BUG: Parsect PackageIdentifier is broken

If we try to parse <flavour>-<version>-<pkg>-<version> for e.g. <pkg>-<version> this will break in
-- | Parse the @setup-config@ file header, returning the package identifiers
-- for Cabal and the compiler.
parseHeader
  :: ByteString
  -- ^ The file contents.
  -> IO (PackageIdentifier, PackageIdentifier)

  The issue is that we I guess parse e.g. Cabal-x.y.z as compiler flavour + version, and then have nothing for the PackageIdentifier to parse. This code needs to be fixed properly to try and parse compier-version-pkg-version or only pkg-version (and set compiler to Nothing).

Author: angerman

Cabal-syntax/src/Distribution/Types/PackageId.hs

@@ -64,13 +64,13 @@ instance Pretty PackageIdentifier where
 -- Nothing
 instance Parsec PackageIdentifier where
   parsec = do
-    comp <- parsec <* P.char '-'
+    -- comp <- parsec <* P.char '-'
     xs' <- P.sepByNonEmpty component (P.char '-')
     (v, xs) <- case simpleParsec (NE.last xs') of
       Nothing -> return (nullVersion, toList xs') -- all components are version
       Just v -> return (v, NE.init xs')
     if not (null xs) && all (\c -> all (/= '.') c && not (all isDigit c)) xs
-      then return $ PackageIdentifier (mkPackageName (intercalate "-" xs)) v comp
+      then return $ PackageIdentifier (mkPackageName (intercalate "-" xs)) v Nothing
       else fail "all digits or a dot in a portion of package name"
     where
       component = P.munch1 (\c -> isAlphaNum c || c == '.')