From cae222c20694012baac66f563a66e8dcf6ce48b2 Mon Sep 17 00:00:00 2001
From: sapphi-red <49056869+sapphi-red@users.noreply.github.com>
Date: Sun, 24 Aug 2025 04:31:52 +0000
Subject: [PATCH] feat(minifier): compress `return void foo()` => `foo();
 return` (#13271)

Compress `return void foo()` => `foo(); return`.
`return void 0` and `return undefined` was handled but this wasn't.
---
 crates/oxc_minifier/src/ctx.rs                |  5 ++++
 .../src/peephole/minimize_statements.rs       | 29 ++++++++++++++++++-
 .../peephole/substitute_alternate_syntax.rs   | 10 ++-----
 tasks/minsize/minsize.snap                    |  2 +-
 4 files changed, 37 insertions(+), 9 deletions(-)

diff --git a/crates/oxc_minifier/src/ctx.rs b/crates/oxc_minifier/src/ctx.rs
index 39f4ed64d6b6c..579fa4021566f 100644
--- a/crates/oxc_minifier/src/ctx.rs
+++ b/crates/oxc_minifier/src/ctx.rs
@@ -13,6 +13,7 @@ use oxc_syntax::{
     identifier::{is_identifier_part, is_identifier_start},
     reference::ReferenceId,
 };
+use oxc_traverse::Ancestor;
 
 use crate::{options::CompressOptions, state::MinifierState, symbol_value::SymbolValue};
 
@@ -253,4 +254,8 @@ impl<'a> Ctx<'a, '_> {
         chars.next().is_some_and(is_identifier_start)
             && chars.all(|c| is_identifier_part(c) && c != '・' && c != '･')
     }
+
+    pub fn is_in_async_generator(&self) -> bool {
+        self.ancestors().any(|ancestor| matches!(ancestor, Ancestor::FunctionBody(body) if *body.r#async() && *body.generator()))
+    }
 }
diff --git a/crates/oxc_minifier/src/peephole/minimize_statements.rs b/crates/oxc_minifier/src/peephole/minimize_statements.rs
index 2d0243c3933b5..0b9606f011bd8 100644
--- a/crates/oxc_minifier/src/peephole/minimize_statements.rs
+++ b/crates/oxc_minifier/src/peephole/minimize_statements.rs
@@ -3,7 +3,10 @@ use std::{iter, ops::ControlFlow};
 use oxc_allocator::{Box, TakeIn, Vec};
 use oxc_ast::ast::*;
 use oxc_ast_visit::Visit;
-use oxc_ecmascript::side_effects::MayHaveSideEffects;
+use oxc_ecmascript::{
+    constant_evaluation::{DetermineValueType, ValueType},
+    side_effects::MayHaveSideEffects,
+};
 use oxc_semantic::ScopeId;
 use oxc_span::{ContentEq, GetSpan};
 use oxc_traverse::Ancestor;
@@ -610,6 +613,30 @@ impl<'a> PeepholeOptimizations {
 
         ctx: &mut Ctx<'a, '_>,
     ) {
+        if let Some(argument) = &mut ret_stmt.argument
+            && argument.value_type(ctx) == ValueType::Undefined
+            // `return undefined` has a different semantic in async generator function.
+            && !ctx.is_in_async_generator()
+        {
+            ctx.state.changed = true;
+            if argument.may_have_side_effects(ctx) {
+                if ctx.options().sequences
+                    && let Some(Statement::ExpressionStatement(prev_expr_stmt)) = result.last_mut()
+                {
+                    let a = &mut prev_expr_stmt.expression;
+                    prev_expr_stmt.expression = Self::join_sequence(a, argument, ctx);
+                } else {
+                    result.push(
+                        ctx.ast.statement_expression(argument.span(), argument.take_in(ctx.ast)),
+                    );
+                }
+            }
+            ret_stmt.argument = None;
+            result.push(Statement::ReturnStatement(ret_stmt));
+            *is_control_flow_dead = true;
+            return;
+        }
+
         if ctx.options().sequences {
             if let Some(Statement::ExpressionStatement(prev_expr_stmt)) = result.last_mut() {
                 if let Some(argument) = &mut ret_stmt.argument {
diff --git a/crates/oxc_minifier/src/peephole/substitute_alternate_syntax.rs b/crates/oxc_minifier/src/peephole/substitute_alternate_syntax.rs
index 604fbb0e3b471..14d6047b89eef 100644
--- a/crates/oxc_minifier/src/peephole/substitute_alternate_syntax.rs
+++ b/crates/oxc_minifier/src/peephole/substitute_alternate_syntax.rs
@@ -790,12 +790,8 @@ impl<'a> PeepholeOptimizations {
             return;
         }
         // `return undefined` has a different semantic in async generator function.
-        for ancestor in ctx.ancestors() {
-            if let Ancestor::FunctionBody(func) = ancestor {
-                if *func.r#async() && *func.generator() {
-                    return;
-                }
-            }
+        if ctx.is_in_async_generator() {
+            return;
         }
         stmt.argument = None;
         ctx.state.changed = true;
@@ -1482,7 +1478,7 @@ mod test {
         test("function f(){return !1;}", "function f(){return !1}");
         test("function f(){return null;}", "function f(){return null}");
         test("function f(){return void 0;}", "function f(){}");
-        test("function f(){return void foo();}", "function f(){return void foo()}");
+        test("function f(){return void foo();}", "function f(){foo()}");
         test("function f(){return undefined;}", "function f(){}");
         test("function f(){if(a()){return undefined;}}", "function f(){a()}");
         test_same("function a(undefined) { return undefined; }");
diff --git a/tasks/minsize/minsize.snap b/tasks/minsize/minsize.snap
index e7a5c8551d9c6..44622ed287e72 100644
--- a/tasks/minsize/minsize.snap
+++ b/tasks/minsize/minsize.snap
@@ -23,5 +23,5 @@ Original   | minified   | minified   | gzip       | gzip       | Iterations | Fi
 
 6.69 MB    | 2.23 MB    | 2.31 MB    | 461.69 kB  | 488.28 kB  |          3 | antd.js    
 
-10.95 MB   | 3.35 MB    | 3.49 MB    | 860.59 kB  | 915.50 kB  |          2 | typescript.js 
+10.95 MB   | 3.35 MB    | 3.49 MB    | 860.58 kB  | 915.50 kB  |          2 | typescript.js