Add an :incorrect transcript tag

This is basically the opposite of `:failure` – it indicates that a
successful result is incorrect. The correct result may either be an
error (which will be caught by the transcript runner) or a different
result then what is currently expected (which won’t be caught by the
runner, but the appearance of `:incorrect` conveys to the programmer
that the output.md diff may be an improvement from the previous state).

unison-cli/src/Unison/Codebase/Transcript.hs

@@ -19,7 +19,7 @@ import Unison.Core.Project (ProjectBranchName, ProjectName)
 import Unison.Prelude
 import Unison.Project (ProjectAndBranch)
 
-data Result = Success | Error | Failure
+data Result = Success | Incorrect | Error | Failure
 
 type ScratchFileName = Text
 

unison-cli/src/Unison/Codebase/Transcript/Parser.hs

@@ -146,6 +146,7 @@ expectingError :: P Result
 expectingError =
   (Error <$ word ":error")
     <|> (Failure <$ word ":failure")
+    <|> (Incorrect <$ word ":incorrect")
     <|> pure Success
 
 untilSpace1 :: P Text

unison-cli/src/Unison/Codebase/Transcript/Runner.hs

@@ -266,6 +266,14 @@ run isTest verbosity dir stanzas codebase runtime sbRuntime nRuntime ucmVersion
                             liftIO $ writeIORef hasErrors True
                             liftIO (readIORef allowErrors) >>= \case
                               Success -> liftIO . dieWithMsg $ Pretty.toPlain terminalWidth msg
+                              Incorrect ->
+                                liftIO . dieWithMsg . Pretty.toPlain terminalWidth $
+                                  "The stanza above previously had an incorrect successful result, but now fails with"
+                                    <> "\n"
+                                    <> Pretty.border 2 msg
+                                    <> "\n"
+                                    <> "if this is the expected result, replace `:incorrect` with `:error`, otherwise "
+                                    <> "change `:incorrect` to `:failure`."
                               _ -> do
                                 liftIO . output . Pretty.toPlain terminalWidth $ "\n" <> msg <> "\n"
                                 awaitInput
@@ -366,6 +374,7 @@ run isTest verbosity dir stanzas codebase runtime sbRuntime nRuntime ucmVersion
         output rendered
         when (Output.isFailure o) case errOk of
           Success -> dieWithMsg rendered
+          Incorrect -> dieWithMsg rendered
           _ -> writeIORef hasErrors True
 
       printNumbered :: Output.NumberedOutput -> IO Output.NumberedArgs
@@ -376,6 +385,7 @@ run isTest verbosity dir stanzas codebase runtime sbRuntime nRuntime ucmVersion
         output rendered
         when (Output.isNumberedFailure o) case errOk of
           Success -> dieWithMsg rendered
+          Incorrect -> dieWithMsg rendered
           _ -> writeIORef hasErrors True
         pure numberedArgs