Strip leading whitespace (#1270)

Fixes #1267.

dhall/src/Dhall/Parser.hs

@@ -26,6 +26,7 @@ import Dhall.Core
 import Dhall.Src (Src(..))
 import Prelude hiding (const, pi)
 
+import qualified Data.Char
 import qualified Data.Text
 import qualified Text.Megaparsec
 
@@ -89,7 +90,7 @@ exprAndHeaderFromText
     -> Either ParseError (Text, Expr Src Import)
 exprAndHeaderFromText delta text = case result of
     Left errInfo   -> Left (ParseError { unwrap = errInfo, input = text })
-    Right (txt, r) -> Right (Data.Text.dropWhileEnd (/= '\n') txt, r)
+    Right (txt, r) -> Right (stripHeader txt, r)
   where
     parser = do
         (bytes, _) <- Text.Megaparsec.match whitespace
@@ -98,3 +99,5 @@ exprAndHeaderFromText delta text = case result of
         return (bytes, r)
 
     result = Text.Megaparsec.parse (unParser parser) delta text
+
+    stripHeader = Data.Text.dropWhile Data.Char.isSpace . Data.Text.dropWhileEnd (/= '\n')

dhall/tests/Dhall/Test/Format.hs

@@ -51,9 +51,10 @@ formatTest characterSet prefix =
 
         inputText <- Text.IO.readFile inputFile
 
-        expr <- Core.throws (Parser.exprFromText mempty inputText)
+        (header, expr) <- Core.throws (Parser.exprAndHeaderFromText mempty inputText)
 
-        let doc        = Pretty.prettyCharacterSet characterSet  expr
+        let doc        =   Doc.pretty header
+                       <>  Pretty.prettyCharacterSet characterSet expr
         let docStream  = Doc.layoutSmart Pretty.layoutOpts doc
         let actualText = Doc.Render.Text.renderStrict docStream
 

dhall/tests/format/headerA.dhall

@@ -0,0 +1,4 @@
+   
+{- bla -}
+  
+True

dhall/tests/format/headerB.dhall

@@ -0,0 +1,3 @@
+{- bla -}
+  
+True