Brittany is not initialised with stack default extensions

[santiweight]

I am unsure whether this is a feature request or a bug...

VS Code - haskell extension

Bug repro

https://github.com/santiweight/hls-bug-brittany

See the diff for the most recent commit

Contents of hie.yaml:

cradle:
  stack:
    component: "hls-bug-brittany:lib"

Steps to reproduce

Have a syntactic extension (e.g. PatternSynonyms) in package.yaml's default extensions and then pretty print using Brittany.

Expected behaviour

Pretty printing should occur

Actual behaviour

Error prints:

santiweight/hls-bug-brittany/src/Lib.hs
2020-12-11 18:27:42.718845 [ThreadId 5982] - Plugin ModuleName  prefix Just "/Users/santiweight/hls-bug-brittany/src"
2020-12-11 18:27:42.718885 [ThreadId 5982] - Plugin ModuleName  mdlName Just "Lib"
2020-12-11 18:27:42.718989 [ThreadId 5991] - finish: ModuleName.GetParsedModule (took 0.00s)
2020-12-11 18:27:42.719014 [ThreadId 5982] - Plugin ModuleName  correct Just "Lib" stated Just (Range {_start = Position {_line = 0, _character = 7}, _end = Position {_line = 0, _character = 10}},"Lib")
2020-12-11 18:27:42.71907 [ThreadId 5982] - Plugin ModuleName  actions []
2020-12-11 18:27:42.719291 [ThreadId 7] - <--2--{"result":[],"jsonrpc":"2.0","id":127}
2020-12-11 18:27:43.886555 [ThreadId 5] - ---> {"jsonrpc":"2.0","id":128,"method":"textDocument/formatting","params":{"textDocument":{"uri":"file:///Users/santiweight/hls-bug-brittany/src/Lib.hs"},"options":{"tabSize":4,"insertSpaces":true}}}
2020-12-11 18:27:43.886895 [ThreadId 5997] - finish: Formatter (took 0.00s)
2020-12-11 18:27:43.886922 [ThreadId 5996] - Formatter.doFormatting: contents="module Lib\n    ( someFunc\n    ) where\n\nsomeFunc :: IO ()\nsomeFunc = putStrLn \"someFunc\"\n\nnewtype Bar a = Bar a\n\npattern Foo :: Int -> Bar Int\npattern Foo a = Bar a\n\n"
[Error - 6:27:43 PM] Request textDocument/formatting failed.
  Message: brittanyCmd: stdin:10:1-11: Invalid type signature: pattern Foo :: ...
Perhaps you meant to use PatternSynonyms?

  Code: -32602
2020-12-11 18:27:43.89336 [ThreadId 7] - <--2--{"error":{"code":-32602,"message":"brittanyCmd: stdin:10:1-11: Invalid type signature: pattern Foo :: ...\nPerhaps you meant to use PatternSynonyms?\n"},"jsonrpc":"2.0","id":128}

[Ailrun]

Is {- # LANGUAGE PatternSynonyms #-} correct pragma?
I think that's invalid...

[santiweight]

This was simply so you can enable/disable easily - it's a comment until you remove the whitespace

[santiweight]

The point being that since the extension was inactive (the pragma was commented out), the bug arose

[Ailrun]

I mean, does normal brittany command work when you don't have the pragma (even though your file contains pattern synonym)? I think it doesn't...

[Ailrun]

Sorry, I have misread the issue. So the problem is that Brittany does not recognize the extension in package.yaml, right?
Then I would say this one is more like an enhancement than a bug, as the original Brittany command also requires an extra config file with an extension list to apply them by default.

[santiweight]

@Ailrun I believe this to be the case. I'm not aware whether hls picks up the config in package.yaml. If so, this might not be such a hard enhancement. I can always take a look if someone is willing to point me somewhere in the code :)

[jneira]

Afaik this should be closed by #1362, @santiweight could you confirm brittany honours stack default extensions?