feat(es/minifier): Remove unused parameters of arrow functions (#8636)

**Related issue:** - Closes #8626

Author: kdy1

crates/swc_ecma_minifier/src/compress/optimize/mod.rs

@@ -1454,6 +1454,8 @@ impl VisitMut for Optimizer<'_> {
 
  #[cfg_attr(feature = "debug", tracing::instrument(skip_all))]
  fn visit_mut_arrow_expr(&mut self, n: &mut ArrowExpr) {
+ self.drop_unused_arrow_params(&mut n.params);
+
  let prepend = self.prepend_stmts.take();
 
  let ctx = self.ctx;
@@ -1685,9 +1687,7 @@ impl VisitMut for Optimizer<'_> {
  match n {
  DefaultDecl::Class(_) => {}
  DefaultDecl::Fn(f) => {
- if !self.options.keep_fargs && self.options.unused {
- self.drop_unused_params(&mut f.function.params);
- }
+ self.drop_unused_params(&mut f.function.params);
  }
  DefaultDecl::TsInterfaceDecl(_) => {}
  }
@@ -1708,9 +1708,7 @@ impl VisitMut for Optimizer<'_> {
  #[cfg_attr(feature = "debug", tracing::instrument(skip_all))]
  fn visit_mut_export_decl(&mut self, n: &mut ExportDecl) {
  if let Decl::Fn(f) = &mut n.decl {
- if !self.options.keep_fargs && self.options.unused {
- self.drop_unused_params(&mut f.function.params);
- }
+ self.drop_unused_params(&mut f.function.params);
  }
 
  let ctx = Ctx {
@@ -2027,9 +2025,7 @@ impl VisitMut for Optimizer<'_> {
  .entry(f.ident.to_id())
  .or_insert_with(|| FnMetadata::from(&*f.function));
 
- if !self.options.keep_fargs && self.options.unused {
- self.drop_unused_params(&mut f.function.params);
- }
+ self.drop_unused_params(&mut f.function.params);
 
  let ctx = Ctx {
  top_level: false,

crates/swc_ecma_minifier/src/compress/optimize/unused.rs

@@ -132,13 +132,36 @@ impl Optimizer<'_> {
 
  #[cfg_attr(feature = "debug", tracing::instrument(skip_all))]
  pub(super) fn drop_unused_params(&mut self, params: &mut Vec<Param>) {
+ if self.options.keep_fargs || !self.options.unused {
+ return;
+ }
+
  for param in params.iter_mut().rev() {
  self.take_pat_if_unused(&mut param.pat, None, false);
 
  if !param.pat.is_invalid() {
- return;
+ break;
+ }
+ }
+
+ params.retain(|p| !p.pat.is_invalid());
+ }
+
+ #[cfg_attr(feature = "debug", tracing::instrument(skip_all))]
+ pub(super) fn drop_unused_arrow_params(&mut self, params: &mut Vec<Pat>) {
+ if self.options.keep_fargs || !self.options.unused {
+ return;
+ }
+
+ for param in params.iter_mut().rev() {
+ self.take_pat_if_unused(param, None, false);
+
+ if !param.is_invalid() {
+ break;
  }
  }
+
+ params.retain(|p| !p.is_invalid());
  }
 
  #[cfg_attr(feature = "debug", tracing::instrument(skip_all))]

crates/swc_ecma_minifier/tests/fixture/issues/3126/1/output.js

@@ -1,12 +1,12 @@
 (()=>{
  var __webpack_modules__ = {
- 746: (__unused_webpack_module, __unused_webpack___webpack_exports__, __webpack_require__1)=>{
+ 746: ()=>{
  Object.prototype.hasOwnProperty;
  }
  };
  __webpack_require__.m = __webpack_modules__;
  (()=>{
- __webpack_require__.O = (result, chunkIds, fn, priority)=>{
+ __webpack_require__.O = (result, chunkIds)=>{
  for(var j = 0; j < chunkIds.length; j++)Object.keys(__webpack_require__.O).every((key)=>__webpack_require__.O[key](chunkIds[j]));
  };
  })();

crates/swc_ecma_minifier/tests/fixture/issues/8626/config.json

@@ -0,0 +1,4 @@
+{
+ "defaults": true,
+ "keep_fargs": false
+}

crates/swc_ecma_minifier/tests/fixture/issues/8626/input.js

@@ -0,0 +1,5 @@
+export function foo(cb) {
+ cb();
+}
+
+foo((a, b) => true);

crates/swc_ecma_minifier/tests/fixture/issues/8626/output.js

@@ -0,0 +1,4 @@
+export function foo(cb) {
+ cb();
+}
+foo(()=>!0);