Improve source excerpt highlighting

unison-src/transcripts/error-messages.output.md

@@ -215,7 +215,7 @@ foo = match 1 with
       3 | 
   
   I was surprised to find an end of section here.
-  I was hoping for one of these instead:
+  I was expecting one of these instead:
   
   * ","
   * case match
@@ -261,7 +261,7 @@ x = match Some a with
       7 | 
   
   I was surprised to find an end of section here.
-  I was hoping for one of these instead:
+  I was expecting one of these instead:
   
   * ","
   * blank
@@ -289,7 +289,7 @@ x = match Some a with
   
   
   I was surprised to find a -> here.
-  I was hoping for one of these instead:
+  I was expecting one of these instead:
   
   * newline or semicolon
 
@@ -311,7 +311,7 @@ x = match Some a with
   
   
   I was surprised to find a '|' here.
-  I was hoping for one of these instead:
+  I was expecting one of these instead:
   
   * newline or semicolon
 

unison-src/transcripts/generic-parse-errors.output.md

@@ -15,7 +15,7 @@ x =
   
   
   I was surprised to find a 1 here.
-  I was hoping for one of these instead:
+  I was expecting one of these instead:
   
   * end of input
   * hash (ex: #af3sj3)
@@ -79,7 +79,7 @@ x = "hi
       2 | 
   
   I was surprised to find an end of input here.
-  I was hoping for one of these instead:
+  I was expecting one of these instead:
   
   * "
   * \s
@@ -99,7 +99,7 @@ y : a
       2 | 
   
   I was surprised to find an end of section here.
-  I was hoping for one of these instead:
+  I was expecting one of these instead:
   
   * ->
   * newline or semicolon

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

@@ -278,12 +278,20 @@ lexer0' scope rem =
                       & fmap errorItemToString
                       & maybeToList
                       & Set.fromList
+                  errorLength :: Int
+                  errorLength = case Set.toList unexpectedStr of
+                    [] -> 0
+                    (x : _) -> length x
                   expectedStr :: Set String
                   expectedStr =
                     expectedTokens
                       & Set.map errorItemToString
                   err = UnexpectedTokens $ formatTrivialError unexpectedStr expectedStr
-               in [Token (Err err) (toPos top) (toPos top)]
+                  startPos = toPos top
+                  -- This is just an attempt to highlight errors better in source excerpts.
+                  -- It may not work in all cases, but should generally provide a better experience.
+                  endPos = startPos & \(Pos l c) -> Pos l (c + errorLength)
+               in [Token (Err err) startPos endPos]
        in errsWithSourcePos >>= errorToTokens
     Right ts -> Token (Open scope) topLeftCorner topLeftCorner : tweak ts
   where
@@ -330,7 +338,7 @@ formatTrivialError unexpectedTokens expectedTokens =
         xs -> "I was surprised to find these:\n\n* " <> List.intercalate "\n* " xs
       expectedMsg = case Set.toList expectedTokens of
         [] -> Nothing
-        xs -> Just $ "\nI was hoping for one of these instead:\n\n* " <> List.intercalate "\n* " xs
+        xs -> Just $ "\nI was expecting one of these instead:\n\n* " <> List.intercalate "\n* " xs
    in concat $ catMaybes [Just unexpectedMsg, expectedMsg]
 
 displayLexeme :: Lexeme -> String