From 6c8ee9fdefd0e2541736e9c11002fa1c55ba6f63 Mon Sep 17 00:00:00 2001
From: Boshen <1430279+Boshen@users.noreply.github.com>
Date: Fri, 3 Jan 2025 12:24:57 +0000
Subject: [PATCH] feat(minifier): remove last redundant `return` statement
 (#8234)

---
 .../src/ast_passes/minimize_exit_points.rs    | 25 +++++++++++++++++++
 crates/oxc_minifier/src/ast_passes/mod.rs     |  4 +++
 tasks/minsize/minsize.snap                    | 12 ++++-----
 3 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/crates/oxc_minifier/src/ast_passes/minimize_exit_points.rs b/crates/oxc_minifier/src/ast_passes/minimize_exit_points.rs
index 3792787f51c08..600587a31c011 100644
--- a/crates/oxc_minifier/src/ast_passes/minimize_exit_points.rs
+++ b/crates/oxc_minifier/src/ast_passes/minimize_exit_points.rs
@@ -22,6 +22,10 @@ impl<'a> CompressorPass<'a> for MinimizeExitPoints {
 }
 
 impl<'a> Traverse<'a> for MinimizeExitPoints {
+    fn exit_function_body(&mut self, body: &mut FunctionBody<'a>, _ctx: &mut TraverseCtx<'a>) {
+        self.remove_last_return(&mut body.statements);
+    }
+
     fn exit_statements(&mut self, stmts: &mut Vec<'a, Statement<'a>>, ctx: &mut TraverseCtx<'a>) {
         self.fold_if_return(stmts, ctx);
     }
@@ -32,6 +36,16 @@ impl<'a> MinimizeExitPoints {
         Self { changed: false }
     }
 
+    // `function foo() { return }` -> `function foo() {}`
+    fn remove_last_return(&mut self, stmts: &mut Vec<'a, Statement<'a>>) {
+        if let Some(last) = stmts.last() {
+            if matches!(last, Statement::ReturnStatement(ret) if ret.argument.is_none()) {
+                stmts.pop();
+                self.changed = true;
+            }
+        }
+    }
+
     // `if(x)return;foo` -> `if(!x)foo;`
     fn fold_if_return(&mut self, stmts: &mut Vec<'a, Statement<'a>>, ctx: &mut TraverseCtx<'a>) {
         if stmts.len() <= 1 {
@@ -87,6 +101,8 @@ mod test {
         fold(source_text, source_text);
     }
 
+    // oxc
+
     #[test]
     fn simple() {
         fold(
@@ -109,6 +125,15 @@ mod test {
         fold_same("function foo() { if (foo) return bar; baz }");
     }
 
+    #[test]
+    fn remove_last_return() {
+        fold("function () {return}", "function () {}");
+        fold("function () {a;b;return}", "function () {a;b;}");
+        fold_same("function () { if(foo) { return } }");
+    }
+
+    // closure
+
     #[test]
     #[ignore]
     fn test_break_optimization() {
diff --git a/crates/oxc_minifier/src/ast_passes/mod.rs b/crates/oxc_minifier/src/ast_passes/mod.rs
index fae87b8437b32..50bce420fae90 100644
--- a/crates/oxc_minifier/src/ast_passes/mod.rs
+++ b/crates/oxc_minifier/src/ast_passes/mod.rs
@@ -141,6 +141,10 @@ impl<'a> Traverse<'a> for PeepholeOptimizations {
         self.x6_peephole_substitute_alternate_syntax.exit_return_statement(stmt, ctx);
     }
 
+    fn exit_function_body(&mut self, body: &mut FunctionBody<'a>, ctx: &mut TraverseCtx<'a>) {
+        self.x1_minimize_exit_points.exit_function_body(body, ctx);
+    }
+
     fn exit_variable_declaration(
         &mut self,
         decl: &mut VariableDeclaration<'a>,
diff --git a/tasks/minsize/minsize.snap b/tasks/minsize/minsize.snap
index b8cc4fc06c5a6..5ef32c59a39dc 100644
--- a/tasks/minsize/minsize.snap
+++ b/tasks/minsize/minsize.snap
@@ -1,7 +1,7 @@
            | Oxc        | ESBuild    | Oxc        | ESBuild    |
 Original   | minified   | minified   | gzip       | gzip       | Fixture
 -------------------------------------------------------------------------------------
-72.14 kB   | 23.69 kB   | 23.70 kB   | 8.62 kB    | 8.54 kB    | react.development.js
+72.14 kB   | 23.68 kB   | 23.70 kB   | 8.61 kB    | 8.54 kB    | react.development.js
 
 173.90 kB  | 59.86 kB   | 59.82 kB   | 19.43 kB   | 19.33 kB   | moment.js 
 
@@ -15,13 +15,13 @@ Original   | minified   | minified   | gzip       | gzip       | Fixture
 
 1.01 MB    | 460.32 kB  | 458.89 kB  | 126.85 kB  | 126.71 kB  | bundle.min.js
 
-1.25 MB    | 652.73 kB  | 646.76 kB  | 163.54 kB  | 163.73 kB  | three.js  
+1.25 MB    | 652.68 kB  | 646.76 kB  | 163.53 kB  | 163.73 kB  | three.js  
 
-2.14 MB    | 726.33 kB  | 724.14 kB  | 180.20 kB  | 181.07 kB  | victory.js
+2.14 MB    | 726.19 kB  | 724.14 kB  | 180.18 kB  | 181.07 kB  | victory.js
 
-3.20 MB    | 1.01 MB    | 1.01 MB    | 331.92 kB  | 331.56 kB  | echarts.js
+3.20 MB    | 1.01 MB    | 1.01 MB    | 331.91 kB  | 331.56 kB  | echarts.js
 
-6.69 MB    | 2.32 MB    | 2.31 MB    | 492.82 kB  | 488.28 kB  | antd.js   
+6.69 MB    | 2.32 MB    | 2.31 MB    | 492.81 kB  | 488.28 kB  | antd.js   
 
-10.95 MB   | 3.50 MB    | 3.49 MB    | 909.58 kB  | 915.50 kB  | typescript.js
+10.95 MB   | 3.50 MB    | 3.49 MB    | 909.31 kB  | 915.50 kB  | typescript.js