"Conflicting family instance declarations" false positive

[dcastro]

I have a "library" component with a module Src with this code:

{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE DataKinds #-}
module Src where

import Data.Singletons (Sing)
import Data.Vinyl.TypeLevel (Nat(..))

data X (n :: Nat)
type instance Sing = X

This compiles fine with GHC 8.8.3+cabal or stack+lts15.7.

When I first start vscode with ghcide, ghcide reports no errors in this file, as expected.

Now, if I do these steps, ghcide will suddenly start reporting an error.

1. start vscode
2. open Src module from the library component and Test module from the test-suite component (this will force ghcide to load both components)
3. switch between the two files a few times, while typing and deleting some gibberish
4. eventually, ghcide will report this error:

Conflicting family instance declarations:
  Sing = X -- Defined at /home/dc/dev/ghcide-tyfam/src/Src.hs:9:15
  Sing = X -- Defined in module Src

Sometimes you may have to repeat step 3 a few times, sometimes it happens on the first try.

I've recorded a short screencast to better illustrate how to reproduce this:
https://drive.google.com/file/d/1z3BkMHuu2NemDUar1GA4C2y1OD9Cgmzk/view?usp=sharing

I've also uploaded the repo I used to reproduce this and to record the screencast:
https://github.com/dcastro/ghcide-tyfam

Things I've noticed:

• I cannot reproduce this with haskell-ide-engine
• I cannot reproduce this if both modules (Src and Test in this case) are part of the same component

I've compiled ghcide against ghc 8.8.3, like so:

stack install --stack-yaml stack883.yaml

where stack883.yaml is:

# resolver: nightly-2020-02-13
resolver: lts-15.7

packages:
- .
extra-deps:
    - haskell-lsp-0.22.0.0
    - haskell-lsp-types-0.22.0.0
    - lsp-test-0.11.0.2
    - ghc-check-0.5.0.1
    - hie-bios-0.5.0
    - extra-1.7.2

nix:
  packages: [zlib]

GHC: 8.8.3
Ghcide: v0.2.0 or master

[dcastro]

Bumped into another similar issue: ghcide always flags an error for the following code, even though cabal/stack+ghc8.8.3 have no trouble compiling it.

-- Removed the `n :: Nat` kind signature
data X n
type instance Sing = X

The error message is slightly different:

Conflicting family instance declarations:
  Sing = X -- Defined at /home/dc/dev/ghcide-tyfam/src/Src.hs:9:15
  Sing = TypeRep -- Defined in module Data.Singletons.TypeRepTYPE

This may or may not be related to the issue described at the top.

[ndmitchell]

My guess is that haskell/ghcide#596 is related, or at least likely to have a similar root cause. This is a much better reproducer though.

[pepeiborra]

Thanks for the repro! I can confirm that it is the same issue as haskell/ghcide#596. Will look into turning the repro into a test and eventually a fix too.

[pepeiborra]

I spoke too soon, it's not haskell/ghcide#596 as I can still reproduce it after disabling the "Suggest new imports" code action provider. I haven't had any success creating a test for it that drops the singleton dependency either.

[sir4ur0n]

I cannot reproduce this with haskell-ide-engine

FYI we reproduce this issue with haskell-language-server, it happens on our current project 😞

[jneira]

Reported again in haskell/ghcide#210 where @istathar has commented:

I think I just ran into this. It wasn't a problem with 0.4.0 but when the vscode extension downloaded 0.5.0 suddenly I'm getting dozens of errors that look like:

Conflicting family instance declarations:
  Token Label = TechniqueToken
    -- Defined at /home/andrew/src/technique-lang/technique/lib/Technique/Formatter.hs:242:8
  Token Label = TechniqueToken
    -- Defined in module Technique.Formatter typecheck

which is clearly spurious. The build outside from the command-line works fine. Is there a way to work around this perchance?

AfC

So it was not present in hls-0.4.0, which used its own branch of ghcide but it is present now, using ghcide master

[istathar]

(I just tried changing from 'haskell-language-server' to the 'ghcide' in vscode's settings, and if that uses a ghcide from PATH then I can report that the one I just built from master to test something else for @jneira also exhibited this problem)

[jneira]

It seems it was present in hls-0.4.0 too

[paolino]

Any workaround for this issue ?

FWIW , as suggested, removing the lib stanza make it disappear
resulting in

executables:
  misc-services:
    main: misc-services.hs
    source-dirs: 
      - src
      - app

which is a different package than before :-/ and also breaks gen-hie badly

[paolino]

If you run ghcide on the command line you get it straight away, is it right?

…

On Thu, 31 Dec 2020, 22:03 Diogo Castro, ***@***.***> wrote: I have a "library" component with a module Src with this code: {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE DataKinds #-}module Src where import Data.Singletons (Sing)import Data.Vinyl.TypeLevel (Nat(..)) data X (n :: Nat)type instance Sing = X This compiles fine with GHC 8.8.3+cabal or stack+lts15.7. When I first start vscode with ghcide, ghcide reports no errors in this file, as expected. Now, if I do these steps, ghcide will suddenly start reporting an error. 1. start vscode 2. open Src module from the library component and Test module from the test-suite component (this will force ghcide to load both components) 3. switch between the two files a few times, while typing and deleting some gibberish 4. eventually, ghcide will report this error: Conflicting family instance declarations: Sing = X -- Defined at /home/dc/dev/ghcide-tyfam/src/Src.hs:9:15 Sing = X -- Defined in module Src Sometimes you may have to repeat step 3 a few times, sometimes it happens on the first try. I've recorded a short screencast to better illustrate how to reproduce this: https://drive.google.com/file/d/1z3BkMHuu2NemDUar1GA4C2y1OD9Cgmzk/view?usp=sharing I've also uploaded the repo I used to reproduce this and to record the screencast: https://github.com/dcastro/ghcide-tyfam Things I've noticed: - I cannot reproduce this with haskell-ide-engine - I cannot reproduce this if both modules (Src and Test in this case) are part of the same component I've compiled ghcide against ghc 8.8.3, like so: stack install --stack-yaml stack883.yaml where stack883.yaml is: # resolver: nightly-2020-02-13 resolver: lts-15.7 packages: - . extra-deps: - haskell-lsp-0.22.0.0 - haskell-lsp-types-0.22.0.0 - lsp-test-0.11.0.2 - ghc-check-0.5.0.1 - hie-bios-0.5.0 - extra-1.7.2 nix: packages: [zlib] GHC: 8.8.3 Ghcide: v0.2.0 or master — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#773>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAANYHXO2QJUBXGVBN7DV3LSXTRJHANCNFSM4VPXK7UQ> .