Handle empty code blocks in Doc2

unison-src/transcripts/fix5349.md

@@ -0,0 +1,21 @@
+```ucm:hide
+scratch/main> builtins.mergeio
+```
+
+Empty code blocks are invalid in Unison, but shouldn’t crash the parser.
+
+````unison:error
+README = {{
+```
+```
+}}
+````
+
+````unison:error
+README = {{ {{ }} }}
+````
+
+
+````unison:error
+README = {{ `` `` }}
+````

unison-src/transcripts/fix5349.output.md

@@ -0,0 +1,78 @@
+Empty code blocks are invalid in Unison, but shouldn’t crash the parser.
+
+```` unison
+README = {{
+```
+```
+}}
+````
+
+``` ucm
+
+  Loading changes detected in scratch.u.
+
+  I expected a block after this (in red), but there wasn't one.  Maybe check your indentation:
+      0 | README = {{
+
+
+```
+``` unison
+README = {{ {{ }} }}
+```
+
+``` ucm
+
+  Loading changes detected in scratch.u.
+
+  I got confused here:
+
+
+
+  I was surprised to find an end of input here.
+  I was expecting one of these instead:
+
+  * bang
+  * do
+  * false
+  * force
+  * handle
+  * if
+  * lambda
+  * let
+  * quote
+  * termLink
+  * true
+  * tuple
+  * typeLink
+
+```
+``` unison
+README = {{ `` `` }}
+```
+
+``` ucm
+
+  Loading changes detected in scratch.u.
+
+  I got confused here:
+
+
+
+  I was surprised to find an end of input here.
+  I was expecting one of these instead:
+
+  * bang
+  * do
+  * false
+  * force
+  * handle
+  * if
+  * lambda
+  * let
+  * quote
+  * termLink
+  * true
+  * tuple
+  * typeLink
+
+```

unison-syntax/src/Unison/Syntax/Lexer/Unison.hs

@@ -77,6 +77,9 @@ data ParsingEnv = ParsingEnv
   }
   deriving (Show)
 
+initialEnv :: BlockName -> ParsingEnv
+initialEnv scope = ParsingEnv [] (Just scope) True
+
 type P = P.ParsecT (Token Err) String (S.State ParsingEnv)
 
 data Err
@@ -196,7 +199,7 @@ token'' tok p = do
     pops p = do
       env <- S.get
       let l = layout env
-      if top l == column p && topContainsVirtualSemis l
+      if column p == top l && topContainsVirtualSemis l
         then pure [Token (Semi True) p p]
         else
           if column p > top l || topHasClosePair l
@@ -289,7 +292,7 @@ lexer scope rem =
       (P.EndOfInput) -> "end of input"
     customErrs es = [Err <$> e | P.ErrorCustom e <- toList es]
     toPos (P.SourcePos _ line col) = Pos (P.unPos line) (P.unPos col)
-    env0 = ParsingEnv [] (Just scope) True
+    env0 = initialEnv scope
 
 -- | hacky postprocessing pass to do some cleanup of stuff that's annoying to
 -- fix without adding more state to the lexer:
@@ -422,15 +425,15 @@ doc2 = do
 
 lexemes' :: P () -> P [Token Lexeme]
 lexemes' eof =
-  -- NB: `postLex` requires the token stream to start with an `Open`, otherwise it can’t create a `T`, so this adds one,
-  --     runs `postLex`, then removes it.
+  -- NB: `postLex` requires the token stream to start with an `Open`, otherwise it can’t create a `BlockTree`, so this
+  --     adds one, runs `postLex`, then removes it.
   fmap (tail . postLex . (Token (Open "fake") mempty mempty :)) $
-    local (\env -> env {inLayout = True, opening = Just "DUMMY"}) do
+    local (const $ initialEnv "DUMMY") do
       p <- lexemes $ [] <$ eof
       -- deals with a final "unclosed" block at the end of `p`)
       unclosed <- takeWhile (("DUMMY" /=) . fst) . layout <$> S.get
-      let pos = end $ last p
-      pure $ p <> replicate (length unclosed) (Token Close pos pos)
+      finalPos <- posP
+      pure $ p <> replicate (length unclosed) (Token Close finalPos finalPos)
 
 -- | Consumes an entire Unison “module”.
 lexemes :: P [Token Lexeme] -> P [Token Lexeme]

unison-syntax/test/Main.hs

@@ -19,7 +19,8 @@ main =
 test :: Test ()
 test =
   scope "lexer" . tests $
-    [ t "1" [Numeric "1"],
+    [ t "" [],
+      t "1" [Numeric "1"],
       t "+1" [Numeric "+1"],
       t "-1" [Numeric "-1"],
       t "-1.0" [Numeric "-1.0"],