Re: [PATCH v3 4/4] trace.c: be smart about what env to print in trace_run_command()

From: Junio C Hamano <gitster@pobox.com>
Date: Jan 12, 2018, 19:19 UTC
Message-ID: <xmqqlgh2x4tr.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <20180112184546.GA15514@sigill.intra.peff.net>

Jeff King <peff@peff.net> writes:

Show 9 quoted lines

> The actual prep_childenv() code looks like it would always do
> last-one-wins, so we should treat FOO as unset in that final case. But
> that only kicks in on non-Windows.
>
> On Windows we feed cmd->env straight to mingw_spawnvpe().  That ends up
> in make_environment_block(), which looks like it does something similar.
>
> It's too bad the prep code is not shared, since then we could probably
> just ask _it_ which deltas it applied.

Yeah, but that function does a lot more than computing delta.

It's primary point, which comes from ae25394b ("run-command: prepare child environment before forking", 2017-04-19), is to create a full copy of the environment, not just a series of putenv/unsetenv that describes what gets changed, and that is done to avoid any allocation after fork before exec in the child process.

I guess prep_childenv() could take an extra and optional string-list to report what "deltas" it applied to the tracing machinery. I am not sure if that is worth it, though.