Haskell: skip multi-line type signature

Close #4013.

The original logic extract "thing" in

    thing
	:: App m
	=> Int
	-> m Int

as a function because the parser cannot find : after "thing" in the line.

The test case is taken from #4013 submitted by @robinp.

Signed-off-by: Masatake YAMATO <[email protected]>

Author: masatake

Units/parser-haskell.r/multi-line-type-signature.d/README

@@ -0,0 +1 @@
+Taken from #4013 submitted by Robin Palotai (@robinp).

Units/parser-haskell.r/multi-line-type-signature.d/args.ctags

@@ -0,0 +1 @@
+--sort=no

Units/parser-haskell.r/multi-line-type-signature.d/expected.tags

@@ -0,0 +1,2 @@
+Foo	input.hs	/^module Foo () where$/;"	m
+thing	input.hs	/^thing x = pure x$/;"	f

Units/parser-haskell.r/multi-line-type-signature.d/input.hs

@@ -0,0 +1,9 @@
+module Foo () where
+
+
+thing
+    :: App m
+    => Int
+    -> m Int
+thing x = pure x
+

parsers/haskell.c

@@ -311,6 +311,32 @@ static void findHaskellTags (int is_literate)
 				 strcmp(token, "import") == 0)
 			;
 		else {
+			/*
+			 * "::" can be after [\n][ \t]+
+			 * ------------------------------
+			 * thing
+			 *   :: App m
+			 *   => Int
+			 *   -> m Int
+			 * ------------------------------
+			 * Skip them to find ':'.
+			 */
+			if (arg[0] == '\n' && arg[1] == '\0') {
+				bool indented = false;
+				while (1)
+				{
+					if ((c = getcFromInputFile()) == EOF)
+						return;
+					if (!isspace(c))
+						break;
+					indented = true;
+				}
+				if (indented)
+					arg[0] = c;
+				else
+					ungetcToInputFile(c);
+			}
+
 			if (arg[0] != ':')
 				add_tag(token, K_FUNCTION, name);
 		}