This makes the build impure and also causes the contents of a file
outside of the build directory to be overwritten.
The check in `BuildPlan.execute_local` is also expanded to cover
the possibility of an absolute path sneaking through.
If it adds to the environment then it ultimately creates the same
kind of problem it was intended to solve--a need to reproduce
the calls to `subprocess` in the code outside. It's not that hard
to merge two dicts, plus much of the time enough you can get by with
having just `PATH` and `AMARANTH_ENV_*` (if even that).
If an override is wanted it can be done easily enough with:
.execute_local(env={**os.environ, "VAR": "VALUE"})
Build scripts are explicitly intended to have overrides that are
done through the use of environment variables, and right now this
would require a very awkward `run_script=False` invocation followed
by copying a bit of code out of the Amaranth codebase, which is
clearly suboptimal.
In some cases, a toolchain might produce shell output that isn't correct
UTF-8. To avoid crashing in such cases, pass errors="replace" to
bytes.decode.
For example, Lattice Diamond uses the Latin-1 encoding for some reason.
This recently broke my setup because the month turned to "März" in a
German locale:
--- Start Time: Fr. M�r 3 20:01:41 2023
