feat(transformer/typescript): support removeClassFieldsWithoutInitializer option (#10576)

* close #9192
* close #10491

We've discussed adding `removeClassFieldsWithoutInitializer` option to support removing class fields without an initializer in #10491 (comment). This is used to align the`TypeScript`'s `useDefineForClassFields: false` option.

Author: Dunqing

crates/oxc_transformer/src/typescript/annotations.rs

@@ -27,6 +27,7 @@ pub struct TypeScriptAnnotations<'a, 'ctx> {
     has_jsx_fragment: bool,
     jsx_element_import_name: String,
     jsx_fragment_import_name: String,
+    remove_class_fields_without_initializer: bool,
 }
 
 impl<'a, 'ctx> TypeScriptAnnotations<'a, 'ctx> {
@@ -52,6 +53,8 @@ impl<'a, 'ctx> TypeScriptAnnotations<'a, 'ctx> {
             has_jsx_fragment: false,
             jsx_element_import_name,
             jsx_fragment_import_name,
+            remove_class_fields_without_initializer: options
+                .remove_class_fields_without_initializer,
         }
     }
 }
@@ -227,11 +230,11 @@ impl<'a> Traverse<'a> for TypeScriptAnnotations<'a, '_> {
                     && !method.value.is_typescript_syntax()
             }
             ClassElement::PropertyDefinition(prop) => {
-                if prop.declare {
-                    false
-                } else {
-                    matches!(prop.r#type, PropertyDefinitionType::PropertyDefinition)
-                }
+                matches!(prop.r#type, PropertyDefinitionType::PropertyDefinition)
+                    && !prop.declare
+                    && !(self.remove_class_fields_without_initializer
+                        && prop.value.is_none()
+                        && prop.decorators.is_empty())
             }
             ClassElement::AccessorProperty(prop) => {
                 matches!(prop.r#type, AccessorPropertyType::AccessorProperty)

crates/oxc_transformer/src/typescript/options.rs

@@ -44,6 +44,41 @@ pub struct TypeScriptOptions {
     #[serde(default = "default_as_true")]
     pub allow_declare_fields: bool,
 
+    /// When enabled, class fields without initializers are removed.
+    ///
+    /// For example:
+    /// ```ts
+    /// class Foo {
+    ///    x: number;
+    ///    y: number = 0;
+    /// }
+    /// ```
+    /// // transform into
+    /// ```js
+    /// class Foo {
+    ///    x: number;
+    /// }
+    /// ```
+    ///
+    /// The option is used to align with the behavior of TypeScript's `useDefineForClassFields: false` option.
+    /// When you want to enable this, you also need to set [`crate::CompilerAssumptions::set_public_class_fields`]
+    /// to `true`. The `set_public_class_fields: true` + `remove_class_fields_without_initializer: true` is
+    /// equivalent to `useDefineForClassFields: false` in TypeScript.
+    ///
+    /// When `set_public_class_fields` is true and class-properties plugin is enabled, the above example transforms into:
+    ///
+    /// ```js
+    /// class Foo {
+    ///   constructor() {
+    ///     this.y = 0;
+    ///   }
+    /// }
+    /// ```
+    ///
+    /// Defaults to `false`.
+    #[serde(default)]
+    pub remove_class_fields_without_initializer: bool,
+
     /// Unused.
     pub optimize_const_enums: bool,
 
@@ -66,6 +101,7 @@ impl Default for TypeScriptOptions {
             only_remove_type_imports: false,
             allow_namespaces: default_as_true(),
             allow_declare_fields: default_as_true(),
+            remove_class_fields_without_initializer: false,
             optimize_const_enums: false,
             rewrite_import_extensions: None,
         }

napi/transform/src/transformer.rs

@@ -252,6 +252,8 @@ impl From<TypeScriptOptions> for oxc::transformer::TypeScriptOptions {
             allow_namespaces: options.allow_namespaces.unwrap_or(ops.allow_namespaces),
             allow_declare_fields: options.allow_declare_fields.unwrap_or(ops.allow_declare_fields),
             optimize_const_enums: false,
+            // TODO: Implement
+            remove_class_fields_without_initializer: false,
             rewrite_import_extensions: options.rewrite_import_extensions.and_then(|value| {
                 match value {
                     Either::A(v) => {

tasks/transform_conformance/snapshots/oxc.snap.md

@@ -1,6 +1,6 @@
 commit: 578ac4df
 
-Passed: 150/246
+Passed: 153/249
 
 # All Passed:
 * babel-plugin-transform-class-static-block
@@ -44,7 +44,7 @@ after transform: SymbolId(0): [ReferenceId(0), ReferenceId(2), ReferenceId(6), R
 rebuilt        : SymbolId(0): [ReferenceId(0), ReferenceId(2), ReferenceId(6), ReferenceId(10)]
 
 
-# babel-plugin-transform-typescript (4/20)
+# babel-plugin-transform-typescript (6/22)
 * class-property-definition/input.ts
 Unresolved references mismatch:
 after transform: ["const"]
@@ -424,7 +424,7 @@ after transform: SymbolId(4): ScopeId(1)
 rebuilt        : SymbolId(5): ScopeId(4)
 
 
-# legacy-decorators (2/71)
+# legacy-decorators (3/72)
 * oxc/metadata/bound-type-reference/input.ts
 Symbol reference IDs mismatch for "BoundTypeReference":
 after transform: SymbolId(0): [ReferenceId(1), ReferenceId(3), ReferenceId(4), ReferenceId(5), ReferenceId(6)]

tasks/transform_conformance/tests/babel-plugin-transform-typescript/test/fixtures/remove-class-properties-without-initializer/input.ts

@@ -0,0 +1,6 @@
+class Cls {
+	x: number;
+	y = 1;
+	@dce
+	z: string;
+}

tasks/transform_conformance/tests/babel-plugin-transform-typescript/test/fixtures/remove-class-properties-without-initializer/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": [["transform-typescript", { "removeClassFieldsWithoutInitializer": true }]]
+}

tasks/transform_conformance/tests/babel-plugin-transform-typescript/test/fixtures/remove-class-properties-without-initializer/output.js

@@ -0,0 +1,5 @@
+class Cls {
+  y = 1;
+  @dce
+  z;
+}

tasks/transform_conformance/tests/babel-plugin-transform-typescript/test/fixtures/use-define-for-class-fields/input.ts

@@ -0,0 +1,4 @@
+class Cls {
+	x: number;
+	y = 1;
+}

tasks/transform_conformance/tests/babel-plugin-transform-typescript/test/fixtures/use-define-for-class-fields/options.json

@@ -0,0 +1,14 @@
+{
+  "assumptions": {
+    "setPublicClassFields": true
+  },
+  "plugins": [
+    "transform-class-properties",
+    [
+      "transform-typescript",
+      {
+        "removeClassFieldsWithoutInitializer": true
+      }
+    ]
+  ]
+}

tasks/transform_conformance/tests/babel-plugin-transform-typescript/test/fixtures/use-define-for-class-fields/output.js

@@ -0,0 +1,5 @@
+class Cls {
+  constructor() {
+    this.y = 1;
+  }
+}

tasks/transform_conformance/tests/legacy-decorators/test/fixtures/oxc/with-typescript-remove-class-properties-without-initializer/input.ts

@@ -0,0 +1,6 @@
+class Cls {
+	x: number;
+	y = 1;
+	@dce
+	z: string;
+}

tasks/transform_conformance/tests/legacy-decorators/test/fixtures/oxc/with-typescript-remove-class-properties-without-initializer/options.json

@@ -0,0 +1,11 @@
+{
+  "plugins": [
+    "transform-legacy-decorator",
+    [
+      "transform-typescript",
+      {
+        "removeClassFieldsWithoutInitializer": true
+      }
+    ]
+  ]
+}

tasks/transform_conformance/tests/legacy-decorators/test/fixtures/oxc/with-typescript-remove-class-properties-without-initializer/output.js

@@ -0,0 +1,5 @@
+class Cls {
+  y = 1;
+  z;
+}
+babelHelpers.decorate([dce], Cls.prototype, "z", void 0);