eliminate indentation in error messages

Indented text returned by ‘showMessages’ may be undesirable, but we
cannot add indentation outside of the function (edge case: strings
including newline are displayed in the messages).

Text/Megaparsec/Char.hs

@@ -257,8 +257,8 @@ char c = satisfy (== c) <?> showToken c
 -- 'E'
 -- >>> parseTest (char' 'e') "G"
 -- 1:1:
---   unexpected 'G'
+-- unexpected 'G'
---   expecting 'E' or 'e'
+-- expecting 'E' or 'e'
 
 char' :: MonadParsec s m Char => Char -> m Char
 char' = choice . fmap char . extendi . pure

Text/Megaparsec/Error.hs

@@ -169,12 +169,12 @@ mergeError e1@(ParseError pos1 _) e2@(ParseError pos2 ms2) =
 -- their textual representation.
 
 showMessages :: [Message] -> String
-showMessages [] = "  unknown parse error"
+showMessages [] = "unknown parse error"
 showMessages ms = tail $ foldMap (fromMaybe "") (zipWith f ns rs)
   where (unexpected,    ms') = span ((== 0) . fromEnum) ms
         (expected, messages) = span ((== 1) . fromEnum) ms'
         f prefix m = (prefix ++) <$> m
-        ns = ["\n  unexpected ","\n  expecting ","\n  "]
+        ns = ["\nunexpected ","\nexpecting ","\n"]
         rs = renderMsgs <$> [unexpected, expected, messages]
 
 -- | Render collection of messages. If the collection is empty, return

Text/Megaparsec/Prim.hs

@@ -140,15 +140,15 @@ data Reply s a = Ok a !(State s) | Error ParseError
 --
 -- >>> parseTest (many (char 'r') <* eof) "ra"
 -- 1:2:
---   unexpected 'a'
+-- unexpected 'a'
---   expecting end of input
+-- expecting end of input
 --
 -- We're getting better error messages with help of hints:
 --
 -- >>> parseTest (many (char 'r') <* eof) "ra"
 -- 1:2:
---   unexpected 'a'
+-- unexpected 'a'
---   expecting 'r' or end of input
+-- expecting 'r' or end of input
 
 newtype Hints = Hints [[String]] deriving Monoid
 
@@ -385,8 +385,8 @@ class (A.Alternative m, Monad m, Stream s t)
   --
   -- >>> parseTest (string "let" <|> string "lexical") "lexical"
   -- 1:1:
-  --   unexpected "lex"
+  -- unexpected "lex"
-  --   expecting "let"
+  -- expecting "let"
   --
   -- What happens here? First parser consumes “le” and fails (because it
   -- doesn't see a “t”). The second parser, however, isn't tried, since the
@@ -401,8 +401,8 @@ class (A.Alternative m, Monad m, Stream s t)
   --
   -- >>> parseTest (try (string "let") <|> string "lexical") "le"
   -- 1:1:
-  --   unexpected "le"
+  -- unexpected "le"
-  --   expecting "let" or "lexical"
+  -- expecting "let" or "lexical"
 
   try :: m a -> m a
 

old-tests/Bugs/Bug6.hs

@@ -13,7 +13,7 @@ import Util
 main :: Test
 main =
   testCase "Look-ahead preserving error location (#6)" $
-  parseErrors variable "return" @?= ["  'return' is a reserved keyword"]
+  parseErrors variable "return" @?= ["'return' is a reserved keyword"]
 
 variable :: Parser String
 variable = do

old-tests/Bugs/Bug9.hs

@@ -24,7 +24,7 @@ data Expr = Const Integer | Op Expr Expr deriving Show
 main :: Test
 main =
   testCase "Tracing of current position in error message (#9)"
-  $ result @?= ["  unexpected '>'", "  expecting end of input or operator"]
+  $ result @?= ["unexpected '>'", "expecting end of input or operator"]
   where
     result :: [String]
     result = parseErrors parseTopLevel "4 >> 5"