@
 var _A, __, __1, _C, __2, __11, _class, __3, __12, _class1, __4, __13, _G, __5, __14, _class2, __6, __15, _class3, __7, __16, _K, __8, __17;
-var _initClass, _A1, _initClass1, _C1, _initClass2, _class4, _initClass3, _class5, _initClass4, _G1, _initClass5, _class6, _initClass6, _class7, _initClass7, _K1;
+var _initClass, _A1, _initClass1, _C1, _initClass2, _class4, _initClass3, _class5, _initClass4, _G1, _initClass5, _class6, _initClass6, _class7, _I, _initClass7, _K1, _L;
 const dec = ()=>{};
 const A = ((_A = class A {
 }, __ = {
@@ -63,22 +63,22 @@ const F = [
         value: _initClass5()
     }, _class2), _class6)
 ];
-const H = ((_class3 = class extends I {
+const H = ((_class3 = class extends (_I = I) {
 }, __7 = {
     writable: true,
     value: { c: [_class7, _initClass6] } = _apply_decs_2203_r(_class3, [], [
         dec
-    ])
+    ], _I)
 }, __16 = {
     writable: true,
     value: _initClass6()
 }, _class3), _class7);
-const J = ((_K = class K extends L {
+const J = ((_K = class K extends (_L = L) {
 }, __8 = {
     writable: true,
     value: { c: [_K1, _initClass7] } = _apply_decs_2203_r(_K, [], [
         dec
-    ])
+    ], _L)
 }, __17 = {
     writable: true,
     value: _initClass7()

crates/swc_ecma_transforms_proposal/tests/decorators/2022-03-classes--to-es2015/inheritance/output.js

@@ -1,12 +1,12 @@
-var _initClass, _initClass1;
+var _initClass, _initClass1, _Bar;
 const dec1 = ()=>{};
 const dec2 = ()=>{};
-let _Bar;
+let _Bar1;
 class Bar {
 }
 var __ = {
     writable: true,
-    value: { c: [_Bar, _initClass] } = _apply_decs_2203_r(Bar, [], [
+    value: { c: [_Bar1, _initClass] } = _apply_decs_2203_r(Bar, [], [
         dec1
     ])
 };
@@ -15,13 +15,13 @@ var __1 = {
     value: _initClass()
 };
 let _Foo;
-class Foo extends _Bar {
+class Foo extends (_Bar = _Bar1) {
 }
 var __2 = {
     writable: true,
     value: { c: [_Foo, _initClass1] } = _apply_decs_2203_r(Foo, [], [
         dec2
-    ])
+    ], _Bar)
 };
 var __11 = {
     writable: true,

crates/swc_ecma_transforms_proposal/tests/decorators/2022-03-classes--to-es2015/initializers/output.js

@@ -1,10 +1,10 @@
 var _class, __, _class1, __1;
-var _initClass, _initClass1;
+var _initClass, _initClass1, _Foo;
 const dec = ()=>{};
-let _Foo;
+let _Foo1;
 new (_class = class extends _identity {
     constructor(){
-        super(_Foo), _initClass();
+        super(_Foo1), _initClass();
     }
 }, __ = {
     writable: true,
@@ -13,7 +13,7 @@ new (_class = class extends _identity {
         }
         var __ = {
             writable: true,
-            value: { c: [_Foo, _initClass] } = _apply_decs_2203_r(Foo, [], [
+            value: { c: [_Foo1, _initClass] } = _apply_decs_2203_r(Foo, [], [
                 dec
             ])
         };
@@ -28,13 +28,14 @@ new (_class1 = class extends _identity {
 }, __1 = {
     writable: true,
     value: (()=>{
-        class Bar extends _Foo {
+        var _ref;
+        class Bar extends (_ref = _Foo = _Foo1) {
         }
         var __ = {
             writable: true,
             value: { c: [_Bar, _initClass1] } = _apply_decs_2203_r(Bar, [], [
                 dec
-            ])
+            ], _Foo)
         };
         _define_property(Bar, "field", ((()=>{
             Bar.otherField = 456;