fromJSON and toJSON

lib/fromJSON.d.ts

@@ -0,0 +1,5 @@
+import { JSONHydrator } from './postcss.js'
+
+declare const fromJSON: JSONHydrator
+
+export default fromJSON

lib/fromJSON.js

@@ -0,0 +1,47 @@
+'use strict'
+
+let Declaration = require('./declaration')
+let Comment = require('./comment')
+let AtRule = require('./at-rule')
+let Root = require('./root')
+let Rule = require('./rule')
+let Input = require('./input')
+let PreviousMap = require('./previous-map')
+
+function fromJSON (json) {
+  let defaults = { ...json }
+  if (json.nodes) {
+    defaults.nodes = json.nodes.map(n => fromJSON(n))
+  }
+  if (json.type === 'root') {
+    if (defaults.source) {
+      defaults.source = { ...defaults.source }
+      if (defaults.source.input) {
+        defaults.source.input = {
+          ...defaults.source.input,
+          __proto__: Input.prototype
+        }
+        if (defaults.source.input.map) {
+          defaults.source.input.map = {
+            ...defaults.source.input.map,
+            __proto__: PreviousMap.prototype
+          }
+        }
+      }
+    }
+    return new Root(defaults)
+  } else if (json.type === 'decl') {
+    return new Declaration(defaults)
+  } else if (json.type === 'rule') {
+    return new Rule(defaults)
+  } else if (json.type === 'comment') {
+    return new Comment(defaults)
+  } else if (json.type === 'atrule') {
+    return new AtRule(defaults)
+  } else {
+    throw new Error('Unknown node type: ' + json.type)
+  }
+}
+
+module.exports = fromJSON
+fromJSON.default = fromJSON

lib/input.js

@@ -8,6 +8,8 @@ let terminalHighlight = require('./terminal-highlight')
 let CssSyntaxError = require('./css-syntax-error')
 let PreviousMap = require('./previous-map')
 
+let fromOffsetCache = Symbol('Input fromOffset cache')
+
 class Input {
   constructor (css, opts = {}) {
     if (
@@ -49,42 +51,48 @@ class Input {
   }
 
   fromOffset (offset) {
-    let lines = this.css.split('\n')
-    let lineToIndex = new Array(lines.length)
-    let prevIndex = 0
+    let lastLine, lineToIndex
+    if (this[fromOffsetCache] == null) {
+      let lines = this.css.split('\n')
+      lineToIndex = new Array(lines.length)
+      let prevIndex = 0
+
+      for (let i = 0, l = lines.length; i < l; i++) {
+        lineToIndex[i] = prevIndex
+        prevIndex += lines[i].length + 1
+      }
 
-    for (let i = 0, l = lines.length; i < l; i++) {
-      lineToIndex[i] = prevIndex
-      prevIndex += lines[i].length + 1
+      lastLine = lineToIndex[lineToIndex.length - 1]
+      this[fromOffsetCache] = {
+        lastLine,
+        lineToIndex
+      }
+    } else {
+      ;({ lastLine, lineToIndex } = this[fromOffsetCache])
     }
 
-    let lastLine = lineToIndex[lineToIndex.length - 1]
-
-    this.fromOffset = index => {
-      let min = 0
-      if (index >= lastLine) {
-        min = lineToIndex.length - 1
-      } else {
-        let max = lineToIndex.length - 2
-        let mid
-        while (min < max) {
-          mid = min + ((max - min) >> 1)
-          if (index < lineToIndex[mid]) {
-            max = mid - 1
-          } else if (index >= lineToIndex[mid + 1]) {
-            min = mid + 1
-          } else {
-            min = mid
-            break
-          }
+    let min = 0
+    if (offset >= lastLine) {
+      min = lineToIndex.length - 1
+    } else {
+      let max = lineToIndex.length - 2
+      let mid
+      while (min < max) {
+        mid = min + ((max - min) >> 1)
+        if (offset < lineToIndex[mid]) {
+          max = mid - 1
+        } else if (offset >= lineToIndex[mid + 1]) {
+          min = mid + 1
+        } else {
+          min = mid
+          break
         }
       }
-      return {
-        line: min + 1,
-        col: index - lineToIndex[min] + 1
-      }
     }
-    return this.fromOffset(offset)
+    return {
+      line: min + 1,
+      col: offset - lineToIndex[min] + 1
+    }
   }
 
   error (message, line, column, opts = {}) {
@@ -168,6 +176,22 @@ class Input {
   get from () {
     return this.file || this.id
   }
+
+  toJSON () {
+    let json = {}
+    for (let name of ['hasBOM', 'css', 'file', 'id']) {
+      if (this[name] != null) {
+        json[name] = this[name]
+      }
+    }
+    if (this.map) {
+      json.map = { ...this.map }
+      if (json.map.consumerCache) {
+        json.map.consumerCache = undefined
+      }
+    }
+    return json
+  }
 }
 
 module.exports = Input

lib/node.js

@@ -187,6 +187,11 @@ class Node {
         })
       } else if (typeof value === 'object' && value.toJSON) {
         fixed[name] = value.toJSON()
+      } else if (this.type === 'root' && name === 'source') {
+        fixed[name] = {
+          input: value.input.toJSON(),
+          start: value.start
+        }
       } else {
         fixed[name] = value
       }

lib/postcss.d.ts

@@ -213,6 +213,10 @@ export interface Stringifier {
   (node: AnyNode, builder: Builder): void
 }
 
+export interface JSONHydrator {
+  (data: object): Node
+}
+
 export interface Syntax {
   /**
    * Function to generate AST by string.
@@ -352,6 +356,17 @@ export interface Postcss {
    */
   parse: Parser
 
+  /**
+   * Rehydrate a JSON AST (from Node#toJSON) back into the corresponding node.
+   *
+   * ```js
+   * const json = root.toJSON();
+   * // ...
+   * const rehydrated  = postcss.fromJSON(json);
+   * ```
+   */
+  fromJSON: JSONHydrator
+
   /**
    * Contains the `list` module.
    */
@@ -412,6 +427,7 @@ export interface Postcss {
 
 export const stringify: Stringifier
 export const parse: Parser
+export const fromJSON: JSONHydrator
 
 export const comment: Postcss['comment']
 export const atRule: Postcss['atRule']

lib/postcss.js

@@ -6,6 +6,7 @@ let LazyResult = require('./lazy-result')
 let Container = require('./container')
 let Processor = require('./processor')
 let stringify = require('./stringify')
+let fromJSON = require('./fromJSON')
 let Warning = require('./warning')
 let Comment = require('./comment')
 let AtRule = require('./at-rule')
@@ -62,6 +63,7 @@ postcss.plugin = function plugin (name, initializer) {
 
 postcss.stringify = stringify
 postcss.parse = parse
+postcss.fromJSON = fromJSON
 postcss.list = list
 
 postcss.comment = defaults => new Comment(defaults)

lib/postcss.mjs

@@ -5,6 +5,7 @@ export default postcss
 export const stringify = postcss.stringify
 export const plugin = postcss.plugin
 export const parse = postcss.parse
+export const fromJSON = postcss.fromJSON
 export const list = postcss.list
 
 export const comment = postcss.comment

test/fromJSON.test.ts

@@ -0,0 +1,33 @@
+import v8 from 'v8'
+
+import postcss, { Root } from '../lib/postcss.js'
+
+it('rehydrates a JSON AST', () => {
+  let cssWithMap = postcss().process(
+    '.foo { color: red; font-size: 12pt; } /* abc */ @media (width: 60em) { }',
+    {
+      from: undefined,
+      map: {
+        inline: true
+      },
+      stringifier: postcss.stringify
+    }
+  ).css
+
+  let root = postcss.parse(cssWithMap)
+
+  let json = root.toJSON()
+  let serialized = v8.serialize(json)
+  let deserialized = v8.deserialize(serialized)
+  let rehydrated = postcss.fromJSON(deserialized) as Root
+
+  rehydrated.nodes[0].remove()
+
+  expect(rehydrated.nodes).toHaveLength(3)
+})
+
+it('throws when rehydrating an invalid JSON AST', () => {
+  expect(() => {
+    postcss.fromJSON({ type: 'not-a-node-type' })
+  }).toThrow('Unknown node type: not-a-node-type')
+})