fix(minifier): compute void number as undefined (#6028)

crates/oxc_minifier/examples/minifier.rs

@@ -23,11 +23,13 @@ fn main() -> std::io::Result<()> {
     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);
+    let mut allocator = Allocator::default();
+    let printed = minify(&allocator, &source_text, source_type, mangle);
     println!("{printed}");
 
     if twice {
-        let printed2 = minify(&printed, source_type, mangle);
+        allocator.reset();
+        let printed2 = minify(&allocator, &printed, source_type, mangle);
         println!("{printed2}");
         println!("same = {}", printed == printed2);
     }
@@ -35,11 +37,15 @@ fn main() -> std::io::Result<()> {
     Ok(())
 }
 
-fn minify(source_text: &str, source_type: SourceType, mangle: bool) -> String {
+fn minify(
-    let allocator = Allocator::default();
+    allocator: &Allocator,
-    let ret = Parser::new(&allocator, source_text, source_type).parse();
+    source_text: &str,
-    let program = allocator.alloc(ret.program);
+    source_type: SourceType,
-    let options = MinifierOptions { mangle, compress: CompressOptions::all_true() };
+    mangle: bool,
-    let ret = Minifier::new(options).build(&allocator, program);
+) -> String {
-    CodeGenerator::new().with_mangler(ret.mangler).build(program).source_text
+    let ret = Parser::new(allocator, source_text, source_type).parse();
+    let mut program = ret.program;
+    let options = MinifierOptions { mangle, compress: CompressOptions::default() };
+    let ret = Minifier::new(options).build(allocator, &mut program);
+    CodeGenerator::new().with_mangler(ret.mangler).build(&program).source_text
 }

crates/oxc_minifier/src/ast_passes/peephole_fold_constants.rs

@@ -1,4 +1,4 @@
-use std::{cmp::Ordering, mem};
+use std::cmp::Ordering;
 
 use num_bigint::BigInt;
 use oxc_ast::ast::*;
@@ -105,12 +105,12 @@ impl<'a> PeepholeFoldConstants {
     }
 
     fn try_fold_unary_expression(
-        &self,
+        &mut self,
         expr: &mut UnaryExpression<'a>,
         ctx: &mut TraverseCtx<'a>,
     ) -> Option<Expression<'a>> {
         match expr.operator {
-            UnaryOperator::Void => Self::try_reduce_void(expr, ctx),
+            UnaryOperator::Void => self.try_reduce_void(expr, ctx),
             UnaryOperator::Typeof => self.try_fold_type_of(expr, ctx),
             #[allow(clippy::float_cmp)]
             UnaryOperator::LogicalNot => {
@@ -135,13 +135,15 @@ impl<'a> PeepholeFoldConstants {
 
     /// `void 1` -> `void 0`
     fn try_reduce_void(
+        &mut self,
         expr: &mut UnaryExpression<'a>,
         ctx: &mut TraverseCtx<'a>,
     ) -> Option<Expression<'a>> {
         if (!expr.argument.is_number() || !expr.argument.is_number_0())
             && !expr.may_have_side_effects()
         {
-            let _ = mem::replace(&mut expr.argument, ctx.ast.number_0());
+            expr.argument = ctx.ast.number_0();
+            self.changed = true;
         }
         None
     }

crates/oxc_minifier/src/ast_passes/peephole_substitute_alternate_syntax.rs

@@ -46,10 +46,10 @@ impl<'a> Traverse<'a> for PeepholeSubstituteAlternateSyntax {
     fn enter_variable_declaration(
         &mut self,
         decl: &mut VariableDeclaration<'a>,
-        _ctx: &mut TraverseCtx<'a>,
+        ctx: &mut TraverseCtx<'a>,
     ) {
         for declarator in decl.declarations.iter_mut() {
-            self.compress_variable_declarator(declarator);
+            self.compress_variable_declarator(declarator, ctx);
         }
     }
 
@@ -247,11 +247,15 @@ impl<'a> PeepholeSubstituteAlternateSyntax {
         }
     }
 
-    fn compress_variable_declarator(&mut self, decl: &mut VariableDeclarator<'a>) {
+    fn compress_variable_declarator(
+        &mut self,
+        decl: &mut VariableDeclarator<'a>,
+        ctx: &mut TraverseCtx<'a>,
+    ) {
         if decl.kind.is_const() {
             return;
         }
-        if decl.init.as_ref().is_some_and(|init| init.is_undefined() || init.is_void_0()) {
+        if decl.init.as_ref().is_some_and(|init| ctx.is_expression_undefined(init)) {
             decl.init = None;
             self.changed = true;
         }

crates/oxc_minifier/src/node_util/mod.rs

@@ -41,10 +41,13 @@ pub trait NodeUtil {
     fn scopes(&self) -> &ScopeTree;
 
     fn is_expression_undefined(&self, expr: &Expression) -> bool {
-        if let Expression::Identifier(ident) = expr {
+        match expr {
-            return self.is_identifier_undefined(ident);
+            Expression::Identifier(ident) if self.is_identifier_undefined(ident) => true,
-        };
+            Expression::UnaryExpression(e) if e.operator.is_void() && e.argument.is_number() => {
-        false
+                true
+            }
+            _ => false,
+        }
     }
 
     fn is_identifier_undefined(&self, ident: &IdentifierReference) -> bool {

crates/oxc_syntax/src/operator.rs

@@ -5,7 +5,7 @@ use oxc_allocator::CloneIn;
 use oxc_ast_macros::ast;
 use oxc_span::{cmp::ContentEq, hash::ContentHash};
 #[cfg(feature = "serialize")]
-use ::{serde::Serialize, tsify::Tsify};
+use {serde::Serialize, tsify::Tsify};
 
 use crate::precedence::{GetPrecedence, Precedence};
 
@@ -356,6 +356,10 @@ impl UnaryOperator {
         matches!(self, Self::BitwiseNot)
     }
 
+    pub fn is_void(self) -> bool {
+        matches!(self, Self::Void)
+    }
+
     pub fn is_keyword(self) -> bool {
         matches!(self, Self::Typeof | Self::Void | Self::Delete)
     }