feat(es/minifier): Inline for loop variables (#7445)

Author: Austaras

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

@@ -9,12 +9,9 @@ for (let _ref of array){
         "x"
     ]);
 }
-for (var _ref of array){
-    var _ref1;
-    _object_without_properties(_ref1 = _ref, [
-        "x"
-    ]), { x: xx  } = _ref1;
-}
+for (var _ref of array)_object_without_properties(_ref, [
+    "x"
+]), { x: xx  } = _ref;
 for (let norest of array.map((a)=>_object_spread_props(_object_spread({}, a), {
         x: 'a string'
     })))norest.x, norest.y;

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

@@ -1,73 +1 @@
-use swc_ecma_ast::*;
 
-use super::Optimizer;
-use crate::mode::Mode;
-
-/// Methods related to the option `collapse_vars`.
-impl<M> Optimizer<'_, M>
-where
-    M: Mode,
-{
-    pub(super) fn collapse_assignment_to_vars(&mut self, e: &mut Expr) {
-        if !self.options.collapse_vars {
-            return;
-        }
-        if self.ctx.in_asm {
-            return;
-        }
-
-        if self.ctx.in_try_block || self.ctx.executed_multiple_time || self.ctx.in_cond {
-            return;
-        }
-
-        if let Expr::Assign(assign @ AssignExpr { op: op!("="), .. }) = &*e {
-            //
-            let left = match &assign.left {
-                PatOrExpr::Expr(_) => return,
-                PatOrExpr::Pat(left) => match &**left {
-                    Pat::Ident(i) => i,
-                    _ => return,
-                },
-            };
-
-            if let Some(usage) = self.data.vars.get(&left.to_id()) {
-                if !usage.declared
-                    || !usage.is_fn_local
-                    || usage.assign_count != 1
-                    || usage.var_kind == Some(VarDeclKind::Const)
-                    || usage.mutated
-                {
-                    return;
-                }
-
-                if usage.executed_multiple_time || usage.used_in_cond {
-                    match &*assign.right {
-                        Expr::Lit(..) | Expr::Ident(..) => {}
-                        _ => return,
-                    }
-                }
-
-                if usage.usage_count >= 2 {
-                    match &*assign.right {
-                        Expr::Lit(..) => {}
-                        _ => return,
-                    }
-                }
-            }
-
-            let value = match &*assign.right {
-                Expr::Lit(Lit::Str(s)) if s.value.len() > 3 => return,
-                Expr::Lit(..) => assign.right.clone(),
-                _ => return,
-            };
-
-            report_change!(
-                "collapse_vars: Decided to inline {}{:?}",
-                left.id.sym,
-                left.id.span.ctxt
-            );
-
-            self.vars.lits.insert(left.to_id(), value);
-        }
-    }
-}

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

@@ -189,24 +189,35 @@ where
                         ..
                     }) => false,
 
-                    Expr::Ident(id) if !id.eq_ignore_span(ident) && usage.assigned_fn_local => self
-                        .data
-                        .vars
-                        .get(&id.to_id())
-                        .filter(|a| {
-                            !a.reassigned() && a.declared && {
+                    Expr::Ident(id) if !id.eq_ignore_span(ident) => {
+                        if !usage.assigned_fn_local {
+                            false
+                        } else if let Some(u) = self.data.vars.get(&id.to_id()) {
+                            let mut should_inline = !u.reassigned() && u.declared;
+
+                            should_inline &=
                                 // Function declarations are hoisted
                                 //
                                 // As we copy expressions, this can cause a problem.
                                 // See https://github.com/swc-project/swc/issues/6463
                                 //
                                 // We check callee_count of `usage` because we copy simple functions
-                                !a.used_above_decl
-                                    || !a.declared_as_fn_decl
-                                    || usage.callee_count == 0
+                                !u.used_above_decl
+                                    || !u.declared_as_fn_decl
+                                    || usage.callee_count == 0;
+
+                            if u.declared_as_for_init && !usage.is_fn_local {
+                                should_inline &= !matches!(
+                                    u.var_kind,
+                                    Some(VarDeclKind::Let | VarDeclKind::Const)
+                                )
                             }
-                        })
-                        .is_some(),
+
+                            should_inline
+                        } else {
+                            false
+                        }
+                    }
 
                     Expr::Lit(lit) => match lit {
                         Lit::Str(s) => {
@@ -228,9 +239,10 @@ where
                     }) => arg.is_lit(),
                     Expr::This(..) => usage.is_fn_local,
                     Expr::Arrow(arr) => {
-                        !(usage.used_as_arg && ref_count > 1)
-                            && is_arrow_simple_enough_for_copy(arr)
-                            && !usage.has_property_mutation
+                        is_arrow_simple_enough_for_copy(arr)
+                            && !(usage.has_property_mutation
+                                || usage.executed_multiple_time
+                                || usage.used_as_arg && ref_count > 1)
                     }
                     _ => false,
                 }

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

@@ -1866,8 +1866,6 @@ where
             }
         }
 
-        self.collapse_assignment_to_vars(e);
-
         if e.is_seq() {
             debug_assert_valid(e);
         }

crates/swc_ecma_minifier/src/program_data.rs

@@ -74,6 +74,8 @@ pub(crate) struct VarUsageInfo {
     pub(crate) declared_as_fn_decl: bool,
     pub(crate) declared_as_fn_expr: bool,
 
+    pub(crate) declared_as_for_init: bool,
+
     pub(crate) assign_count: u32,
     pub(crate) mutation_by_call_count: u32,
 
@@ -144,6 +146,7 @@ impl Default for VarUsageInfo {
             declared_as_fn_param: Default::default(),
             declared_as_fn_decl: Default::default(),
             declared_as_fn_expr: Default::default(),
+            declared_as_for_init: Default::default(),
             assign_count: Default::default(),
             mutation_by_call_count: Default::default(),
             usage_count: Default::default(),
@@ -436,6 +439,10 @@ impl VarDataLike for VarUsageInfo {
         self.declared_as_fn_expr = true;
     }
 
+    fn mark_declared_as_for_init(&mut self) {
+        self.declared_as_for_init = true;
+    }
+
     fn mark_has_property_access(&mut self) {
         self.has_property_access = true;
     }

crates/swc_ecma_minifier/src/util/mod.rs

@@ -355,6 +355,22 @@ impl Visit for IdentUsageCollector {
         n.visit_children_with(self);
     }
 
+    fn visit_getter_prop(&mut self, n: &GetterProp) {
+        if self.ignore_nested {
+            return;
+        }
+
+        n.visit_children_with(self);
+    }
+
+    fn visit_setter_prop(&mut self, n: &SetterProp) {
+        if self.ignore_nested {
+            return;
+        }
+
+        n.visit_children_with(self);
+    }
+
     fn visit_ident(&mut self, n: &Ident) {
         self.ids.insert(n.to_id());
     }

crates/swc_ecma_minifier/tests/benches-full/echarts.js

@@ -3700,8 +3700,8 @@
         scope.mounted[nativeEventName] = listener, scope.listenerOpts[nativeEventName] = opt, addEventListener(scope.domTarget, nativeEventName, listener, opt);
     }
     function unmountDOMEventListeners(scope) {
-        var el, name, handler, opt, mounted = scope.mounted;
-        for(var nativeEventName in mounted)mounted.hasOwnProperty(nativeEventName) && (el = scope.domTarget, name = nativeEventName, handler = mounted[nativeEventName], opt = scope.listenerOpts[nativeEventName], isDomLevel2 ? el.removeEventListener(name, handler, opt) : el.detachEvent('on' + name, handler));
+        var el, handler, opt, mounted = scope.mounted;
+        for(var nativeEventName in mounted)mounted.hasOwnProperty(nativeEventName) && (el = scope.domTarget, handler = mounted[nativeEventName], opt = scope.listenerOpts[nativeEventName], isDomLevel2 ? el.removeEventListener(nativeEventName, handler, opt) : el.detachEvent('on' + nativeEventName, handler));
         scope.mounted = {};
     }
     var DOMHandlerScope = function(domTarget, domHandlers) {

crates/swc_ecma_minifier/tests/fixture/next/react-pdf-renderer/output.js

@@ -18489,10 +18489,10 @@
                         var r = "undefined" != typeof Uint8Array && "undefined" != typeof Uint16Array && "undefined" != typeof Int32Array;
                         t.assign = function(e) {
                             for(var t = Array.prototype.slice.call(arguments, 1); t.length;){
-                                var r, n = t.shift();
-                                if (n) {
-                                    if ("object" != typeof n) throw TypeError(n + "must be non-object");
-                                    for(var i in n)r = i, Object.prototype.hasOwnProperty.call(n, r) && (e[i] = n[i]);
+                                var r = t.shift();
+                                if (r) {
+                                    if ("object" != typeof r) throw TypeError(r + "must be non-object");
+                                    for(var n in r)Object.prototype.hasOwnProperty.call(r, n) && (e[n] = r[n]);
                                 }
                             }
                             return e;

crates/swc_ecma_minifier/tests/fixture/next/styled-components/1/output.js

@@ -4799,8 +4799,8 @@
                     return i;
                 }
                 return _e(e) ? "" : N(e) ? "." + e.styledComponentId : b(e) ? "function" != typeof e || e.prototype && e.prototype.isReactComponent || !n ? e : Ne(e(n), n, r, o) : e instanceof ve ? r ? (e.inject(r, o), e.getName(o)) : e : S(e) ? function e(t, n) {
-                    var r, o, s = [];
-                    for(var i in t)t.hasOwnProperty(i) && !_e(t[i]) && (Array.isArray(t[i]) && t[i].isCss || b(t[i]) ? s.push(be(i) + ":", t[i], ";") : S(t[i]) ? s.push.apply(s, e(t[i], i)) : s.push(be(i) + ": " + (r = i, null == (o = t[i]) || "boolean" == typeof o || "" === o ? "" : "number" != typeof o || 0 === o || r in unitless_browser_esm ? String(o).trim() : o + "px") + ";"));
+                    var o, s = [];
+                    for(var i in t)t.hasOwnProperty(i) && !_e(t[i]) && (Array.isArray(t[i]) && t[i].isCss || b(t[i]) ? s.push(be(i) + ":", t[i], ";") : S(t[i]) ? s.push.apply(s, e(t[i], i)) : s.push(be(i) + ": " + (null == (o = t[i]) || "boolean" == typeof o || "" === o ? "" : "number" != typeof o || 0 === o || i in unitless_browser_esm ? String(o).trim() : o + "px") + ";"));
                     return n ? [
                         n + " {"
                     ].concat(s, [
@@ -4899,8 +4899,8 @@
                             this._foldedDefaultProps = o ? function Me(e) {
                                 for(var t = arguments.length, n = Array(t > 1 ? t - 1 : 0), r = 1; r < t; r++)n[r - 1] = arguments[r];
                                 for(var o = 0; o < n.length; o++){
-                                    var e1, i = n[o];
-                                    if (Ve(i)) for(var a in i)"__proto__" !== (e1 = a) && "constructor" !== e1 && "prototype" !== e1 && function(e, t, n) {
+                                    var i = n[o];
+                                    if (Ve(i)) for(var a in i)"__proto__" !== a && "constructor" !== a && "prototype" !== a && function(e, t, n) {
                                         var r = e[n];
                                         Ve(t) && Ve(r) ? Me(r, t) : e[n] = t;
                                     }(e, i[a], a);

crates/swc_ecma_minifier/tests/fixture/pr/7145/input.js

@@ -0,0 +1,7 @@
+export function foo(arr) {
+    var a = () => x;
+
+    for (const b in arr) {
+        console.log(a);
+    }
+}

crates/swc_ecma_minifier/tests/fixture/pr/7145/output.js

@@ -0,0 +1,4 @@
+export function foo(arr) {
+    var a = ()=>x;
+    for(const b in arr)console.log(a);
+}

crates/swc_ecma_minifier/tests/fixture/reduced/2/output.js

@@ -8,10 +8,7 @@ export const def = {
         const properties = allProps.filter((p)=>!(0, util_1.alwaysValidSchema)(it, schema[p]));
         if (0 === properties.length) return;
         const valid = gen.name("valid");
-        for (const prop1 of properties){
-            var prop;
-            (prop = prop1, it.opts.useDefaults && !it.compositeRule && void 0 !== schema[prop].default) ? applyPropertySchema(prop1) : (gen.if((0, code_1.propertyInData)(gen, data, prop1, it.opts.ownProperties)), applyPropertySchema(prop1), it.allErrors || gen.else().var(valid, !0), gen.endIf()), cxt.it.definedProperties.add(prop1), cxt.ok(valid);
-        }
+        for (const prop of properties)it.opts.useDefaults && !it.compositeRule && void 0 !== schema[prop].default ? applyPropertySchema(prop) : (gen.if((0, code_1.propertyInData)(gen, data, prop, it.opts.ownProperties)), applyPropertySchema(prop), it.allErrors || gen.else().var(valid, !0), gen.endIf()), cxt.it.definedProperties.add(prop), cxt.ok(valid);
         function applyPropertySchema(prop) {
             cxt.subschema({
                 keyword: "properties",

crates/swc_ecma_minifier/tests/full/feedback-mapbox/2c796e83-0724e2af5f19128a/output.js

@@ -3190,21 +3190,11 @@
                         $: expression
                     };
                 case "object":
-                    for(var key in expression)"$" == key ? function() {
-                        if (expression[key]) {
-                            var path = key;
-                            predicates.push(function(value) {
-                                return search(value, expression[path]);
-                            });
-                        }
-                    }() : function() {
-                        if (void 0 !== expression[key]) {
-                            var path = key;
-                            predicates.push(function(value) {
-                                return search(getter(value, path), expression[path]);
-                            });
-                        }
-                    }();
+                    for(var key in expression)"$" == key ? expression[key] && predicates.push(function(value) {
+                        return search(value, expression[key]);
+                    }) : void 0 !== expression[key] && predicates.push(function(value) {
+                        return search(getter(value, key), expression[key]);
+                    });
                     break;
                 case "function":
                     predicates.push(expression);

crates/swc_ecma_minifier/tests/projects/output/angular-1.2.5.js

@@ -111,6 +111,7 @@ where
         let Ctx {
             in_left_of_for_loop,
             in_pat_of_param,
+            in_pat_of_var_decl,
             ..
         } = self.ctx;
 
@@ -126,9 +127,8 @@ where
                 v.mark_declared_as_fn_param();
             }
 
-            if in_left_of_for_loop {
-                v.mark_reassigned();
-                v.mark_mutated();
+            if in_pat_of_var_decl && in_left_of_for_loop {
+                v.mark_declared_as_for_init();
             }
         } else {
             self.report_usage(i, true);

crates/swc_ecma_usage_analyzer/src/analyzer/mod.rs

@@ -51,6 +51,8 @@ pub trait VarDataLike: Sized {
 
     fn mark_declared_as_fn_expr(&mut self);
 
+    fn mark_declared_as_for_init(&mut self);
+
     fn mark_has_property_access(&mut self);
 
     fn mark_has_property_mutation(&mut self);