Fix extra-prog-path propagation in the codebase.

[jasagredo]

Fixes #9519.
Fixes #8391.

This allows finding system executables in:

• cabal exec will find whatever executable
• cabal build when cloning source-repository-packages will find git
• cabal get if invoking git (with -s for example) will work
• cabal run'ed executable inherits the path

In particular this fixes PATH issues when running MinGW cabal in PowerShell.

Paths added are also now logged in info verbosity.

• Patches conform to the coding conventions.
• Any changes that could be relevant to users have been recorded in the changelog.
• The documentation has been updated, if necessary.
• Manual QA notes have been included.
• Tests have been added. (Ask for help if you don’t know how to write them! Ask for an exemption if tests are too complex for too little coverage!)

QA Notes

In a Windows system with MSYS2/MinGW installed, either system-wide or by ghcup.

Running the following in a PowerShell with previous cabal should fail:

PS C:\Users\Javier\code> cabal exec sh
Error: cabal-3.10.2.0.exe: The program 'sh' is required but it could not be
found.

And now it should work:

PS C:\Users\Javier\code> C:\\Users\\Javier\\code\\cabal\\dist-newstyle\\build\\x86_64-windows\\ghc-9.6.3\\cabal-install-3.11.0.0\\x\\cabal\\build\\cabal\\cabal.exe exec sh
sh-5.2$

Also when you have source-repository-package stanzas in your cabal.project, it doesn't work:

PS C:\Users\Javier\code\foo> cabal build
Error: cabal-3.10.2.0.exe: The program 'git' is required but it could not be
found.

And after this PR it does:

PS C:\Users\Javier\code\foo> C:\\Users\\Javier\\code\\cabal\\dist-newstyle\\build\\x86_64-windows\\ghc-9.6.3\\cabal-install-3.11.0.0\\x\\cabal\\build\\cabal\\cabal.exe build
Warning: this is a debug build of cabal-install with assertions enabled.
Cloning into '/c/Users/Javier/code/foo/dist-newstyle/src/quickchec_-904b1af1c882c12e'...
remote: Enumerating objects: 6266, done.
...

cabal get -s used to fail:

PS C:\Users\Javier\code\tasty> cabal get quickcheck-state-machine -s --verbose=3
...
Searching for git in path.
Cannot find git on the path
CallStack (from HasCallStack):
  withMetadata, called at src\\Distribution\\Simple\\Utils.hs:368:14 in Cabal-3.10.2.1-inplace:Distribution.Simple.Utils
Error: cabal-3.10.2.0.exe: The program 'git' is required but it could not be
found.

not anymore:

PS C:\Users\Javier\code\tasty> C:\\Users\\Javier\\code\\cabal\\dist-newstyle\\build\\x86_64-windows\\ghc-9.6.3\\cabal-install-3.11.0.0\\x\\cabal\\build\\cabal\\cabal.exe get quickcheck-state-machine-0.7.0 -s --verbose=3
...
Searching for git in path.
Found git at C:\msys64\usr\bin\git.exe
Running: "C:\msys64\usr\bin\git.exe" "--version"
C:\msys64\usr\bin\git.exe is version 2.43.0

The PATH printed in the verbose mode used to sometimes have \n interleaved, can be seen with cabal get -s ... --verbose=3:

("PATH","C:\\ghcup\\bin,\nC:\\cabal\\bin,\nC:\\msys64\\mingw64\\bin,\nC:\\msys64\\usr\\bin;C:\\Program Files\\...")

not anymore after this change.

[jasagredo]

It does seem I went a bit over the board. cabal get seems to work without this modification and so does compilation of network (which invokes other executables), so maybe the fix I did in those was not really needed.

[jasagredo]

Ah no actually cabal get without this change shows:

("PATH","C:\\ghcup\\bin,\nC:\\cabal\\bin,\nC:\\msys64\\mingw64\\bin,\nC:\\msys64\\usr\\bin;C:\\Program Files\\...")

(notice the \ns). After this change it is ok.

[jasagredo]

And in fact get doesn't always work!

PS C:\Users\Javier\code\tasty> cabal get quickcheck-state-machine -s --verbose=3
...
Searching for git in path.
Cannot find git on the path
CallStack (from HasCallStack):
  withMetadata, called at src\\Distribution\\Simple\\Utils.hs:368:14 in Cabal-3.10.2.1-inplace:Distribution.Simple.Utils
Error: cabal-3.10.2.0.exe: The program 'git' is required but it could not be
found.

versus the new version

PS C:\Users\Javier\code\tasty> C:\\Users\\Javier\\code\\cabal\\dist-newstyle\\build\\x86_64-windows\\ghc-9.6.3\\cabal-install-3.11.0.0\\x\\cabal\\build\\cabal\\cabal.exe get quickcheck-state-machine-0.7.0 -s --verbose=3
...
Searching for git in path.
Found git at C:\msys64\usr\bin\git.exe
Running: "C:\msys64\usr\bin\git.exe" "--version"
C:\msys64\usr\bin\git.exe is version 2.43.0
...

[jasagredo]

Fixed it also for cabal run!

PS C:\Users\Javier\code\auxxx> cat .\app\Main.hs
module Main where

import System.Process

main :: IO ()
main = callCommand "git --version"
PS C:\Users\Javier\code\auxxx> cabal run
'git' is not recognized as an internal or external command,
operable program or batch file.
PS C:\Users\Javier\code\auxxx> C:\\Users\\Javier\\code\\cabal\\dist-newstyle\\build\\x86_64-windows\\ghc-9.6.3\\cabal-install-3.11.0.0\\x\\cabal\\build\\cabal\\cabal.exe run
...
git version 2.43.0

[fendor]

Idea looks good to me, some small nitpicking.

I am going to manually check the change later.

[jasagredo]

I have reworked the solution a bit, in the same spirit as before but more principled. The commit message should give some guidance for the review.

[alt-romes]

Great! Looks good to me.

[jasagredo]

Each command action is its own function, so there is no better way right now to do this I think without breaking many things. So I'd rather leave it as is.

[jasagredo]

@mergify backport 3.10

[mergify]

backport 3.10

✅ Backports have been created

• #9629 Fix extra-prog-path propagation in the codebase. (backport #9527) has been created for branch 3.10 but encountered conflicts