fix(es/compat): Apply Array.prototype.slice to arguments in loose spread (#11122)

**Related issue:**

 - Closes #11118

Author: magic-akari

.changeset/tender-buses-allow.md

@@ -0,0 +1,5 @@
+---
+swc_ecma_compat_es2015: major
+---
+
+fix(es/compat): Apply `Array.prototype.slice` to `arguments` in loose spread

crates/swc/tests/fixture/issues-10xxx/11118/input/.swcrc

@@ -0,0 +1,19 @@
+{
+  "jsc": {
+    "parser": {
+      "syntax": "ecmascript",
+      "jsx": false
+    },
+    "target": "es5",
+    "loose": true,
+    "minify": {
+      "compress": false,
+      "mangle": false
+    }
+  },
+  "module": {
+    "type": "es6"
+  },
+  "minify": false,
+  "isModule": true
+}

crates/swc/tests/fixture/issues-10xxx/11118/input/index.js

@@ -0,0 +1,5 @@
+function xxx() {
+    const b = [...arguments];
+    const c = [2, ...arguments];
+    return b.length + c.length;
+}

crates/swc/tests/fixture/issues-10xxx/11118/output/index.js

@@ -0,0 +1,7 @@
+function xxx() {
+    var b = [].concat(Array.prototype.slice.call(arguments));
+    var c = [].concat([
+        2
+    ], Array.prototype.slice.call(arguments));
+    return b.length + c.length;
+}

crates/swc_ecma_compat_es2015/src/lib.rs

@@ -74,7 +74,7 @@ where
             template_literal(c.template_literal),
             classes(c.classes),
             new_target(),
-            spread(c.spread),
+            spread(c.spread, unresolved_mark),
         ),
         // https://github.com/Microsoft/TypeScript/issues/5441
         if !c.typescript {

crates/swc_ecma_compat_es2015/src/spread.rs

@@ -2,7 +2,7 @@ use std::mem;
 
 use serde::Deserialize;
 use swc_atoms::atom;
-use swc_common::{util::take::Take, Span, Spanned, DUMMY_SP};
+use swc_common::{util::take::Take, Mark, Span, Spanned, SyntaxContext, DUMMY_SP};
 use swc_ecma_ast::*;
 use swc_ecma_transforms_base::{ext::ExprRefExt, helper, perf::Check};
 use swc_ecma_transforms_macros::fast_path;
@@ -14,9 +14,11 @@ use swc_ecma_visit::{
 };
 use swc_trace_macro::swc_trace;
 
-pub fn spread(c: Config) -> impl Pass {
+pub fn spread(c: Config, unresolved_mark: Mark) -> impl Pass {
+    let unresolved_ctxt = SyntaxContext::empty().apply_mark(unresolved_mark);
     visit_mut_pass(Spread {
         c,
+        unresolved_ctxt,
         vars: Default::default(),
     })
 }
@@ -28,9 +30,9 @@ pub struct Config {
 }
 
 /// es2015 - `SpreadElement`
-#[derive(Default)]
 struct Spread {
     c: Config,
+    unresolved_ctxt: SyntaxContext,
     vars: Vec<VarDeclarator>,
 }
 
@@ -271,7 +273,7 @@ impl Spread {
             for arg in args.flatten() {
                 let expr = arg.expr;
                 match arg.spread {
-                    Some(_) => {
+                    Some(span) => {
                         if !current_elems.is_empty() {
                             arg_list.push(
                                 ArrayLit {
@@ -282,6 +284,27 @@ impl Spread {
                             );
                             current_elems = Vec::new();
                         }
+                        // Special handling for `arguments` to call Array.prototype.slice
+                        // https://github.com/babel/babel/blob/61ad8555b875cb0c0996f18f803b6bf1d2150173/packages/babel-plugin-transform-spread/src/index.ts#L43-L47
+                        let expr = match *expr {
+                            Expr::Ident(Ident { ref sym, ctxt, .. })
+                                if &**sym == "arguments" && ctxt == self.unresolved_ctxt =>
+                            {
+                                CallExpr {
+                                    span,
+                                    callee: member_expr!(
+                                        Default::default(),
+                                        DUMMY_SP,
+                                        Array.prototype.slice.call
+                                    )
+                                    .as_callee(),
+                                    args: vec![expr.as_arg()],
+                                    ..Default::default()
+                                }
+                                .into()
+                            }
+                            _ => *expr,
+                        };
                         arg_list.push(expr.as_arg());
                     }
                     None => {

crates/swc_ecma_preset_env/src/lib.rs

@@ -253,7 +253,7 @@ where
     let pass = add!(
         pass,
         Spread,
-        es2015::spread(es2015::spread::Config { loose }),
+        es2015::spread(es2015::spread::Config { loose }, unresolved_mark),
         true
     );
     let pass = add!(pass, ObjectSuper, es2015::object_super());

crates/swc_ecma_transforms_compat/tests/es2015_classes.rs

@@ -25,7 +25,7 @@ fn spec_tr(_: &Tester) -> impl Pass {
     (
         resolver(unresolved_mark, Mark::new(), false),
         classes(Default::default()),
-        spread(Default::default()),
+        spread(Default::default(), unresolved_mark),
         block_scoping(unresolved_mark),
     )
 }