Fix to not escape superfluous character

If a character is supposed to be escaped, but only because it has a condition
on the next character, and the next character is definitely being escaped),
then leave the first one and defer to the next.

Closes GH-5.

Author: wooorm

lib/util/safe.js

@@ -10,6 +10,8 @@ function safe(context, input, config) {
   var index = -1
   var positions = []
   var result = []
+  var infos = {}
+  var info
   var position
   var character
   var pattern
@@ -36,12 +38,30 @@ function safe(context, input, config) {
       continue
     }
 
-    expression = toExpression(pattern)
+    expression =
+      pattern._compiled || (pattern._compiled = toExpression(pattern))
 
     while ((match = expression.exec(value))) {
-      positions.push(
+      position =
         match.index + (pattern.before || pattern.atBreak ? match[1].length : 0)
-      )
+
+      info = {
+        before: pattern.atBreak || 'before' in pattern,
+        after: 'after' in pattern
+      }
+
+      if (positions.indexOf(position) === -1) {
+        positions.push(position)
+        infos[position] = info
+      } else {
+        if (infos[position].before && !info.before) {
+          infos[position].before = false
+        }
+
+        if (infos[position].after && !info.after) {
+          infos[position].after = false
+        }
+      }
     }
   }
 
@@ -54,22 +74,35 @@ function safe(context, input, config) {
 
   while (++index < length) {
     position = positions[index]
+    info = infos[position]
 
     if (
       // Character before or after matched:
       position < start ||
-      position >= end ||
-      // Character matched multiple times:
-      position === positions[index + 1]
+      position >= end
+    ) {
+      continue
+    }
+
+    // If this character is supposed to be escaped, but only because it has a
+    // condition on the next character, and the next character is definitly
+    // being escaped), then skip this escape.
+    if (
+      info.after &&
+      position + 1 < end &&
+      positions[index + 1] === position + 1 &&
+      !infos[position + 1].before &&
+      !infos[position + 1].after
     ) {
       continue
     }
 
+    character = value.charAt(position)
+
     if (start !== position) {
       result.push(value.slice(start, position))
     }
 
-    character = value.charAt(position)
     start = position
 
     if (

package.json

@@ -80,6 +80,7 @@
     "prettier": true,
     "esnext": false,
     "rules": {
+      "complexity": "off",
       "unicorn/prefer-includes": "off"
     },
     "ignores": [

test.js

@@ -2472,13 +2472,13 @@ test('escape', function (t) {
 
   t.equal(
     to({type: 'paragraph', children: [{type: 'text', value: '![a][b]'}]}),
-    '\\!\\[a]\\[b]\n',
+    '!\\[a]\\[b]\n',
     'should escape what would otherwise be an image (reference)'
   )
 
   t.equal(
     to({type: 'paragraph', children: [{type: 'text', value: '![](a.jpg)'}]}),
-    '\\!\\[]\\(a.jpg)\n',
+    '!\\[]\\(a.jpg)\n',
     'should escape what would otherwise be an image (resource)'
   )