Support formatting over TypeOperators

[plcplc]

Currently, running brittany over the below file:

{-# LANGUAGE TypeOperators #-}
module HsOpTy where

import GHC.TypeLits

type Foo = 
  Int :
  '[]

... results in the below error:

$ brittany HsOpTy.hs 
ERROR: brittany pretty printer returned syntactically invalid result.
ERROR: encountered unknown syntactical constructs:
HsOpTy{} at HsOpTy.hs:(6,3)-(7,5)

Note that when the definition of type Foo is just a single line brittany doesn't seem to mind.

Concretely, this is an issue for me in Servant API type definitions, which can get lengthy.

[eborden]

With --output-on-errors you can see the source of the issue.

$ brittany --output-on-errors < foo.hs
ERROR: brittany pretty printer returned syntactically invalid result.
ERROR: encountered unknown syntactical constructs:
HsOpTy{} at stdin:(7,3)-(8,5)
{-# LANGUAGE TypeOperators #-}
module HsOpTy where

import GHC.TypeLits

type Foo = {- BRITTANY ERROR UNHANDLED SYNTACTICAL CONSTRUCT -}

[eborden]

Looks like there is some in progress work here. https://github.com/lspitzner/brittany/blob/master/src/Language/Haskell/Brittany/Internal/Layouters/Type.hs#L473-L532

[eborden]

FYI, that was reached with the --dump-ast-unknown flag.

brittany --dump-ast-unknown < foo.hs
---- ast ----
A Just (Ann (DP (1,2)) [] [] [] Nothing Nothing)
  HsOpTy
    NoExt
    A Just (Ann (DP (0,0)) [] [] [] Nothing Nothing)
      HsTyVar
        NoExt
        NotPromoted
        A Just (Ann (DP (0,0)) [] [] [((G AnnVal),DP (0,0))] Nothing Nothing)
          Unqual {OccName: Int}
    A Just (Ann (DP (0,1)) [] [] [((G AnnVal),DP (0,0))] Nothing Nothing)
      Exact {abstract:Name}
    A Just (Ann (DP (1,2)) [] [] [((G AnnSimpleQuote),DP (0,0)),((G AnnOpenS),DP (0,0)),((G AnnCloseS),DP (0,0))] Nothing Nothing)
      HsExplicitListTy NoExt Promoted []
ERROR: brittany pretty printer returned syntactically invalid result.
ERROR: encountered unknown syntactical constructs:
HsOpTy{} at stdin:(7,3)-(8,5)
  HsOpTy NoExt (HsTyVar NoExt NotPromoted (Unqual {OccName: Int})) (Exact {abstract:Name}) (HsExplicitListTy NoExt Promoted [])

[eborden]

The main problem seems to be the presence of newlines. briDocByExactInlineOnly is being used, which explodes if newlines exist in the AST. So your code above fails, but this works.

{-# LANGUAGE TypeOperators #-}
module HsOpTy where

import GHC.TypeLits

type Foo = Int : '[]

[eborden]

If you can't omit newlines as a work around, I'd recommend using -- brittany-disable-next-binding to disable formatting on that statement in the meantime.

[eborden]

{-# LANGUAGE TypeOperators #-}
module HsOpTy where

import GHC.TypeLits

-- brittany-disable-next-binding
type Foo = 
  Int :
  '[]

[expipiplus1]

I just bumped into this and made a simple test case. Interestingly moving this comma to the next line is enough to stop this happening :/

-- Works
a :: (a
     ,b + c)

-- Fails with the error mentioned above
a :: (a,
      b + c)

[expipiplus1]

This may be another good fit for https://github.com/lspitzner/brittany/issues/28 (passthrough for unhandled constructs)

[lspitzner]

@expipiplus1 Thanks for the hint! #28 was in fact implemented by now. So on current master, the effect of this not being fully supported yet is much more limited.

[expipiplus1]

Great!

[andys8]

I think I'm experiencing the same issue with servant here.

https://github.com/theam/aws-lambda-haskell-runtime/blob/master/examples/wai-app/src/Lib.hs#L60-L66

[Pitometsu]

Any news related to this issue? Is there any help required? This issue actually blocks from using brittany on production projects and unfortunately forces to switch to ormolu without such a problems, but with an alien formatting style instead.

[tfausak]

I'm closing this in favor of #241, which I think is the same thing.