Unscoped GHDL environment variable causes ghdl failure

[sigmuha]

OS: Windows 11
vunit-version: 4.7.0, 5.0.0dev6

Issue

In my build system I have a script that calls VUnit, which set up multiple environment variables, like toolchain paths etc. For ghdl it was GHDL. This causes an environment variable override in vunit/sim_if/ghdl.py line 35:

executable = environ.get("GHDL", "ghdl")

This caused the simulation to fail, as the attempted ghdl path was mangled when trying to find the ghdl version:

    output = cls._get_version_output(prefix)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\<project_path>\.venv\Lib\site-packages\vunit\sim_if\ghdl.py", line 135, in _get_version_output
    return subprocess.check_output(temp).decode()
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Program Files\Python312\Lib\subprocess.py", line 466, in check_output
    return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Program Files\Python312\Lib\subprocess.py", line 548, in run
    with Popen(*popenargs, **kwargs) as process:
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Program Files\Python312\Lib\subprocess.py", line 1026, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "C:\Program Files\Python312\Lib\subprocess.py", line 1538, in _execute_child
    hp, ht, pid, tid = _winapi.CreateProcess(executable, args,
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
PermissionError: [WinError 5] Access is denied

Proposed fix

The root issue is that GHDL is an overly generic environment variable. A better name would use a VUNIT_, or similar prefix, and even specifying its purpose like _EXECUTABLE_NAME or similar.

[LarsAsplund]

Changing the name of that environment variable would be a breaking change and since it was introduced in 2018 by the GHDL author himself I fear that it would affect a large number of projects. I think this is something that you will have to adapt to. For example by using GHDL_PREFIX instead. This is what is used by GHDL to point to the toolchain, see https://ghdl-rad.readthedocs.io/en/latest/using/InvokingGHDL.html?highlight=ghdl_prefix#invoking-ghdl. An alternative is to temporarily override the variable in your run script.

[sigmuha]

I see. This also applies for nvc btw.

Maybe a better warning can be printed, if ghdl --version or ghdl --help fails?
This was not an obvious bug and required digging into the source code to figure out. Correct me if I'm wrong, but these environment variable aren't mentioned in the documentation, which would also help.

[LarsAsplund]

I've added a more informative error message in PR #1150. See if that "solves" your problem

[sigmuha]

Looks good! :D Thanks for quick replies.