feat(es/typescript): Add native_class_properties to skip reordering of class properties inits

.changeset/neat-humans-reply.md

@@ -0,0 +1,7 @@
+---
+swc_core: patch
+swc_fast_ts_strip: patch
+swc_ecma_transforms_typescript: minor
+---
+
+feat(es/typescript): Add `native_class_properties ` to skip reordering of class properties inits

crates/swc_ecma_transforms/tests/deno.rs

@@ -36,6 +36,7 @@ fn run_test(input: PathBuf) {
                 typescript(
                     typescript::Config {
                         verbatim_module_syntax: false,
+                        native_class_properties: false,
                         import_not_used_as_values: typescript::ImportsNotUsedAsValues::Remove,
                         no_empty_export: true,
                         import_export_assign_config:

crates/swc_ecma_transforms_typescript/src/config.rs

@@ -3,9 +3,15 @@ use serde::{Deserialize, Serialize};
 #[derive(Debug, Default, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
 pub struct Config {
+    /// https://www.typescriptlang.org/tsconfig#verbatimModuleSyntax
     #[serde(default)]
     pub verbatim_module_syntax: bool,
 
+    /// Native class properties support
+    #[serde(default)]
+    pub native_class_properties: bool,
+
+    /// https://www.typescriptlang.org/tsconfig/#importsNotUsedAsValues
     #[serde(default)]
     pub import_not_used_as_values: ImportsNotUsedAsValues,
 

crates/swc_ecma_transforms_typescript/src/transform.rs

@@ -59,6 +59,7 @@ pub(crate) struct Transform {
     import_export_assign_config: TsImportExportAssignConfig,
     ts_enum_is_mutable: bool,
     verbatim_module_syntax: bool,
+    native_class_properties: bool,
 
     namespace_id: Option<Id>,
     record: TsEnumRecord,
@@ -74,6 +75,7 @@ pub fn transform(
     import_export_assign_config: TsImportExportAssignConfig,
     ts_enum_is_mutable: bool,
     verbatim_module_syntax: bool,
+    native_class_properties: bool,
 ) -> impl Fold + VisitMut {
     as_folder(Transform {
         unresolved_mark,
@@ -82,6 +84,7 @@ pub fn transform(
         import_export_assign_config,
         ts_enum_is_mutable,
         verbatim_module_syntax,
+        native_class_properties,
         ..Default::default()
     })
 }
@@ -139,7 +142,11 @@ impl VisitMut for Transform {
         let init_list = mem::replace(&mut self.in_class_prop_init, init_list);
 
         if !prop_list.is_empty() {
-            self.reorder_class_prop_decls(n, prop_list, init_list);
+            if self.native_class_properties {
+                self.reorder_class_prop_decls(n, prop_list, init_list);
+            } else {
+                self.reorder_class_prop_decls_and_inits(n, prop_list, init_list);
+            }
         }
     }
 
@@ -728,7 +735,7 @@ impl Transform {
 }
 
 impl Transform {
-    fn reorder_class_prop_decls(
+    fn reorder_class_prop_decls_and_inits(
         &mut self,
         class_member_list: &mut Vec<ClassMember>,
         prop_list: Vec<Id>,
@@ -829,6 +836,44 @@ impl Transform {
                 .map(ClassMember::ClassProp),
         );
     }
+
+    fn reorder_class_prop_decls(
+        &mut self,
+        class_member_list: &mut Vec<ClassMember>,
+        prop_list: Vec<Id>,
+        init_list: Vec<Box<Expr>>,
+    ) {
+        if let Some(constructor) = class_member_list
+            .iter_mut()
+            .find_map(|m| m.as_mut_constructor())
+        {
+            inject_after_super(constructor, init_list);
+        }
+
+        class_member_list.splice(
+            0..0,
+            prop_list
+                .into_iter()
+                .map(Ident::from)
+                .map(PropName::from)
+                .map(|key| ClassProp {
+                    span: DUMMY_SP,
+                    key,
+                    value: None,
+                    type_ann: None,
+                    is_static: false,
+                    decorators: Vec::new(),
+                    accessibility: None,
+                    is_abstract: false,
+                    is_optional: false,
+                    is_override: false,
+                    readonly: false,
+                    declare: false,
+                    definite: false,
+                })
+                .map(ClassMember::ClassProp),
+        );
+    }
 }
 
 impl Transform {

crates/swc_ecma_transforms_typescript/src/typescript.rs

@@ -57,6 +57,7 @@ impl VisitMut for TypeScript {
             self.config.import_export_assign_config,
             self.config.ts_enum_is_mutable,
             self.config.verbatim_module_syntax,
+            self.config.native_class_properties,
         ));
 
         if let Some(span) = was_module {

crates/swc_fast_ts_strip/src/lib.rs

@@ -69,10 +69,31 @@ interface Options {
 }
 
 interface TransformConfig {
+    /**
+     * @see https://www.typescriptlang.org/tsconfig#verbatimModuleSyntax
+     */
     verbatimModuleSyntax?: boolean;
+    /**
+     * Native class properties support
+     */
+    nativeClassProperties?: boolean;
     importNotUsedAsValues?: "remove" | "preserve";
+    /**
+     * Don't create `export {}`.
+     * By default, strip creates `export {}` for modules to preserve module
+     * context.
+     * 
+     * @see https://github.com/swc-project/swc/issues/1698
+     */
     noEmptyExport?: boolean;
     importExportAssignConfig?: "Classic" | "Preserve" | "NodeNext" | "EsNext";
+    /**
+     * Disables an optimization that inlines TS enum member values
+     * within the same module that assumes the enum member values
+     * are never modified.
+     * 
+     * Defaults to false.
+     */
     tsEnumIsMutable?: boolean;
 }
 "#;

crates/swc_fast_ts_strip/tests/fixture.rs

@@ -120,6 +120,10 @@ fn opts(mode: Mode) -> Options {
             ..Default::default()
         },
         mode,
+        transform: Some(swc_ecma_transforms_typescript::Config {
+            native_class_properties: true,
+            ..Default::default()
+        }),
         ..Default::default()
     }
 }

crates/swc_fast_ts_strip/tests/fixture/class-properties.js

@@ -0,0 +1,6 @@
+class Foo {
+    x = console.log(1)
+    constructor(public y = console.log(2)) {
+        console.log(3)
+    }
+}

crates/swc_fast_ts_strip/tests/fixture/class-properties.swc-stderr

@@ -0,0 +1,7 @@
+  x TypeScript parameter property is not supported in strip-only mode
+   ,-[3:1]
+ 2 |     x = console.log(1)
+ 3 |     constructor(public y = console.log(2)) {
+   :                        ^^^^^^^^^^^^^^^^^^
+ 4 |         console.log(3)
+   `----

crates/swc_fast_ts_strip/tests/fixture/class-properties.transform.js

@@ -0,0 +1,8 @@
+class Foo {
+    y;
+    x = console.log(1);
+    constructor(y = console.log(2)){
+        this.y = y;
+        console.log(3);
+    }
+}

crates/swc_fast_ts_strip/tests/fixture/class-properties.ts

@@ -0,0 +1,6 @@
+class Foo {
+    x = console.log(1)
+    constructor(public y = console.log(2)) {
+        console.log(3)
+    }
+}