resolves #1022 \ as line continuation character in attribute value

- \ as line continuation character in attribute value
- join lines on endline char if preceding line ends with line break sequence
- optimize line continuation parse logic

3 files changed, 38 insertions, 14 deletions

diff --git a/lib/asciidoctor.rb b/lib/asciidoctor.rb
index 729bc7bf..6dc7bc5c 100644
--- a/lib/asciidoctor.rb
+++ b/lib/asciidoctor.rb
@@ -311,10 +311,13 @@ module Asciidoctor
 
   LIST_CONTINUATION = '+'
 
-  # FIXME technically a preceding TAB is allowed too
-  # alternatively, we can enforce everywhere it must be a space
+  # NOTE AsciiDoc Python recognizes both a preceding TAB and a space
   LINE_BREAK = ' +'
 
+  LINE_CONTINUATION = ' \\'
+
+  LINE_CONTINUATION_LEGACY = ' +'
+
   BLOCK_MATH_DELIMITERS = {
     :asciimath => ['\\$', '\\$'],
     :latexmath => ['\\[', '\\]'],
diff --git a/lib/asciidoctor/parser.rb b/lib/asciidoctor/parser.rb
index d2669376..a23998e0 100644
--- a/lib/asciidoctor/parser.rb
+++ b/lib/asciidoctor/parser.rb
@@ -2050,17 +2050,18 @@ class Parser
     match ||= (reader.has_more_lines? ? AttributeEntryRx.match(reader.peek_line) : nil)
     if match
       name = match[1]
-      value = match[2] || ''
-      if value.end_with? LINE_BREAK
-        value = value.chop.rstrip
-        while reader.advance
-          next_line = reader.peek_line.strip
-          break if next_line.empty?
-          if next_line.end_with? LINE_BREAK
-            value = %(#{value} #{next_line.chop.rstrip})
-          else
-            value = %(#{value} #{next_line})
-            break
+      unless (value = match[2] || '').empty?
+        if value.end_with?(line_continuation = LINE_CONTINUATION) ||
+            value.end_with?(line_continuation = LINE_CONTINUATION_LEGACY)
+          value = value.chop.rstrip
+          while reader.advance
+            break if (next_line = reader.peek_line.strip).empty?
+            if (keep_open = next_line.end_with? line_continuation)
+              next_line = next_line.chop.rstrip
+            end
+            separator = (value.end_with? LINE_BREAK) ? EOL : ' '
+            value = %(#{value}#{separator}#{next_line})
+            break unless keep_open
           end
         end
       end
diff --git a/test/attributes_test.rb b/test/attributes_test.rb
index bc2bbf78..52eb0eea 100644
--- a/test/attributes_test.rb
+++ b/test/attributes_test.rb
@@ -16,7 +16,7 @@ context 'Attributes' do
       assert_equal nil, doc.attributes['foo']
     end
 
-    test 'creates an attribute by fusing a multi-line value' do
+    test 'creates an attribute by fusing a legacy multi-line value' do
       str = <<-EOS
 :description: This is the first      +
               Ruby implementation of +
@@ -26,6 +26,26 @@ context 'Attributes' do
       assert_equal 'This is the first Ruby implementation of AsciiDoc.', doc.attributes['description']
     end
 
+    test 'creates an attribute by fusing a multi-line value' do
+      str = <<-EOS
+:description: This is the first \\
+              Ruby implementation of \\
+              AsciiDoc.
+      EOS
+      doc = document_from_string(str)
+      assert_equal 'This is the first Ruby implementation of AsciiDoc.', doc.attributes['description']
+    end
+
+    test 'honors line break characters in multi-line values' do
+      str = <<-EOS
+:signature: Linus Torvalds + \\
+Linux Hacker + \\
+linus.torvalds@example.com
+      EOS
+      doc = document_from_string(str)
+      assert_equal %(Linus Torvalds +\nLinux Hacker +\nlinus.torvalds@example.com), doc.attributes['signature']
+    end
+
     test 'should delete an attribute that ends with !' do
       doc = document_from_string(":frog: Tanglefoot\n:frog!:")
       assert_equal nil, doc.attributes['frog']