Fix 'Ext_lists_without_preceding_blankline' bug.

  * Fixes #1636.
  * Adds a test.

2 files changed, 21 insertions, 2 deletions

diff --git a/src/Text/Pandoc/Readers/Markdown.hs b/src/Text/Pandoc/Readers/Markdown.hs
index 02a787670..239fb4184 100644
--- a/src/Text/Pandoc/Readers/Markdown.hs
+++ b/src/Text/Pandoc/Readers/Markdown.hs
@@ -117,6 +117,12 @@ isBlank _    = False
 -- auxiliary functions
 --
 
+-- | Succeeds when we're in list context.
+inList :: MarkdownParser ()
+inList = do
+  ctx <- stateParserContext <$> getState
+  guard (ctx == ListItemState)
+
 isNull :: F Inlines -> Bool
 isNull ils = B.isNull $ runF ils def
 
@@ -926,6 +932,8 @@ para = try $ do
               <|> (guardEnabled Ext_backtick_code_blocks >> () <$ lookAhead codeBlockFenced)
               <|> (guardDisabled Ext_blank_before_header >> () <$ lookAhead header)
               <|> (guardEnabled Ext_lists_without_preceding_blankline >>
+                       -- Avoid creating a paragraph in a nested list.
+                       notFollowedBy' inList >>
                        () <$ lookAhead listStart)
               <|> do guardEnabled Ext_native_divs
                      inHtmlBlock <- stateInHtmlBlock <$> getState
@@ -1610,8 +1618,7 @@ endline = try $ do
   newline
   notFollowedBy blankline
   -- parse potential list-starts differently if in a list:
-  st <- getState
-  when (stateParserContext st == ListItemState) $ notFollowedBy listStart
+  notFollowedBy (inList >> listStart)
   guardDisabled Ext_lists_without_preceding_blankline <|> notFollowedBy listStart
   guardEnabled Ext_blank_before_blockquote <|> notFollowedBy emailBlockQuoteStart
   guardEnabled Ext_blank_before_header <|> notFollowedBy (char '#') -- atx header
diff --git a/tests/Tests/Readers/Markdown.hs b/tests/Tests/Readers/Markdown.hs
index b45d94032..a7e322306 100644
--- a/tests/Tests/Readers/Markdown.hs
+++ b/tests/Tests/Readers/Markdown.hs
@@ -20,6 +20,9 @@ markdownCDL :: String -> Pandoc
 markdownCDL = readMarkdown def { readerExtensions = Set.insert
                  Ext_compact_definition_lists $ readerExtensions def }
 
+markdownGH :: String -> Pandoc
+markdownGH = readMarkdown def { readerExtensions = githubMarkdownExtensions }
+
 infix 4 =:
 (=:) :: ToString c
      => String -> (String, c) -> Test
@@ -271,5 +274,14 @@ tests = [ testGroup "inline code"
                               plain (text "if this button exists") <>
                               rawBlock "html" "</button>" <>
                               divWith nullAttr (para $ text "with this div too.")]
+          , test markdownGH "issue #1636" $
+              unlines [ "* a"
+                      , "* b"
+                      , "* c"
+                      , "    * d" ]
+              =?>
+              bulletList [ plain "a"
+                         , plain "b"
+                         , plain "c" <> bulletList [plain "d"] ]
           ]
         ]