Add support for transforms in extensions

Author: wooorm

Diff for: lib/index.js

@@ -36,6 +36,7 @@ function compiler(options) {
   var settings = options || {}
   var config = configure(
     {
+      transforms: [],
       canContainEols: [
         'emphasis',
         'fragment',
@@ -145,7 +146,8 @@ function compiler(options) {
   return compile
 
   function compile(events) {
-    var stack = [{type: 'root', children: []}]
+    var tree = {type: 'root', children: []}
+    var stack = [tree]
     var tokenStack = []
     var listStack = []
     var index = -1
@@ -207,7 +209,7 @@ function compiler(options) {
     }
 
     // Figure out `root` position.
-    stack[0].position = {
+    tree.position = {
       start: point(
         events.length ? events[0][1].start : {line: 1, column: 1, offset: 0}
       ),
@@ -218,7 +220,12 @@ function compiler(options) {
       )
     }
 
-    return stack[0]
+    index = -1
+    while (++index < config.transforms.length) {
+      tree = config.transforms[index](tree) || tree
+    }
+
+    return tree
   }
 
   function prepareList(events, start, length) {
@@ -803,7 +810,7 @@ function extension(config, extension) {
   for (key in extension) {
     left = own.call(config, key) ? config[key] : (config[key] = {})
 
-    if (key === 'canContainEols') {
+    if (key === 'canContainEols' || key === 'transforms') {
       config[key] = [].concat(left, extension[key])
     } else {
       Object.assign(left, extension[key])

Diff for: test/index.js

@@ -123,6 +123,36 @@ test('mdast-util-from-markdown', function (t) {
     this.exit(token)
   }
 
+  t.deepEqual(
+    fromMarkdown('*a*', {
+      mdastExtensions: [{transforms: [transform]}]
+    }).children[0].children,
+    [
+      {
+        type: 'strong',
+        children: [
+          {
+            type: 'text',
+            value: 'a',
+            position: {
+              start: {line: 1, column: 2, offset: 1},
+              end: {line: 1, column: 3, offset: 2}
+            }
+          }
+        ],
+        position: {
+          start: {line: 1, column: 1, offset: 0},
+          end: {line: 1, column: 4, offset: 3}
+        }
+      }
+    ],
+    'should support `transforms` in extensions'
+  )
+
+  function transform(tree) {
+    tree.children[0].children[0].type = 'strong'
+  }
+
   t.throws(
     function () {
       fromMarkdown('a', {