Handle uglify-reserve comments to reserve props

If you want uglify to reserve property names for a specific function, you
may now precede the function with comments containing:
uglify-reserve prop0 prop1 prop2 ... propN
and in that function's scope, these properties will not be mangled.

For example:

// uglify-reserve keepme
function foo() {
    return {
	keepme: "This property will NOT be mangled",
	butme: "This property WILL be mangled"
    };
}

lib/propmangle.js

@@ -87,6 +87,7 @@ function mangle_properties(ast, options) {
     var names_to_mangle = [];
     var unmangleable = [];
     var ignored = {};
+    var function_reserved = Object.create(null);
 
     // step 1: find candidates to mangle
     ast.walk(new TreeWalker(function(node){
@@ -107,6 +108,15 @@ function mangle_properties(ast, options) {
 
     // step 2: transform the tree, renaming properties
     return ast.transform(new TreeTransformer(function(node){
+        if (node instanceof AST_Defun) {
+            function_reserved = Object.create(function_reserved);
+
+            var reserve_props = parse_reserve_comments(node.start.comments_before);
+            reserve_props.forEach(function(prop) {
+                function_reserved[prop] = true;
+            });
+        }
+
         if (node instanceof AST_ObjectKeyVal) {
             if (!(ignore_quoted && node.quote))
                 node.key = mangle(node.key);
@@ -134,6 +144,10 @@ function mangle_properties(ast, options) {
         //         );
         //     }
         // }
+    }, function(node) {
+        if (node instanceof AST_Defun) {
+            function_reserved = Object.getPrototypeOf(function_reserved);
+        }
     }));
 
     // only function declarations after this line
@@ -152,6 +166,8 @@ function mangle_properties(ast, options) {
         if (ignore_quoted && name in ignored) return false;
         if (regex && !regex.test(name)) return false;
         if (reserved.indexOf(name) >= 0) return false;
+        if (name in function_reserved) return false;
+
         return cache.props.has(name)
             || names_to_mangle.indexOf(name) >= 0;
     }
@@ -227,4 +243,21 @@ function mangle_properties(ast, options) {
         }));
     }
 
+    function parse_reserve_comments(comments) {
+        var props = [];
+
+        comments.forEach(function(comment) {
+            var text = comment.value;
+            var reserveRe = /^\s*uglify-reserve (.+)/gm,
+                match;
+
+            while (match = reserveRe.exec(text)) {
+                match[1].split(/\s+/).forEach(function(prop) {
+                    push_uniq(props, prop);
+                });
+            }
+        });
+
+        return props;
+    }
 }

test/compress/reserve-comments.js

@@ -0,0 +1,126 @@
+reserve_single_line: {
+    mangle_props = true
+
+    input: {
+        // noise
+        // uglify-reserve keepme andme
+        // noise
+        function foo() {
+            window.notme = 0;
+            window.keepme = 1;
+            window["andme"] = 1;
+            return { andme: 1, "keepme": 1, butnotme: 0 };
+        }
+        // noise
+        // uglify-reserve keepme
+        //uglify-reserve andme
+        // noise
+        function bar() {
+            window.notme = 0;
+            window.keepme = 1;
+            window["andme"] = 1;
+            return { andme: 1, "keepme": 1, butnotme: 0 };
+        }
+    }
+    expect: {
+        function foo() {
+            window.a = 0;
+            window.keepme = 1;
+            window["andme"] = 1;
+            return { andme: 1, "keepme": 1, b: 0 };
+        }
+        function bar() {
+            window.a = 0;
+            window.keepme = 1;
+            window["andme"] = 1;
+            return { andme: 1, "keepme": 1, b: 0 };
+        }
+    }
+}
+
+reserve_multi_line: {
+    mangle_props = true
+
+    input: {
+        /* uglify-reserve keepme andme*/
+        function foo() {
+            window.notme = 0;
+            window.keepme = 1;
+            window["andme"] = 1;
+            return { andme: 1, "keepme": 1, butnotme: 0 };
+        }
+        /* noise
+               uglify-reserve keepme
+      uglify-reserve andme
+         noise */
+        function bar() {
+            window.notme = 0;
+            window.keepme = 1;
+            window["andme"] = 1;
+            return { andme: 1, "keepme": 1, butnotme: 0 };
+        }
+    }
+    expect: {
+        function foo() {
+            window.a = 0;
+            window.keepme = 1;
+            window["andme"] = 1;
+            return { andme: 1, "keepme": 1, b: 0 };
+        }
+        function bar() {
+            window.a = 0;
+            window.keepme = 1;
+            window["andme"] = 1;
+            return { andme: 1, "keepme": 1, b: 0 };
+        }
+    }
+}
+
+reserve_propagation: {
+    mangle_props = true
+
+    input: {
+        // uglify-reserve thisguy
+        function foo() {
+            // uglify-reserve thatguy
+            function bar() {
+                return {
+                    notme: 0,
+                    thisguy: 1,
+                    thatguy: 1
+                };
+            }
+            return {
+                whome: 0,
+                thisguy: 1,
+                thatguy: 0
+            };
+        }
+        var o = {
+            whome: 0,
+            thisguy: 0,
+            thatguy: 0
+        };
+    }
+    expect: {
+        function foo() {
+            function bar() {
+                return {
+                    a: 0,
+                    thisguy: 1,
+                    thatguy: 1
+                };
+            }
+            return {
+                b: 0,
+                thisguy: 1,
+                c: 0
+            };
+        }
+        var o = {
+            b: 0,
+            d: 0,
+            c: 0
+        };
+    }
+}