fix corner case in `arguments` (#4396)

fixes #4395

3 files changed, 30 insertions, 1 deletions

diff --git a/lib/compress.js b/lib/compress.js
index b8f4b3a5..4279dc7c 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -9897,7 +9897,10 @@ merge(Compressor.prototype, {
             } else if (argname instanceof AST_Destructured) {
                 argname = null;
             } else if (argname && (compressor.has_directive("use strict")
-                || !(fn_parent instanceof AST_Call && index < fn_parent.args.length))) {
+                || !(fn_parent instanceof AST_Call && index < fn_parent.args.length)
+                || !all(fn.argnames, function(argname) {
+                    return !(argname instanceof AST_Destructured);
+                }))) {
                 var arg_def = argname.definition();
                 if (!compressor.option("reduce_vars")
                     || def.reassigned
diff --git a/test/compress/destructured.js b/test/compress/destructured.js
index 81beb7f7..1c448f2a 100644
--- a/test/compress/destructured.js
+++ b/test/compress/destructured.js
@@ -1886,3 +1886,23 @@ issue_4386: {
     expect_stdout: "PASS"
     node_version: ">=6"
 }
+
+issue_4395: {
+    options = {
+        arguments: true,
+    }
+    input: {
+        console.log(function(a, {}) {
+            a = "FAIL";
+            return arguments[0];
+        }("PASS", 42));
+    }
+    expect: {
+        console.log(function(a, {}) {
+            a = "FAIL";
+            return arguments[0];
+        }("PASS", 42));
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
diff --git a/test/reduce.js b/test/reduce.js
index db4b7521..1ab18411 100644
--- a/test/reduce.js
+++ b/test/reduce.js
@@ -175,6 +175,12 @@ module.exports = function reduce_test(testcase, minify_options, reduce_options)
                     CHANGED = true;
                     return expr instanceof U.AST_Spread ? expr.expression : expr;
                 }
+                if (node.expression instanceof U.AST_Arrow && node.expression.value) {
+                    var seq = node.args.slice();
+                    seq.push(node.expression.value);
+                    CHANGED = true;
+                    return to_sequence(seq);
+                }
                 if (node.expression instanceof U.AST_Function) {
                     // hoist and return expressions from the IIFE function expression
                     var body = node.expression.body;