fix(es/minifier): Avoid dropping statements which has side-effects (#6476)

Author: hyf0

crates/swc/tests/tsc-references/objectSpreadSetonlyAccessor.2.minified.js

@@ -1 +1,6 @@
 //// [objectSpreadSetonlyAccessor.ts]
+({
+    ...{
+        set foo (_v){}
+    }
+});

crates/swc_atoms/words.txt

@@ -1369,3 +1369,4 @@ ychannelselector
 yield
 zoomAndPan
 zoomandpan
+__proto__

crates/swc_ecma_minifier/src/compress/optimize/mod.rs

@@ -1918,15 +1918,23 @@ where
             #[cfg(feature = "debug")]
             let start = dump(&n.expr, true);
 
-            let expr = self.ignore_return_value(&mut n.expr);
-            n.expr = expr.map(Box::new).unwrap_or_else(|| {
-                report_change!("visit_mut_expr_stmt: Dropped an expression statement");
-
-                #[cfg(feature = "debug")]
-                dump_change_detail!("Removed {}", start);
-
-                undefined(DUMMY_SP)
-            });
+            // Fix https://github.com/swc-project/swc/issues/6422
+            let is_object_lit_with_spread = n
+                .expr
+                .as_object()
+                .map(|object_lit| object_lit.props.iter().any(|prop| prop.is_spread()))
+                .unwrap_or(false);
+
+            if !is_object_lit_with_spread {
+                let expr = self.ignore_return_value(&mut n.expr);
+                n.expr = expr.map(Box::new).unwrap_or_else(|| {
+                    report_change!("visit_mut_expr_stmt: Dropped an expression statement");
+                    #[cfg(feature = "debug")]
+                    dump_change_detail!("Removed {}", start);
+
+                    undefined(DUMMY_SP)
+                });
+            }
         } else {
             match &mut *n.expr {
                 Expr::Seq(e) => {

crates/swc_ecma_minifier/tests/fixture/issues/6422/1/config.json

@@ -0,0 +1,5 @@
+{
+    "collapse_vars": true,
+    "unused": true,
+    "toplevel": true
+}

crates/swc_ecma_minifier/tests/fixture/issues/6422/1/input.js

@@ -0,0 +1,21 @@
+let getter_effect = 'FAIL';
+let setter_effect = 'FAIL';
+let proto = {
+    get foo() {
+        getter_effect = 'PASS';
+    },
+    set bar(value) {
+        setter_effect = 'PASS';
+    }
+};
+let obj1 = {
+    __proto__: proto
+};
+let obj2 = {
+    __proto__: proto
+};
+let unused = obj1.foo;
+obj2.bar = 0;
+
+assert.strictEqual(getter_effect, 'PASS');
+assert.strictEqual(setter_effect, 'PASS');

crates/swc_ecma_minifier/tests/fixture/issues/6422/1/output.js

@@ -0,0 +1,18 @@
+let getter_effect = 'FAIL';
+let setter_effect = 'FAIL';
+let proto = {
+    get foo () {
+        getter_effect = 'PASS';
+    },
+    set bar (value){
+        setter_effect = 'PASS';
+    }
+};
+({
+    __proto__: proto
+}).foo;
+({
+    __proto__: proto
+}).bar = 0;
+assert.strictEqual(getter_effect, 'PASS');
+assert.strictEqual(setter_effect, 'PASS');

crates/swc_ecma_minifier/tests/fixture/issues/6422/2/config.json

@@ -0,0 +1,4 @@
+{
+    "toplevel": true,
+    "unused": true
+}

crates/swc_ecma_minifier/tests/fixture/issues/6422/2/input.js

@@ -0,0 +1,10 @@
+import assert from 'assert'
+let result = 'FAIL';
+const unused = {
+    ...{
+        get prop() {
+            result = 'PASS';
+        }
+    }
+};
+assert.strictEqual(result, 'PASS');

crates/swc_ecma_minifier/tests/fixture/issues/6422/2/output.js

@@ -0,0 +1,10 @@
+import assert from 'assert';
+let result = 'FAIL';
+({
+    ...{
+        get prop () {
+            result = 'PASS';
+        }
+    }
+});
+assert.strictEqual(result, 'PASS');

crates/swc_ecma_minifier/tests/fixture/issues/6422/3/config.json

@@ -0,0 +1,4 @@
+{
+    "toplevel": true,
+    "unused": true
+}

crates/swc_ecma_minifier/tests/fixture/issues/6422/3/input.js

@@ -0,0 +1,18 @@
+import assert from 'assert'
+let result = 0;
+const unused = {
+    ...{
+        get prop() {
+            result = 1;
+        }
+    },
+    [assert.strictEqual(result, 1)]: null,
+    [result = 2]: null,
+    [assert.strictEqual(result, 2)]: null,
+    ...{
+        get prop() {
+            result = 3;
+        }
+    }
+};
+assert.strictEqual(result, 3);

crates/swc_ecma_minifier/tests/fixture/issues/6422/3/output.js

@@ -0,0 +1,18 @@
+import assert from 'assert';
+let result = 0;
+({
+    ...{
+        get prop () {
+            result = 1;
+        }
+    },
+    [assert.strictEqual(result, 1)]: null,
+    [result = 2]: null,
+    [assert.strictEqual(result, 2)]: null,
+    ...{
+        get prop () {
+            result = 3;
+        }
+    }
+});
+assert.strictEqual(result, 3);

crates/swc_ecma_utils/src/lib.rs

@@ -1375,18 +1375,33 @@ pub trait ExprExt {
                         }
                     }
                     Expr::Object(obj) => {
-                        let is_static_accessor = |prop: &PropOrSpread| {
-                            if let PropOrSpread::Prop(prop) = prop {
-                                if let Prop::Getter(_) | Prop::Setter(_) = &**prop {
-                                    true
-                                } else {
-                                    false
-                                }
-                            } else {
-                                false
-                            }
+                        let can_have_side_effect = |prop: &PropOrSpread| match prop {
+                            PropOrSpread::Spread(_) => true,
+                            PropOrSpread::Prop(prop) => match prop.as_ref() {
+                                Prop::Getter(_)
+                                | Prop::Setter(_)
+                                | Prop::Method(_)
+                                | Prop::Shorthand(Ident {
+                                    sym: js_word!("__proto__"),
+                                    ..
+                                })
+                                | Prop::KeyValue(KeyValueProp {
+                                    key:
+                                        PropName::Ident(Ident {
+                                            sym: js_word!("__proto__"),
+                                            ..
+                                        })
+                                        | PropName::Str(Str {
+                                            value: js_word!("__proto__"),
+                                            ..
+                                        })
+                                        | PropName::Computed(_),
+                                    ..
+                                }) => true,
+                                _ => false,
+                            },
                         };
-                        if obj.props.iter().any(is_static_accessor) {
+                        if obj.props.iter().any(can_have_side_effect) {
                             return true;
                         }
                     }