Fix to not escape when unneeded in headings

Related to Mavrin/remark-typograf#2.

Author: wooorm

lib/handle/heading.js

@@ -35,7 +35,7 @@ function heading(node, _, context) {
   sequence = repeat('#', rank)
   exit = context.enter('headingAtx')
   subexit = context.enter('phrasing')
-  value = phrasing(node, context, {before: '\n', after: '\n'})
+  value = phrasing(node, context, {before: '# ', after: '\n'})
   value = value ? sequence + ' ' + value : sequence
   if (context.options.closeAtx) {
     value += ' ' + sequence

lib/util/safe.js

@@ -49,7 +49,7 @@ function safe(context, input, config) {
 
   positions.sort(numerical)
 
-  start = config.before ? 1 : 0
+  start = config.before ? config.before.length : 0
   end = value.length - (config.after ? 1 : 0)
   index = -1
   length = positions.length

test.js

@@ -1045,6 +1045,42 @@ test('heading', function (t) {
     'should serialize a with a closing sequence when `closeAtx` (content)'
   )
 
+  t.equal(
+    to({type: 'heading', depth: 2, children: [{type: 'text', value: '# a'}]}),
+    '## # a\n',
+    'should not escape a `#` at the start of phrasing in a heading'
+  )
+
+  t.equal(
+    to({type: 'heading', depth: 2, children: [{type: 'text', value: '1) a'}]}),
+    '## 1) a\n',
+    'should not escape a `1)` at the start of phrasing in a heading'
+  )
+
+  t.equal(
+    to({type: 'heading', depth: 2, children: [{type: 'text', value: '+ a'}]}),
+    '## + a\n',
+    'should not escape a `+` at the start of phrasing in a heading'
+  )
+
+  t.equal(
+    to({type: 'heading', depth: 2, children: [{type: 'text', value: '- a'}]}),
+    '## - a\n',
+    'should not escape a `-` at the start of phrasing in a heading'
+  )
+
+  t.equal(
+    to({type: 'heading', depth: 2, children: [{type: 'text', value: '= a'}]}),
+    '## = a\n',
+    'should not escape a `=` at the start of phrasing in a heading'
+  )
+
+  t.equal(
+    to({type: 'heading', depth: 2, children: [{type: 'text', value: '> a'}]}),
+    '## > a\n',
+    'should not escape a `>` at the start of phrasing in a heading'
+  )
+
   t.end()
 })