implement directives (#3203)

fixes #3166

README.md

@@ -666,6 +666,8 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
   enabled `compress` transforms. Useful when you only want to enable a few
   `compress` options while disabling the rest.
 
+- `directives` (default: `true`) -- remove redundant or non-standard directives
+
 - `drop_console` (default: `false`) -- Pass `true` to discard calls to
   `console.*` functions. If you wish to drop a specific function call
   such as `console.info` and/or retain side effects from function arguments

lib/compress.js

@@ -58,6 +58,7 @@ function Compressor(options, false_by_default) {
         conditionals  : !false_by_default,
         dead_code     : !false_by_default,
         defaults      : true,
+        directives    : !false_by_default,
         drop_console  : false,
         drop_debugger : !false_by_default,
         ecma          : 5,
@@ -3211,8 +3212,10 @@ merge(Compressor.prototype, {
 
     /* -----[ optimizers ]----- */
 
+    var directives = ["use asm", "use strict"];
     OPT(AST_Directive, function(self, compressor) {
-        if (compressor.has_directive(self.value) !== self) {
+        if (compressor.option("directives")
+            && (!member(self.value, directives) || compressor.has_directive(self.value) !== self)) {
             return make_node(AST_EmptyStatement, self);
         }
         return self;

test/compress/directives.js

@@ -1,4 +1,7 @@
 class_directives_compression: {
+    options = {
+        directives: true,
+    }
     input: {
         class foo {
             foo() {

test/compress/functions.js

@@ -2246,6 +2246,37 @@ issue_2898: {
     expect_stdout: "2"
 }
 
+deduplicate_parenthesis: {
+    input: {
+        ({}).a = b;
+        (({}).a = b)();
+        (function() {}).a = b;
+        ((function() {}).a = b)();
+    }
+    expect_exact: "({}).a=b;({}.a=b)();(function(){}).a=b;(function(){}.a=b)();"
+}
+
+issue_3166: {
+    options = {
+        directives: true,
+    }
+    input: {
+        "foo";
+        "use strict";
+        function f() {
+            "use strict";
+            "bar";
+            "use asm";
+        }
+    }
+    expect: {
+        "use strict";
+        function f() {
+            "use asm";
+        }
+    }
+}
+
 issue_3016_1: {
     options = {
         inline: true,
@@ -2507,6 +2538,7 @@ issue_3125: {
 
 drop_lone_use_strict: {
     options = {
+        directives: true,
         side_effects: true,
     }
     input: {
@@ -2537,6 +2569,7 @@ drop_lone_use_strict: {
 drop_lone_use_strict_arrows_1: {
     options = {
         side_effects: true,
+        directives: true,
     }
     input: {
         var f0 = () => 0;
@@ -2594,13 +2627,3 @@ drop_lone_use_strict_arrows_2: {
     }
     node_version: ">=6"
 }
-
-deduplicate_parenthesis: {
-    input: {
-        ({}).a = b;
-        (({}).a = b)();
-        (function() {}).a = b;
-        ((function() {}).a = b)();
-    }
-    expect_exact: "({}).a=b;({}.a=b)();(function(){}).a=b;(function(){}.a=b)();"
-}

test/mocha/cli.js

@@ -9,7 +9,7 @@ function read(path) {
 
 describe("bin/uglifyjs", function() {
     var uglifyjscmd = '"' + process.argv[0] + '" bin/uglifyjs';
-    it("should produce a functional build when using --self", function (done) {
+    it("Should produce a functional build when using --self", function (done) {
         this.timeout(120000);
 
         var command = uglifyjscmd + ' --self -mc ecma=';
@@ -70,7 +70,7 @@ describe("bin/uglifyjs", function() {
             done();
         });
     });
-    it("should not append source map to output when not using --source-map url=inline", function (done) {
+    it("Should not append source map to output when not using --source-map url=inline", function (done) {
         var command = uglifyjscmd + ' test/input/issue-1323/sample.js';
 
         exec(command, function (err, stdout) {
@@ -80,7 +80,7 @@ describe("bin/uglifyjs", function() {
             done();
         });
     });
-    it("should not consider source map file content as source map file name (issue #2082)", function (done) {
+    it("Should not consider source map file content as source map file name (issue #2082)", function (done) {
         var command = [
             uglifyjscmd,
             "test/input/issue-2082/sample.js",