improve synergy between compress and rename (#2755)

lib/minify.js

@@ -141,7 +141,6 @@ function minify(files, options) {
         }
         if (timings) timings.rename = Date.now();
         if (options.rename) {
-            SymbolDef.next_id = 1;
             toplevel.figure_out_scope(options.mangle);
             toplevel.expand_names(options.mangle);
         }

lib/scope.js

@@ -464,59 +464,55 @@ AST_Toplevel.DEFMETHOD("mangle_names", function(options){
     }
 });
 
-AST_Toplevel.DEFMETHOD("find_unique_prefix", function(options) {
-    var letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$_";
+AST_Toplevel.DEFMETHOD("find_colliding_names", function(options) {
     var cache = options.cache && options.cache.props;
-    var prefixes = Object.create(null);
-    options.reserved.forEach(add_prefix);
+    var avoid = Object.create(null);
+    options.reserved.forEach(to_avoid);
     this.globals.each(add_def);
     this.walk(new TreeWalker(function(node) {
         if (node instanceof AST_Scope) node.variables.each(add_def);
         if (node instanceof AST_SymbolCatch) add_def(node.definition());
     }));
-    var prefix, i = 0;
-    do {
-        prefix = create_name(i++);
-    } while (prefixes[prefix]);
-    return prefix;
+    return avoid;
 
-    function add_prefix(name) {
-        if (/[0-9]$/.test(name)) {
-            prefixes[name.replace(/[0-9]+$/, "")] = true;
-        }
+    function to_avoid(name) {
+        avoid[name] = true;
     }
 
     function add_def(def) {
         var name = def.name;
         if (def.global && cache && cache.has(name)) name = cache.get(name);
         else if (!def.unmangleable(options)) return;
-        add_prefix(name);
-    }
-
-    function create_name(num) {
-        var name = "";
-        do {
-            name += letters[num % letters.length];
-            num = Math.floor(num / letters.length);
-        } while (num);
-        return name;
+        to_avoid(name);
     }
 });
 
 AST_Toplevel.DEFMETHOD("expand_names", function(options) {
+    base54.reset();
+    base54.sort();
     options = this._default_mangler_options(options);
-    var prefix = this.find_unique_prefix(options);
+    var avoid = this.find_colliding_names(options);
+    var cname = 0;
     this.globals.each(rename);
     this.walk(new TreeWalker(function(node) {
         if (node instanceof AST_Scope) node.variables.each(rename);
         if (node instanceof AST_SymbolCatch) rename(node.definition());
     }));
 
+    function next_name() {
+        var name;
+        do {
+            name = base54(cname++);
+        } while (avoid[name] || !is_identifier(name));
+        return name;
+    }
+
     function rename(def) {
-        if (def.global || def.unmangleable(options)) return;
+        if (def.global && options.cache) return;
+        if (def.unmangleable(options)) return;
         if (member(def.name, options.reserved)) return;
         var d = def.redefined();
-        def.name = d ? d.name : prefix + def.id;
+        def.name = d ? d.name : next_name();
         def.orig.forEach(function(sym) {
             sym.name = def.name;
         });

test/mocha/minify.js

@@ -383,7 +383,7 @@ describe("minify", function() {
                         toplevel: true,
                     },
                     rename: true,
-                }).code, "var a2;(a2=y)(a2);");
+                }).code, "var a;(a=y)(a);");
             }
         });
     });