fix(minifier): fix keep_var keeping vars from arrow functions (#4680)

Cargo.toml

@@ -200,8 +200,8 @@ oxc_macros.opt-level     = 1
 oxc_ast_macros.opt-level = 1
 # Compile insta and its dependencies in release mode for faster snapshot tests
 # See: https://insta.rs/docs/quickstart/#optional-faster-runs
-insta.opt-level          = 3
-similar.opt-level        = 3
+insta.opt-level   = 3
+similar.opt-level = 3
 
 [profile.release.package.oxc_wasm]
 opt-level = 'z'

crates/oxc_minifier/examples/minifier.rs

@@ -2,7 +2,7 @@
 use std::path::Path;
 
 use oxc_allocator::Allocator;
-use oxc_codegen::{CodeGenerator, WhitespaceRemover};
+use oxc_codegen::CodeGenerator;
 use oxc_minifier::{CompressOptions, Minifier, MinifierOptions};
 use oxc_parser::Parser;
 use oxc_span::SourceType;
@@ -17,34 +17,28 @@ fn main() -> std::io::Result<()> {
 
     let name = args.subcommand().ok().flatten().unwrap_or_else(|| String::from("test.js"));
     let mangle = args.contains("--mangle");
-    let whitespace = args.contains("--whitespace");
     let twice = args.contains("--twice");
 
     let path = Path::new(&name);
     let source_text = std::fs::read_to_string(path)?;
     let source_type = SourceType::from_path(path).unwrap();
 
-    let printed = minify(&source_text, source_type, mangle, whitespace);
+    let printed = minify(&source_text, source_type, mangle);
     println!("{printed}");
 
     if twice {
-        let printed = minify(&printed, source_type, mangle, whitespace);
+        let printed = minify(&printed, source_type, mangle);
         println!("{printed}");
     }
 
     Ok(())
 }
 
-fn minify(source_text: &str, source_type: SourceType, mangle: bool, whitespace: bool) -> String {
+fn minify(source_text: &str, source_type: SourceType, mangle: bool) -> String {
     let allocator = Allocator::default();
     let ret = Parser::new(&allocator, source_text, source_type).parse();
     let program = allocator.alloc(ret.program);
     let options = MinifierOptions { mangle, compress: CompressOptions::all_true() };
     let ret = Minifier::new(options).build(&allocator, program);
-    if whitespace {
-        CodeGenerator::new().with_mangler(ret.mangler).build(program)
-    } else {
-        WhitespaceRemover::new().with_mangler(ret.mangler).build(program)
-    }
-    .source_text
+    CodeGenerator::new().with_mangler(ret.mangler).build(program).source_text
 }

crates/oxc_minifier/src/ast_passes/remove_dead_code.rs

@@ -58,7 +58,7 @@ impl<'a> RemoveDeadCode<'a> {
 
         let mut keep_var = KeepVar::new(self.ast);
 
-        for stmt in stmts.iter().skip(index) {
+        for stmt in stmts.iter().skip(index + 1) {
             keep_var.visit_statement(stmt);
         }
 

crates/oxc_minifier/src/keep_var.rs

@@ -21,6 +21,8 @@ impl<'a> Visit<'a> for KeepVar<'a> {
         /* skip functions */
     }
 
+    fn visit_arrow_function_expression(&mut self, _it: &ArrowFunctionExpression<'a>) {}
+
     fn visit_class(&mut self, _it: &Class<'a>) {
         /* skip classes */
     }

crates/oxc_minifier/tests/oxc/remove_dead_code.rs

@@ -18,12 +18,18 @@ fn print(source_text: &str, remove_dead_code: bool) -> String {
         .source_text
 }
 
-pub(crate) fn test(source_text: &str, expected: &str) {
+fn test(source_text: &str, expected: &str) {
     let minified = print(source_text, true);
     let expected = print(expected, false);
     assert_eq!(minified, expected, "for source {source_text}");
 }
 
+fn test_same(source_text: &str) {
+    let minified = print(source_text, true);
+    let expected = print(source_text, false);
+    assert_eq!(minified, expected, "for source {source_text}");
+}
+
 #[test]
 fn dce_if_statement() {
     test("if (true) { foo }", "{ foo }");
@@ -119,6 +125,24 @@ fn dce_logical_expression() {
     test("const foo = true && bar()", "const foo = bar()");
 }
 
+#[test]
+fn dce_var_hoisting() {
+    test_same(
+        "function f() {
+          return () => {
+            var x;
+          }
+        }",
+    );
+    test_same(
+        "function f() {
+          return function g() {
+            var x;
+          }
+        }",
+    );
+}
+
 // https://github.com/terser/terser/blob/master/test/compress/dead-code.js
 #[test]
 fn dce_from_terser() {

tasks/benchmark/Cargo.toml

@@ -111,13 +111,7 @@ lexer = ["dep:oxc_allocator", "dep:oxc_parser", "dep:oxc_span", "dep:oxc_tasks_c
 parser = ["dep:oxc_allocator", "dep:oxc_parser", "dep:oxc_span", "dep:oxc_tasks_common"]
 transformer = ["dep:oxc_allocator", "dep:oxc_parser", "dep:oxc_span", "dep:oxc_tasks_common", "dep:oxc_transformer"]
 semantic = ["dep:oxc_allocator", "dep:oxc_parser", "dep:oxc_semantic", "dep:oxc_span", "dep:oxc_tasks_common"]
-minifier = [
-  "dep:oxc_allocator",
-  "dep:oxc_minifier",
-  "dep:oxc_parser",
-  "dep:oxc_span",
-  "dep:oxc_tasks_common",
-]
+minifier = ["dep:oxc_allocator", "dep:oxc_minifier", "dep:oxc_parser", "dep:oxc_span", "dep:oxc_tasks_common"]
 codegen = ["dep:oxc_allocator", "dep:oxc_codegen", "dep:oxc_parser", "dep:oxc_span", "dep:oxc_tasks_common"]
 sourcemap = [
   "dep:oxc_allocator",