Wrong `Conflicting definitions` error

[sir4ur0n]

Hi,

We are considering migrating to HLS for our project, but we surprisingly get some typecheck errors, while Stack compilation works just fine.

The first problem we encounter is about conflicting definitions.

I tried to pull together a minimal reproducing repo: https://github.com/Sir4ur0n/hls-bug-conflicting-definitions

Everything you need (Stack, HLS) is provided by shell.nix (though build may be long), but the bug remains with traditional Stack + HLS installations (tested on a coworker Macbook).

• stack build works fine
• haskell-language-server gives a typecheck error:

File:     /home/sir4ur0n/sandbox/foobar/src/BugHLS.hs
Hidden:   no
Range:    8:0-8:14
Source:   typecheck
Severity: DsError
Message: 
  Conflicting definitions for ‘a_a28B’
  Bound at: /home/sir4ur0n/sandbox/foobar/src/BugHLS.hs:8:1-14
  /home/sir4ur0n/sandbox/foobar/src/BugHLS.hs:8:1-14
Files that failed:
 * /home/sir4ur0n/sandbox/foobar/src/BugHLS.hs

Even more surprising, the 2 paths are exactly the same, even the character ranges.

Note, we use some extensions in this breaking piece of code

This was tested with HLS 8.8.3 as we use Stack snapshot lts-15.15 which relies on GHC 8.8.3.

I suspect this has to do with TemplateHaskell, but AFAIU HLS should support such code.

Thank you for your help!

[sir4ur0n]

I just tested this problem again today, with a more recent version of HLS, and the bug is gone 🤷‍♂️

However we have another, similar issue, but related to type families and type instances... I'll try to reproduce the issue in my side repository first...

[sir4ur0n]

Small progress: my remaining issue seems to be exactly the same as https://github.com/digital-asset/ghcide/issues/641

Should we keep this issue open?

[jneira]

Let's keep it open to track the resolution upstream.

[jneira]

Let's keep it open to track the resolution upstream.

But in a new one with a specific title #210