From 0b7d65d33197e2cab4e57009c1bc5f6fd590b702 Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Thu, 31 Dec 2020 06:55:05 +0000
Subject: [PATCH] fix corner case with `arguments` (#4486)

fixes #4485
---
 lib/compress.js                 |  4 +-
 test/compress/default-values.js | 86 ++++++++++++++++++++++++++++++++
 test/compress/destructured.js   | 87 +++++++++++++++++++++++++++++++++
 3 files changed, 176 insertions(+), 1 deletion(-)

diff --git a/lib/compress.js b/lib/compress.js
index aea3155a..531c9aad 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -3344,7 +3344,9 @@ merge(Compressor.prototype, {
             if (is_undeclared_ref(this) && this.is_declared(compressor)) return false;
             if (this.is_immutable()) return false;
             var def = this.definition();
-            if (is_arguments(def)) return def.scope.uses_arguments > 2;
+            if (is_arguments(def) && all(def.scope.argnames, function(argname) {
+                return argname instanceof AST_SymbolFunarg;
+            })) return def.scope.uses_arguments > 2;
             var fixed = this.fixed_value();
             if (!fixed) return true;
             this._dot_throw = return_true;
diff --git a/test/compress/default-values.js b/test/compress/default-values.js
index 5b21ae6a..ec7c10ff 100644
--- a/test/compress/default-values.js
+++ b/test/compress/default-values.js
@@ -1227,3 +1227,89 @@ issue_4483: {
     expect_stdout: "PASS"
     node_version: ">=6"
 }
+
+issue_4485_1: {
+    options = {
+        pure_getters: "strict",
+        side_effects: true,
+    }
+    input: {
+        (function(a = null) {
+            var arguments;
+            try {
+                arguments.length;
+            } catch (e) {
+                console.log("PASS");
+            }
+        })();
+    }
+    expect: {
+        (function(a = null) {
+            var arguments;
+            try {
+                arguments.length;
+            } catch (e) {
+                console.log("PASS");
+            }
+        })();
+    }
+    expect_stdout: true
+    node_version: ">=6"
+}
+
+issue_4485_2: {
+    options = {
+        pure_getters: "strict",
+        side_effects: true,
+    }
+    input: {
+        (function(a = null) {
+            var arguments = null;
+            try {
+                arguments.length;
+            } catch (e) {
+                console.log("PASS");
+            }
+        })();
+    }
+    expect: {
+        (function(a = null) {
+            var arguments = null;
+            try {
+                arguments.length;
+            } catch (e) {
+                console.log("PASS");
+            }
+        })();
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_4485_3: {
+    options = {
+        unused: true,
+    }
+    input: {
+        (function(a = null) {
+            var arguments;
+            try {
+                arguments.length;
+            } catch (e) {
+                console.log("PASS");
+            }
+        })();
+    }
+    expect: {
+        (function(a = null) {
+            var arguments;
+            try {
+                arguments.length;
+            } catch (e) {
+                console.log("PASS");
+            }
+        })();
+    }
+    expect_stdout: true
+    node_version: ">=6"
+}
diff --git a/test/compress/destructured.js b/test/compress/destructured.js
index ba7dbf3c..c506e8f0 100644
--- a/test/compress/destructured.js
+++ b/test/compress/destructured.js
@@ -2215,3 +2215,90 @@ issue_4456: {
     expect_stdout: "PASS"
     node_version: ">=6"
 }
+
+issue_4485_1: {
+    options = {
+        pure_getters: "strict",
+        side_effects: true,
+    }
+    input: {
+        (function([]) {
+            var arguments;
+            try {
+                arguments.length;
+            } catch (e) {
+                console.log("PASS");
+            }
+        })([]);
+    }
+    expect: {
+        (function([]) {
+            var arguments;
+            try {
+                arguments.length;
+            } catch (e) {
+                console.log("PASS");
+            }
+        })([]);
+    }
+    expect_stdout: true
+    node_version: ">=6"
+}
+
+issue_4485_2: {
+    options = {
+        pure_getters: "strict",
+        side_effects: true,
+    }
+    input: {
+        (function([]) {
+            var arguments = null;
+            try {
+                arguments.length;
+            } catch (e) {
+                console.log("PASS");
+            }
+        })([]);
+    }
+    expect: {
+        (function([]) {
+            var arguments = null;
+            try {
+                arguments.length;
+            } catch (e) {
+                console.log("PASS");
+            }
+        })([]);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_4485_3: {
+    options = {
+        keep_fargs: false,
+        unused: true,
+    }
+    input: {
+        (function([]) {
+            var arguments;
+            try {
+                arguments.length;
+            } catch (e) {
+                console.log("PASS");
+            }
+        })([]);
+    }
+    expect: {
+        (function([]) {
+            var arguments;
+            try {
+                arguments.length;
+            } catch (e) {
+                console.log("PASS");
+            }
+        })([]);
+    }
+    expect_stdout: true
+    node_version: ">=6"
+}