feat(minifier): remove unused expression in for init and update

crates/oxc_minifier/src/peephole/minimize_conditions.rs

@@ -716,7 +716,7 @@ mod test {
         // Verify function deletion tracking.
         // test("if(!!true||function(){}) {}", "if(1) {}");
         // Don't bother with FOR inits as there are normalized out.
-        test("for(!!true;;) foo()", "for(!0;;) foo()");
+        test("for(!!true;;) foo()", "for(;;) foo()");
 
         // These test tryMinimizeCondition
         test("for(;!!x;) foo()", "for(;x;) foo()");

crates/oxc_minifier/src/peephole/remove_dead_code.rs

@@ -220,6 +220,21 @@ impl<'a, 'b> PeepholeOptimizations {
         for_stmt: &mut ForStatement<'a>,
         ctx: Ctx<'a, 'b>,
     ) -> Option<Statement<'a>> {
+        if let Some(init) = &mut for_stmt.init {
+            if let Some(init) = init.as_expression_mut() {
+                if self.remove_unused_expression(init, ctx) {
+                    for_stmt.init = None;
+                    self.mark_current_function_as_changed();
+                }
+            }
+        }
+        if let Some(update) = &mut for_stmt.update {
+            if self.remove_unused_expression(update, ctx) {
+                for_stmt.update = None;
+                self.mark_current_function_as_changed();
+            }
+        }
+
         let test_boolean =
             for_stmt.test.as_ref().and_then(|test| test.evaluate_value_to_boolean(&ctx));
         if for_stmt.test.as_ref().is_some_and(|test| test.may_have_side_effects(&ctx)) {
@@ -591,4 +606,16 @@ mod test {
         test("while(true) { throw a; unreachable;}", "for(;;) throw a");
         test("while(true) { return a; unreachable;}", "for(;;) return a");
     }
+
+    #[test]
+    fn remove_unused_expressions_in_for() {
+        test(
+            "var i; for (i = 0, 0; i < 10; i++) foo(i);",
+            "var i; for (i = 0; i < 10; i++) foo(i);",
+        );
+        test(
+            "var i; for (i = 0; i < 10; 0, i++, 0) foo(i);",
+            "var i; for (i = 0; i < 10; i++) foo(i);",
+        );
+    }
 }

crates/oxc_minifier/tests/peephole/mod.rs

@@ -57,7 +57,7 @@ fn integration() {
          }
          console.log(c, d);
         ",
-        "if ((() => console.log('effect'))(), !1) for (var c = 1, c; unknownGlobal; unknownGlobal && !0) var d;
+        "if ((() => console.log('effect'))(), !1) for (var c = 1, c; unknownGlobal; unknownGlobal) var d;
         console.log(c, d);
         ",
     );