Strip a single leading space from bird tracks (#201)

This makes bird tracks in the form

> foo
> bar
> bat

parse as if they had been written as

>foo
>bar
>bat

ie. without the leading whitespace in front of every line.

Ideally we also want to look into how leading whitespace affects code
blocks written using the @ @ syntax, which are currently unaffected by
this patch.

1 files changed, 10 insertions, 1 deletions

diff --git a/src/Haddock/Parser.hs b/src/Haddock/Parser.hs
index e9bed2a5..a6ad817c 100644
--- a/src/Haddock/Parser.hs
+++ b/src/Haddock/Parser.hs
@@ -302,10 +302,19 @@ takeNonEmptyLine = do
     (++ "\n") . decodeUtf8 <$> (takeWhile1 (/= '\n') >>= nonSpace) <* "\n"
 
 birdtracks :: Parser (Doc a)
-birdtracks = DocCodeBlock . DocString . intercalate "\n" <$> many1 line
+birdtracks = DocCodeBlock . DocString . intercalate "\n" . stripSpace <$> many1 line
   where
     line = skipHorizontalSpace *> ">" *> takeLine
 
+-- | Strip leading spaces, but ignore blank lines. If any of the lines don't
+--   start with a ' ', however, we don't touch the block.
+stripSpace :: [String] -> [String]
+stripSpace = fromMaybe <*> mapM strip
+  where
+    strip (' ':xs) = Just xs
+    strip "" = Just ""
+    strip _  = Nothing
+
 -- | Parses examples. Examples are a paragraph level entitity (separated by an empty line).
 -- Consecutive examples are accepted.
 examples :: Parser (Doc a)