From d90000697320fa6ffeea80b77dca9d6cd32d2127 Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Thu, 30 Apr 2020 14:52:57 +0100
Subject: [PATCH] fix corner case in `dead_code` (#3831)

fixes #3830
---
 lib/compress.js            |   1 +
 test/compress/dead-code.js | 202 +++++++++++++++++++++++++++++++++++++
 2 files changed, 203 insertions(+)

diff --git a/lib/compress.js b/lib/compress.js
index 8eb684d3..c679a8b2 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -7532,6 +7532,7 @@ merge(Compressor.prototype, {
                     node = parent;
                     parent = compressor.parent(level++);
                     if (parent instanceof AST_Assign) {
+                        if (parent.left instanceof AST_PropAccess) break;
                         if (!(parent.left instanceof AST_SymbolRef)) continue;
                         if (parent.left.definition() !== def) continue;
                         if (in_try(level, parent)) break;
diff --git a/test/compress/dead-code.js b/test/compress/dead-code.js
index 5de9ad37..5a7be3c7 100644
--- a/test/compress/dead-code.js
+++ b/test/compress/dead-code.js
@@ -949,3 +949,205 @@ issue_3578: {
     }
     expect_stdout: "PASS"
 }
+
+issue_3830_1: {
+    options = {
+        dead_code: true,
+    }
+    input: {
+        var o = {
+            set p(v) {
+                o = o.p = o = v;
+            }
+        };
+        o.p = "PASS";
+        console.log(o);
+    }
+    expect: {
+        var o = {
+            set p(v) {
+                o = o.p = o = v;
+            }
+        };
+        o.p = "PASS";
+        console.log(o);
+    }
+    expect_stdout: "PASS"
+}
+
+issue_3830_2: {
+    options = {
+        dead_code: true,
+    }
+    input: {
+        var a = "FAIL";
+        var o = {
+            set FAIL(v) {
+                a = o[a] = a = v;
+            }
+        };
+        o[a] = "PASS";
+        console.log(a);
+    }
+    expect: {
+        var a = "FAIL";
+        var o = {
+            set FAIL(v) {
+                a = o[a] = a = v;
+            }
+        };
+        o[a] = "PASS";
+        console.log(a);
+    }
+    expect_stdout: "PASS"
+}
+
+issue_3830_3: {
+    options = {
+        dead_code: true,
+    }
+    input: {
+        function f() {
+            return a;
+        }
+        var a = "FAIL";
+        var o = {
+            set FAIL(v) {
+                a = o[f()] = a = v;
+            }
+        };
+        o[f()] = "PASS";
+        console.log(a);
+    }
+    expect: {
+        function f() {
+            return a;
+        }
+        var a = "FAIL";
+        var o = {
+            set FAIL(v) {
+                a = o[f()] = a = v;
+            }
+        };
+        o[f()] = "PASS";
+        console.log(a);
+    }
+    expect_stdout: "PASS"
+}
+
+issue_3830_4: {
+    options = {
+        dead_code: true,
+    }
+    input: {
+        function f() {
+            return o;
+        }
+        var a = "FAIL";
+        var o = {
+            set FAIL(v) {
+                a = f()[a] = a = v;
+            }
+        };
+        f()[a] = "PASS";
+        console.log(a);
+    }
+    expect: {
+        function f() {
+            return o;
+        }
+        var a = "FAIL";
+        var o = {
+            set FAIL(v) {
+                a = f()[a] = a = v;
+            }
+        };
+        f()[a] = "PASS";
+        console.log(a);
+    }
+    expect_stdout: "PASS"
+}
+
+issue_3830_5: {
+    options = {
+        dead_code: true,
+    }
+    input: {
+        function f() {
+            return o;
+        }
+        function g() {
+            return a;
+        }
+        var a = "FAIL";
+        var o = {
+            set FAIL(v) {
+                a = f()[g()] = a = v;
+            }
+        };
+        f()[g()] = "PASS";
+        console.log(a);
+    }
+    expect: {
+        function f() {
+            return o;
+        }
+        function g() {
+            return a;
+        }
+        var a = "FAIL";
+        var o = {
+            set FAIL(v) {
+                a = f()[g()] = a = v;
+            }
+        };
+        f()[g()] = "PASS";
+        console.log(a);
+    }
+    expect_stdout: "PASS"
+}
+
+issue_3830_6: {
+    options = {
+        dead_code: true,
+    }
+    input: {
+        function f() {
+            return o;
+        }
+        function g() {
+            return a;
+        }
+        function h(v) {
+            a = f()[g()] = a = v;
+        }
+        var a = "FAIL";
+        var o = {
+            set FAIL(v) {
+                h(v);
+            }
+        };
+        o.FAIL = "PASS";
+        console.log(a);
+    }
+    expect: {
+        function f() {
+            return o;
+        }
+        function g() {
+            return a;
+        }
+        function h(v) {
+            a = f()[g()] = a = v;
+        }
+        var a = "FAIL";
+        var o = {
+            set FAIL(v) {
+                h(v);
+            }
+        };
+        o.FAIL = "PASS";
+        console.log(a);
+    }
+    expect_stdout: "PASS"
+}
-- 
2.34.1