From 7f19211736b727d1591f7165f9503bfec53669f1 Mon Sep 17 00:00:00 2001
From: camc314 <18101008+camc314@users.noreply.github.com>
Date: Mon, 6 Jan 2025 02:21:24 +0000
Subject: [PATCH] feat(minifier): minimize unary expression statements (#8256)

`delete` cannot be minified as it may have side effect.
---
 .../ast_passes/peephole_remove_dead_code.rs   | 35 +++++++++++++++++++
 crates/oxc_syntax/src/operator.rs             |  5 +++
 tasks/minsize/minsize.snap                    |  4 +--
 3 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/crates/oxc_minifier/src/ast_passes/peephole_remove_dead_code.rs b/crates/oxc_minifier/src/ast_passes/peephole_remove_dead_code.rs
index 34f35b33d083c..6e65a5fa6130f 100644
--- a/crates/oxc_minifier/src/ast_passes/peephole_remove_dead_code.rs
+++ b/crates/oxc_minifier/src/ast_passes/peephole_remove_dead_code.rs
@@ -310,6 +310,20 @@ impl<'a, 'b> PeepholeRemoveDeadCode {
                 Expression::FunctionExpression(function_expr) if function_expr.id.is_none() => {
                     Some(ctx.ast.statement_empty(SPAN))
                 }
+                // `typeof x` -> ``
+                Expression::UnaryExpression(unary_expr)
+                    if unary_expr.operator.is_typeof()
+                        && unary_expr.argument.is_identifier_reference() =>
+                {
+                    Some(ctx.ast.statement_empty(SPAN))
+                }
+                // `typeof x.y` -> `x`, `!x` -> `x`, `void x` -> `x`...
+                Expression::UnaryExpression(unary_expr) if !unary_expr.operator.is_delete() => {
+                    Some(ctx.ast.statement_expression(
+                        unary_expr.span,
+                        ctx.ast.move_expression(&mut unary_expr.argument),
+                    ))
+                }
                 _ => None,
             })
     }
@@ -548,4 +562,25 @@ mod test {
         fold("([...a, b, ...c])", "([...a, ...c])");
         fold_same("([...b, ...c])"); // It would also be fine if the spreads were split apart.
     }
+
+    #[test]
+    fn test_fold_unary_expression_statement() {
+        fold("typeof x", "");
+        fold("typeof x?.y", "x?.y");
+        fold("typeof x.y", "x.y");
+        fold("typeof x.y.z()", "x.y.z()");
+        fold("void x", "x");
+        fold("void x?.y", "x?.y");
+        fold("void x.y", "x.y");
+        fold("void x.y.z()", "x.y.z()");
+        fold("!x", "x");
+        fold("!x?.y", "x?.y");
+        fold("!x.y", "x.y");
+        fold("!x.y.z()", "x.y.z()");
+        fold("-x.y.z()", "x.y.z()");
+
+        fold_same("delete x");
+        fold_same("delete x.y");
+        fold_same("delete x.y.z()");
+    }
 }
diff --git a/crates/oxc_syntax/src/operator.rs b/crates/oxc_syntax/src/operator.rs
index 76ac35d9e8bfc..0d295d9204bf0 100644
--- a/crates/oxc_syntax/src/operator.rs
+++ b/crates/oxc_syntax/src/operator.rs
@@ -498,6 +498,11 @@ impl UnaryOperator {
         self == Self::Void
     }
 
+    /// Returns `true` if this is the [`delete`](UnaryOperator::Delete) operator.
+    pub fn is_delete(self) -> bool {
+        self == Self::Delete
+    }
+
     /// Returns `true` if this operator is a keyword instead of punctuation.
     pub fn is_keyword(self) -> bool {
         matches!(self, Self::Typeof | Self::Void | Self::Delete)
diff --git a/tasks/minsize/minsize.snap b/tasks/minsize/minsize.snap
index 36875636bc121..cb8dbf88029b2 100644
--- a/tasks/minsize/minsize.snap
+++ b/tasks/minsize/minsize.snap
@@ -21,7 +21,7 @@ Original   | minified   | minified   | gzip       | gzip       | Fixture
 
 3.20 MB    | 1.01 MB    | 1.01 MB    | 331.90 kB  | 331.56 kB  | echarts.js
 
-6.69 MB    | 2.32 MB    | 2.31 MB    | 492.86 kB  | 488.28 kB  | antd.js   
+6.69 MB    | 2.32 MB    | 2.31 MB    | 492.87 kB  | 488.28 kB  | antd.js   
 
-10.95 MB   | 3.50 MB    | 3.49 MB    | 909.32 kB  | 915.50 kB  | typescript.js
+10.95 MB   | 3.50 MB    | 3.49 MB    | 909.30 kB  | 915.50 kB  | typescript.js