implement AST cloning (fixes #296)

- new function `clone` to deep clone of AST node
- new option `clone` for `compress()` to transform copy of input AST
(useful in case of AST reuse)

README.md

@@ -286,11 +286,14 @@ var ast = csso.parse('.foo.bar', {
 
 #### compress(ast[, options])
 
-Do the main task – compress AST.
+Does the main task – compress AST.
+
+> NOTE: `compress` performs AST compression by transforming input AST by default (since AST cloning is expensive and needed in rare cases). Use `clone` option with truthy value in case you want to keep input AST untouched.
 
 Options:
 
 - restructure `Boolean` – do the structure optimisations or not (`true` by default)
+- clone `Boolean` - transform a copy of input AST if `true`, useful in case of AST reuse (`false` by default)
 - comments `String` or `Boolean` – specify what comments to left
  - `'exclamation'` or `true` (default) – left all exclamation comments (i.e. `/*! .. */`)
  - `'first-exclamation'` – remove every comments except first one

lib/compressor/index.js

@@ -1,4 +1,5 @@
 var List = require('../utils/list');
+var clone = require('../utils/clone');
 var usageUtils = require('./usage');
 var clean = require('./clean');
 var compress = require('./compress');
@@ -83,10 +84,34 @@ function getRestructureOption(options) {
  true;
 }
 
+function wrapBlockAst(block) {
+ return {
+ type: 'StyleSheet',
+ rules: new List([{
+ type: 'Ruleset',
+ selector: {
+ type: 'Selector',
+ selectors: new List([{
+ type: 'SimpleSelector',
+ sequence: new List([{
+ type: 'Identifier',
+ name: 'x'
+ }])
+ }])
+ },
+ block: block
+ }])
+ };
+}
+
 module.exports = function compress(ast, options) {
  options = options || {};
  ast = ast || { type: 'StyleSheet', rules: new List() };
 
+ if (options.clone) {
+ ast = clone(ast);
+ }
+
  var logger = typeof options.logger === 'function' ? options.logger : Function();
  var specialComments = getCommentsOption(options);
  var restructuring = getRestructureOption(options);
@@ -95,29 +120,11 @@ module.exports = function compress(ast, options) {
  var firstAtrulesAllowed = true;
  var blockNum = 1;
  var blockRules;
- var blockMode = false;
  var usageData = false;
- var info = ast.info || null;
+ var resultAst = ast;
 
  if (ast.type !== 'StyleSheet') {
- blockMode = true;
- ast = {
- type: 'StyleSheet',
- rules: new List([{
- type: 'Ruleset',
- selector: {
- type: 'Selector',
- selectors: new List([{
- type: 'SimpleSelector',
- sequence: new List([{
- type: 'Identifier',
- name: 'x'
- }])
- }])
- },
- block: ast
- }])
- };
+ ast = wrapBlockAst(ast);
  }
 
  if (options.usage) {
@@ -172,21 +179,13 @@ module.exports = function compress(ast, options) {
  result.appendList(blockRules);
  } while (!ast.rules.isEmpty());
 
- if (blockMode) {
- result = !result.isEmpty() ? result.first().block : {
- type: 'Block',
- info: info,
- declarations: new List()
- };
- } else {
- result = {
- type: 'StyleSheet',
- info: info,
- rules: result
- };
+ // resultAst and ast equals for stylesheet nodes
+ // replace rules list in this case
+ if (resultAst === ast) {
+ resultAst.rules = result;
  }
 
  return {
- ast: result
+ ast: resultAst
  };
 };

lib/index.js

@@ -3,6 +3,7 @@ var compress = require('./compressor');
 var translate = require('./utils/translate');
 var translateWithSourceMap = require('./utils/translateWithSourceMap');
 var walkers = require('./utils/walk');
+var clone = require('./utils/clone');
 var List = require('./utils/list');
 
 function debugOutput(name, options, startTime, data) {
@@ -124,5 +125,8 @@ module.exports = {
  // walkers
  walk: walkers.all,
  walkRules: walkers.rules,
- walkRulesRight: walkers.rulesRight
+ walkRulesRight: walkers.rulesRight,
+
+ // utils
+ clone: clone
 };

lib/utils/clone.js

@@ -0,0 +1,23 @@
+var List = require('./list');
+
+module.exports = function clone(node) {
+ var result = {};
+
+ for (var key in node) {
+ var value = node[key];
+
+ if (value) {
+ if (Array.isArray(value)) {
+ value = value.slice(0);
+ } else if (value instanceof List) {
+ value = new List(value.map(clone));
+ } else if (value.constructor === Object) {
+ value = clone(value);
+ }
+ }
+
+ result[key] = value;
+ }
+
+ return result;
+};

test/clone.js

@@ -0,0 +1,46 @@
+var assert = require('assert');
+var csso = require('../lib/index.js');
+
+function sumMarker(ast) {
+ var result = 0;
+
+ csso.walk(ast, function(node) {
+ result += node.marker;
+ });
+
+ return result;
+}
+
+describe('AST clone', function() {
+ it('clone()', function() {
+ var ast = csso.parse('.test{color:red;}@media foo{div{color:green}}');
+ var astCopy = csso.clone(ast);
+
+ csso.walk(ast, function(node) {
+ node.marker = 1;
+ });
+
+ csso.walk(astCopy, function(node) {
+ node.marker = 2;
+ });
+
+ assert(sumMarker(ast) > 1);
+ assert.equal(sumMarker(ast) * 2, sumMarker(astCopy));
+ });
+
+ it('compress(ast, { clone: false })', function() {
+ var ast = csso.parse('.foo{color:red}.bar{color:#ff0000}');
+ var compressedAst = csso.compress(ast, { clone: false }).ast;
+
+ assert.equal(csso.translate(compressedAst), '.bar,.foo{color:red}');
+ assert.equal(csso.translate(ast), '.bar,.foo{color:red}');
+ });
+
+ it('compress(ast, { clone: true })', function() {
+ var ast = csso.parse('.foo{color:red}.bar{color:#ff0000}');
+ var compressedAst = csso.compress(ast, { clone: true }).ast;
+
+ assert.equal(csso.translate(compressedAst), '.bar,.foo{color:red}');
+ assert.equal(csso.translate(ast), '.foo{color:red}.bar{color:#ff0000}');
+ });
+});