Allow nested block comments (#2075)

- Closes #2070

src/Juvix/Parser/Lexer.hs

@@ -91,10 +91,21 @@ space' special =
             special
             (notFollowedBy (P.chunk Str.pragmasStart))
           (_commentText, _commentInterval) <- interval $ do
-            void (P.chunk "{-")
-            pack <$> P.manyTill anySingle (P.chunk "-}")
+            void start
+            go 1 ""
           hspace_
           return Comment {..}
+          where
+            start :: m Text = P.chunk "{-"
+            ending :: m Text = P.chunk "-}"
+            go :: Int -> Text -> m Text
+            go n acc = do
+              (txt, startOrEnd) <- P.manyTill_ anySingle (Left <$> start <|> Right <$> ending)
+              case startOrEnd of
+                Left st -> go (n + 1) (acc <> pack txt <> st)
+                Right en
+                  | n > 1 -> go (n - 1) (acc <> pack txt <> en)
+                  | otherwise -> return (acc <> pack txt)
 
 integer' :: ParsecS r (Integer, Interval) -> ParsecS r (Integer, Interval)
 integer' dec = do

tests/Compilation/positive/test003.juvix

@@ -5,7 +5,7 @@ module test003;
 
 Multiline comment
 
-{- nested comments don't work -- }
+{- nested comments work -}
 
 -}
 

tests/Core/positive/test003.jvc

@@ -4,6 +4,6 @@
 
 Multiline comment
 
-{- nested comments don't work -- }
+{- nested comments work -}
 
 -}

tests/positive/Parsing.juvix

@@ -3,5 +3,25 @@ module Parsing;
 let' : Type;
 let' := Type;
 
+{- block comment -}
+-- line comment
+-- line comment 2
+
+{- block comment 2
+
+block comment 2
+-}
+
+{- Nesting
+
+{- Nesting
+
+{- Nesting
+
+-}
+
+-}
+-}
+
 TypeMine : Type;
 TypeMine := Type;