Fix breaks from occurring where they cannot

Closes GH-17.

Author: wooorm

lib/handle/break.js

@@ -1,5 +1,20 @@
 module.exports = hardBreak
 
-function hardBreak() {
+var patternInScope = require('../util/pattern-in-scope')
+
+function hardBreak(node, _, context, safe) {
+  var index = -1
+
+  while (++index < context.unsafe.length) {
+    // If we can’t put eols in this construct (setext headings, tables), use a
+    // space instead.
+    if (
+      context.unsafe[index].character === '\n' &&
+      patternInScope(context.stack, context.unsafe[index])
+    ) {
+      return /[ \t]/.test(safe.before) ? '' : ' '
+    }
+  }
+
   return '\\\n'
 }

lib/handle/inline-code.js

@@ -1,7 +1,7 @@
 module.exports = inlineCode
 inlineCode.peek = inlineCodePeek
 
-var compilePattern = require('../util/compile-pattern')
+var patternCompile = require('../util/pattern-compile')
 
 function inlineCode(node, parent, context) {
   var value = node.value || ''
@@ -44,7 +44,7 @@ function inlineCode(node, parent, context) {
     // CR.
     if (!pattern.atBreak) continue
 
-    expression = compilePattern(pattern)
+    expression = patternCompile(pattern)
 
     while ((match = expression.exec(value))) {
       position = match.index

lib/util/compile-pattern.js renamed to lib/util/pattern-compile.js

@@ -1,6 +1,6 @@
-module.exports = compilePattern
+module.exports = patternCompile
 
-function compilePattern(pattern) {
+function patternCompile(pattern) {
   var before
   var after
 

lib/util/pattern-in-scope.js

@@ -0,0 +1,30 @@
+module.exports = patternInScope
+
+function patternInScope(stack, pattern) {
+  return (
+    listInScope(stack, pattern.inConstruct, true) &&
+    !listInScope(stack, pattern.notInConstruct)
+  )
+}
+
+function listInScope(stack, list, none) {
+  var index
+
+  if (!list) {
+    return none
+  }
+
+  if (typeof list === 'string') {
+    list = [list]
+  }
+
+  index = -1
+
+  while (++index < list.length) {
+    if (stack.indexOf(list[index]) !== -1) {
+      return true
+    }
+  }
+
+  return false
+}

lib/util/safe.js

@@ -1,6 +1,7 @@
 module.exports = safe
 
-var compilePattern = require('./compile-pattern')
+var patternCompile = require('./pattern-compile')
+var patternInScope = require('./pattern-in-scope')
 
 function safe(context, input, config) {
   var value = (config.before || '') + (input || '') + (config.after || '')
@@ -20,14 +21,11 @@ function safe(context, input, config) {
   while (++index < context.unsafe.length) {
     pattern = context.unsafe[index]
 
-    if (
-      !inScope(context.stack, pattern.inConstruct, true) ||
-      inScope(context.stack, pattern.notInConstruct)
-    ) {
+    if (!patternInScope(context.stack, pattern)) {
       continue
     }
 
-    expression = compilePattern(pattern)
+    expression = patternCompile(pattern)
 
     while ((match = expression.exec(value))) {
       // Often, patterns which depend on a character before or after it, such
@@ -118,28 +116,6 @@ function safe(context, input, config) {
   return result.join('')
 }
 
-function inScope(stack, list, none) {
-  var index
-
-  if (!list) {
-    return none
-  }
-
-  if (typeof list === 'string') {
-    list = [list]
-  }
-
-  index = -1
-
-  while (++index < list.length) {
-    if (stack.indexOf(list[index]) !== -1) {
-      return true
-    }
-  }
-
-  return false
-}
-
 function numerical(a, b) {
   return a - b
 }

test.js

@@ -571,6 +571,24 @@ test('blockquote', function (t) {
 test('break', function (t) {
   t.equal(to({type: 'break'}), '\\\n', 'should support a break')
 
+  t.equal(
+    to(from('a  \nb\n=\n')),
+    '# a b\n',
+    'should serialize breaks in heading (atx) as a space'
+  )
+
+  t.equal(
+    to(from('a \\\nb\n=\n')),
+    '# a b\n',
+    'should serialize breaks in heading (atx) as nothing when preceded by a space'
+  )
+
+  t.equal(
+    to(from('a  \nb\n=\n'), {setext: true}),
+    'a\\\nb\n=\n',
+    'should serialize breaks in heading (setext)'
+  )
+
   t.end()
 })