Unexpected exception on notification, please report!

[aryairani]

hie/ghcide/haskell-language-server noob here, so I apologize for a possibly-low-quality bug report.

I get a bunch of Exception: user error (Pattern match failure in do expression at src/Development/IDE/Core/Shake.hs:157:5-10) (given in the code block below) when I open my Haskell files. Not sure if this is actually related to the "Unexpected exception on notification" message in the issue title, which I also see in the log, but I don't know that it isn't :)

getIdeGlobalExtras :: forall a . IsIdeGlobal a => ShakeExtras -> IO a
getIdeGlobalExtras ShakeExtras{globals} = do
    Just x <- HMap.lookup (typeRep (Proxy :: Proxy a)) <$> readVar globals
    return $ fromDyn x $ error "Serious error, corrupt globals"

The full log is here: https://gist.github.com/aryairani/90410cce8d5c132b9290329f4d326647

I am using the Atom ide-haskell-hie plugin v0.12.0 with the custom hie-wrapper set to haskell-language-server-wrapper.

Keep up the good work!

[ndmitchell]

Oh dear! Sadly, our error message is pretty crap, and doesn't tell us which global is missing, which would be by far the most useful piece of information. I've sent a patch to improve that: haskell/ghcide#598

Does this reproduce reliably? Or is it a one-off after a sequence of edits that you can't reproduce?

[ndmitchell]

I see "Client does not support watched files. Falling back to OS polling" in the logs, and use of Atom. My guess is most testing is done on clients which do support watched files, so that's seems like a possible lead.

[pepeiborra]

I see "Client does not support watched files. Falling back to OS polling" in the logs, and use of Atom. My guess is most testing is done on clients which do support watched files, so that's seems like a possible lead.

That's a good lead indeed. Even more, there's a few DidChangeWatchedFiles notifications for random files a few lines below:

2020-06-01 12:00:14.849609 [ThreadId 7] - <--2--{"result":[],"jsonrpc":"2.0","id":1}
2020-06-01 12:00:19.661629 [ThreadId 5] - ---> {"jsonrpc":"2.0","method":"workspace/didChangeWatchedFiles","params":{"changes":[{"uri":"file:///Users/arya/unison/master/.stack-work/install/x86_64-osx/98c5c320d01fff2fa8b4023e473195d63b1dfd1f146602174ea52fc2c66bab77/8.6.5/pkgdb/easytest-0.1-GHUNtMcGbspKNzFvNGkuQU.conf","type":3},{"uri":"file:///Users/arya/unison/master/.stack-work/install/x86_64-osx/98c5c320d01fff2fa8b4023e473195d63b1dfd1f146602174ea52fc2c66bab77/8.6.5/pkgdb/package.cache28730-0.tmp","type":3},{"uri":"file:///Users/arya/unison/master/.stack-work/stack.sqlite3-journal","type":3},{"uri":"file:///Users/arya/unison/master/.stack-work/install/x86_64-osx/98c5c320d01fff2fa8b4023e473195d63b1dfd1f146602174ea52fc2c66bab77/8.6.5/pkgdb/package.cache","type":1},{"uri":"file:///Users/arya/unison/master/.stack-work/install/x86_64-osx/98c5c320d01fff2fa8b4023e473195d63b1dfd1f146602174ea52fc2c66bab77/8.6.5/pkgdb/package.cache","type":1}]}}

So the problem is obvious: the client is very buggy. It is sending DidChangeWatchedFiles notifications even though it doesn't advertise support for them, and we did not request them.

The GetFileExists rules use a global which gets installed only when the client supports watched files. It is required in modifyFileExists which is called from the DidChangeWatchedFiles notification handler.

We can patch this on our side by registering the global unconditionally, but @aryairani you should probably switch to another plugin/editor combination

[pepeiborra]

I have moved the issue to the ghcide tracker where it belongs, thanks for the report @aryairani