From ace581169134d9b6d4cdf6b24880f7ce122fc88e Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Mon, 26 Feb 2018 15:22:52 +0800
Subject: [PATCH] drop lone "use strict" in function body (#2963)

fixes #2961
---
 lib/compress.js            | 10 ++++++++++
 test/compress/functions.js | 29 +++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/lib/compress.js b/lib/compress.js
index c402e3ba..f9382f0d 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -3024,6 +3024,16 @@ merge(Compressor.prototype, {
         return self;
     });
 
+    OPT(AST_Lambda, function(self, compressor){
+        tighten_body(self.body, compressor);
+        if (compressor.option("side_effects")
+            && self.body.length == 1
+            && self.body[0] === compressor.has_directive("use strict")) {
+            self.body.length = 0;
+        }
+        return self;
+    });
+
     AST_Scope.DEFMETHOD("drop_unused", function(compressor){
         if (!compressor.option("unused")) return;
         if (compressor.has_directive("use asm")) return;
diff --git a/test/compress/functions.js b/test/compress/functions.js
index 5d0be0f9..ddf5fe05 100644
--- a/test/compress/functions.js
+++ b/test/compress/functions.js
@@ -2022,3 +2022,32 @@ deduplicate_parenthesis: {
     }
     expect_exact: "({}).a=b;({}.a=b)();(function(){}).a=b;(function(){}.a=b)();"
 }
+
+drop_lone_use_strict: {
+    options = {
+        side_effects: true,
+    }
+    input: {
+        function f1() {
+            "use strict";
+        }
+        function f2() {
+            "use strict";
+            function f3() {
+                "use strict";
+            }
+        }
+        (function f4() {
+            "use strict";
+        })();
+    }
+    expect: {
+        function f1() {
+        }
+        function f2() {
+            "use strict";
+            function f3() {
+            }
+        }
+    }
+}
-- 
2.34.1