cabal wrapper uses always global ghc in PATH

[jneira]

• detected when testing ghcide in itself (see https://github.com/digital-asset/ghcide/issues/610)
• although you set the field with-compiler: ghc-8.6.5 in the cabal.project hie-bios was using my default ghc in path (ghc-8.8.3)

PS D:\dev\ws\haskell\ghcide> ghc --version
The Glorious Glasgow Haskell Compilation System, version 8.8.3
PS D:\dev\ws\haskell\ghcide> ghcide --version
ghcide version: 0.2.0 (GHC: 8.6.5) (PATH: D:\bin\ghcide.exe)
PS D:\dev\ws\haskell\ghcide> cat .\cabal.project
packages: .

with-compiler: ghc-8.6.5
PS D:\dev\ws\haskell\ghcide> cabal clean
PS D:\dev\ws\haskell\ghcide> ghcide
ghcide version: 0.2.0 (GHC: 8.6.5) (PATH: D:\bin\ghcide.exe)
Ghcide setup tester in D:\dev\ws\haskell\ghcide.
Report bugs at https://github.com/digital-asset/ghcide/issues

Step 1/4: Finding files to test in D:\dev\ws\haskell\ghcide
Found 63 files

Step 2/4: Looking for hie.yaml files that control setup
Found 3 cradles

Step 3/4: Initializing the IDE

Step 4/4: Type checking the files
[INFO] Consulting the cradle for "D:\\dev\\ws\\haskell\\ghcide\\src\\Development\\IDE\\GHC\\WithDynFlags.hs"
> Resolving dependencies...
> Build profile: -w ghc-8.8.3 -O1
> In order, the following will be built (use -v for more details):
>  - ghcide-0.2.0 (lib) (first run)
> Configuring library for ghcide-0.2.0..
> Preprocessing library for ghcide-0.2.0..
File:     D:\dev\ws\haskell\ghcide\src\Development\IDE\GHC\WithDynFlags.hs
Hidden:   no
Range:    1:0-100001:0
Source:   compiler
Severity: DsError
Message:
  <command line>: cannot satisfy -package-id aeson-1.5.1.0-1e42a0cdbd4b065e4d6f1c804d63f35706230918:
  aeson-1.5.1.0-1e42a0cdbd4b065e4d6f1c804d63f35706230918 is unusable due to missing dependencies:
  attoparsec-0.13.2.4-04e8dfec95c5fe0d96babd7d76d0463f6955b1db base-4.13.0.0
  base-compat-b_-0.11.1-1ae618f5c56712e963c7c424698817f24ad5c97a bytestring-0.10.10.0

• hypothesis:
  • the wrapper is calling "ghc" with no args for all invocations with no --interactive
    https://github.com/mpickering/hie-bios/blob/293baaf793f82f639affe734ebe785ccdcafd40b/wrappers/cabal.hs#L19
  • cabal calls ghc --numeric-version, being "ghc" the programs passed in -w as first option, to know the actual ghc version in use

PS D:\dev\ws\haskell\ghcide> ghc --version
The Glorious Glasgow Haskell Compilation System, version 8.8.3
PS D:\dev\ws\haskell\ghcide> cat .\cabal.project
packages: .

with-compiler: ghc-8.6.5
PS D:\dev\ws\haskell\ghcide> cabal exec ghc -- --version
Resolving dependencies...
The Glorious Glasgow Haskell Compilation System, version 8.6.5
PS D:\dev\ws\haskell\ghcide> cabal exec ghc --with-compiler=ghc-8.8.3 -- --version
Resolving dependencies...
The Glorious Glasgow Haskell Compilation System, version 8.8.3
PS D:\dev\ws\haskell\ghcide>

• so it is ignoring the original ghc used in by hie-bios (ghcPath here )

Possible solutions:

• Use an intermmediate env var (HIE_BIOS_WRAPPER_GHC?) to inform the wrapper about the real ghc
• Pass a new argument to the wrapper --hie-bios-ghc and use it, removing it before calling the real ghc

[jneira]

Another test, using directly the wrapper:

PS D:\dev\ws\haskell\ghcide> cat .\cabal.project
packages: .
with-compiler: ghc-8.6.5
PS D:\dev\ws\haskell\ghcide> cabal exec ghc -- --version
Resolving dependencies...
The Glorious Glasgow Haskell Compilation System, version 8.6.5
PS D:\dev\ws\haskell\ghcide> cabal --with-compiler=C:\Users\atrey\AppData\Local\hie-bios\wrapper-3496bab802428a4b095415cdb49e49be.exe exec ghc -- --version
Resolving dependencies...
The Glorious Glasgow Haskell Compilation System, version 8.8.3

[fendor]

I can confirm the behaviour on linux, too.
The hypothesis seems to be correct!

Possible fixes:

• Find the appropriate GHC version in Cradle.hs (via cabal-install-parsers?) and pass it via an environment variable to the wrapper.
• Wait for cabal show-build-info to land (show-build-info (exe:cabal part plus tests) cabal#6241) since it will fix all our problems.
  • Document why it doesn't work and how to work around it.

Unless a lot of users complain about this issue, I am in favour of the latter, as it will be just a few months and solve the issue for good.
Any work-around will be code cruft very soon.

[jneira]

Fair enough, moreover, cabal action uses global ghc in two points:

• the wrapper
• when compiling the wrapper itself, it usually does not throw any error cause the wrapper is dead simple code but it would throw it if you are using cabal but you dont have ghc in global path (nix?)

[fendor]

I think this issue is related: #148

[jneira]

A nice workaround if you use ghcup was mentioned by @hasufell in irc: open a terminal in the project dir root and do PATH=$(ghcup whereis -d ghc <ghc-ver>):$PATH && code .

[hasufell]

Wait for cabal show-build-info to land (show-build-info (exe:cabal part plus tests) haskell/cabal#6241) since it will fix all our problems.

That was one year ago...

[fendor]

Back then it seemed like a reasonable expectation that it was going to be merged soon

[hasufell]

Back then it seemed like a reasonable expectation that it was going to be merged soon

The dream