Don't allow backslash + newline to affect block structure.

Note that as a result of this change, the following,
which formerly produced a header with two lines separated
by a line break, will now produce a header followed by a
paragraph:

    # Hi\
    there

This may affect some existing documents that relied on
this undocumented and unintended behavior.

This change makes pandoc more consistent with other
Markdown implementations, and with itself (since the two-space
version of a line break doesn't work inside ATX headers, and
neither version works inside Setext headers).

Closes #3730.

1 files changed, 8 insertions, 3 deletions

diff --git a/src/Text/Pandoc/Readers/Markdown.hs b/src/Text/Pandoc/Readers/Markdown.hs
index 5e966a17e..e1c481311 100644
--- a/src/Text/Pandoc/Readers/Markdown.hs
+++ b/src/Text/Pandoc/Readers/Markdown.hs
@@ -1451,6 +1451,7 @@ inline = choice [ whitespace
                 , autoLink
                 , spanHtml
                 , rawHtmlInline
+                , escapedNewline
                 , escapedChar
                 , rawLaTeXInline'
                 , exampleRef
@@ -1467,16 +1468,20 @@ escapedChar' = try $ do
   (guardEnabled Ext_all_symbols_escapable >> satisfy (not . isAlphaNum))
      <|> (guardEnabled Ext_angle_brackets_escapable >>
             oneOf "\\`*_{}[]()>#+-.!~\"<>")
-     <|> (guardEnabled Ext_escaped_line_breaks >> char '\n')
      <|> oneOf "\\`*_{}[]()>#+-.!~\""
 
+escapedNewline :: PandocMonad m => MarkdownParser m (F Inlines)
+escapedNewline = try $ do
+  guardEnabled Ext_escaped_line_breaks
+  char '\\'
+  lookAhead (char '\n') -- don't consume the newline (see #3730)
+  return $ return B.linebreak
+
 escapedChar :: PandocMonad m => MarkdownParser m (F Inlines)
 escapedChar = do
   result <- escapedChar'
   case result of
        ' '   -> return $ return $ B.str "\160" -- "\ " is a nonbreaking space
-       '\n'  -> guardEnabled Ext_escaped_line_breaks >>
-                return (return B.linebreak)  -- "\[newline]" is a linebreak
        _     -> return $ return $ B.str [result]
 
 ltSign :: PandocMonad m => MarkdownParser m (F Inlines)