Hello everyone! I want to find out the location of the `ghc` (and `ghc-pkg`) executable given the `$libdir` (obtained by `ghc --print-libdir`). Is there a platform independent way of doing that, which we can rely on? E.g. on windows, we found that the ghc executable's location is: * `$libdir/../bin/ghc` For NixOs (or when using ghcup), it works with: * `$libdir/../../bin/ghc` but I worry that this is a just an accident that is not guaranteed by the installation process. I also noticed there seems to be a binary in * `$libdir/bin/ghc` Is one of these ways documented to be guaranteed by the ghc installation process? (P. S. first time using a mailing list, hope I am doing it correctly) Best regards, Fendor
Hi Fendor, On Mon, Feb 08, 2021 at 07:35:12PM +0100, Fendor wrote:
I want to find out the location of the `ghc` (and `ghc-pkg`) executable given the `$libdir` (obtained by `ghc --print-libdir`). Is there a platform independent way of doing that, which we can rely on?
Are you aware of the `ghc --print-libdir` option? I think you'd be much better off going from ghc binary to libdir instead of the other way around. Could you explain why you're trying to do it your way?
(P. S. first time using a mailing list, hope I am doing it correctly)
Seems fine to me :) --Daniel
Hi, Well the purpose is a bit convoluted, but here it goes: Basically, we want to know which `ghc` version `cabal-install` is going to pick for compiling the project in a platform independent way without resorting to linking to `Cabal`. You can execute `cabal exec -- ghc` which launches the correct `ghc` version, but as far as we found out, there is no programmatic way of finding the path to the `ghc` executable itself (`cabal exec -- where ghc` or `cabal exec -- which ghc` fails on windows). What we really want is `cabal-install` to tell us, e.g. with `cabal show-build-info` which is a command not implemented yet[0]. As long as this command is not implemented, we have to monkey patch it in order to satisfy our goals. You can execute `cabal exec -- ghc --print-libdir`, which gives you the `$libdir`, which brings us back to the original question: can we find the `ghc` executable given `$libdir` in a platform independent way? [0] https://github.com/haskell/cabal/pull/6241 Best regards, Fendor On 2/8/21 7:48 PM, Daniel Gröber wrote:
Hi Fendor,
On Mon, Feb 08, 2021 at 07:35:12PM +0100, Fendor wrote:
I want to find out the location of the `ghc` (and `ghc-pkg`) executable given the `$libdir` (obtained by `ghc --print-libdir`). Is there a platform independent way of doing that, which we can rely on? Are you aware of the `ghc --print-libdir` option? I think you'd be much better off going from ghc binary to libdir instead of the other way around.
Could you explain why you're trying to do it your way?
(P. S. first time using a mailing list, hope I am doing it correctly) Seems fine to me :)
--Daniel
Calling `ghc --print-lib-dir` is the only way because the `$libdir` is
actually provided on the cmdline using the -B flag:
https://gitlab.haskell.org/ghc/ghc/-/blob/master/ghc/Main.hs#L110-112
That's why the `ghc` you normally execute is a shell-wrapper around the
`ghc` executable applied to a `-B` argument set at installation time.
But a user is free to move that `$libdir` dir to any other place after
installation and update the `-B` flag accordingly.
On Mon, 8 Feb 2021 at 20:09, Fendor
Hi,
Well the purpose is a bit convoluted, but here it goes:
Basically, we want to know which `ghc` version `cabal-install` is going to pick for compiling the project in a platform independent way without resorting to linking to `Cabal`.
You can execute `cabal exec -- ghc` which launches the correct `ghc` version, but as far as we found out, there is no programmatic way of finding the path to the `ghc` executable itself (`cabal exec -- where ghc` or `cabal exec -- which ghc` fails on windows). What we really want is `cabal-install` to tell us, e.g. with `cabal show-build-info` which is a command not implemented yet[0].
As long as this command is not implemented, we have to monkey patch it in order to satisfy our goals. You can execute `cabal exec -- ghc --print-libdir`, which gives you the `$libdir`, which brings us back to the original question: can we find the `ghc` executable given `$libdir` in a platform independent way?
[0] https://github.com/haskell/cabal/pull/6241
Best regards, Fendor
On 2/8/21 7:48 PM, Daniel Gröber wrote:
Hi Fendor,
On Mon, Feb 08, 2021 at 07:35:12PM +0100, Fendor wrote:
I want to find out the location of the `ghc` (and `ghc-pkg`) executable given the `$libdir` (obtained by `ghc --print-libdir`). Is there a platform independent way of doing that, which we can rely on? Are you aware of the `ghc --print-libdir` option? I think you'd be much better off going from ghc binary to libdir instead of the other way around.
Could you explain why you're trying to do it your way?
(P. S. first time using a mailing list, hope I am doing it correctly) Seems fine to me :)
--Daniel
ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
Hi Fendor, On Mon, Feb 08, 2021 at 08:08:45PM +0100, Fendor wrote:
Basically, we want to know which `ghc` version `cabal-install` is going to pick for compiling the project in a platform independent way without resorting to linking to `Cabal`.
For v2-build this can be found out by looking at plan.json for which you only need to link to cabal-plan (or a json lib of your choice). You do need to have logic run `cabal --dry-run` (IIRC) to generate plan.json if it's not there. I have some code for that in cabal-helper, it's not very tricky as long as you're assuming the cabal project isn't in a broken state anyway.
You can execute `cabal exec -- ghc` which launches the correct `ghc` version, but as far as we found out, there is no programmatic way of finding the path to the `ghc` executable itself (`cabal exec -- where ghc` or `cabal exec -- which ghc` fails on windows).
Seems to me it would be relatively straightforward to add a "which" mode to whatever executable you're shipping (we're talking about hls, right?) so you can do something like: cabal exec -- $path_to_hls which which then just prints the path to GHC on PATH found using the appropriate library function without running into the problem of not having `which` on windows. --Daniel
participants (3)
-
Christiaan Baaij -
Daniel Gröber -
Fendor