feat(minifier): fold void 1 -> void 0 (#5670)

crates/oxc_ast/src/ast_builder_impl.rs

@@ -108,10 +108,16 @@ impl<'a> AstBuilder<'a> {
 
     /* ---------- Constructors ---------- */
 
+    /// `0`
+    #[inline]
+    pub fn number_0(self) -> Expression<'a> {
+        self.expression_numeric_literal(Span::default(), 0.0, "0", NumberBase::Decimal)
+    }
+
     /// `void 0`
     #[inline]
     pub fn void_0(self) -> Expression<'a> {
-        let num = self.expression_numeric_literal(Span::default(), 0.0, "0", NumberBase::Decimal);
+        let num = self.number_0();
         Expression::UnaryExpression(self.alloc(self.unary_expression(
             Span::default(),
             UnaryOperator::Void,

crates/oxc_minifier/src/ast_passes/fold_constants.rs

@@ -2,7 +2,7 @@
 //!
 //! <https://github.com/google/closure-compiler/blob/master/src/com/google/javascript/jscomp/PeepholeFoldConstants.java>
 
-use std::cmp::Ordering;
+use std::{cmp::Ordering, mem};
 
 use num_bigint::BigInt;
 use oxc_ast::{ast::*, AstBuilder, Visit};
@@ -166,6 +166,7 @@ impl<'a> FoldConstants<'a> {
         ctx: &mut TraverseCtx<'a>,
     ) -> Option<Expression<'a>> {
         match expr.operator {
+            UnaryOperator::Void => Self::try_reduce_void(expr, ctx),
             UnaryOperator::Typeof => self.try_fold_type_of(expr, ctx),
             UnaryOperator::LogicalNot => {
                 expr.argument.to_boolean().map(|b| self.ast.expression_boolean_literal(SPAN, !b))
@@ -182,6 +183,19 @@ impl<'a> FoldConstants<'a> {
         }
     }
 
+    /// `void 1` -> `void 0`
+    fn try_reduce_void(
+        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());
+        }
+        None
+    }
+
     /// Folds 'typeof(foo)' if foo is a literal, e.g.
     /// `typeof("bar") --> "string"`
     /// `typeof(6) --> "number"`

crates/oxc_minifier/tests/ast_passes/fold_constants.rs

@@ -626,7 +626,6 @@ fn test_fold_logical_op2() {
 }
 
 #[test]
-#[ignore]
 fn test_fold_void() {
     test_same("void 0");
     test("void 1", "void 0");