Re: [PATCH v6 3/3] run-command: show prepared command

> This adds a trace point in start_command so we can see the full
> command invocation without having to resort to strace/code inspection.
> For example:
>
>  $ GIT_TRACE=1 git test foo
>  git.c:755               trace: exec: git-test foo
>  run-command.c:657       trace: run_command: git-test foo
>  run-command.c:657       trace: run_command: 'echo $*' foo
>  run-command.c:749       trace: start_command: /bin/sh -c 'echo $* "$@"' 'echo $*' foo
>
> Prior changes have made the documentation around the internals of the
> alias command execution clearer, but I have still found this detailed
> view of the aliased command being run helpful for debugging purposes.
>
> A test case is added.  This simply looks for the trace point output;
> the details change depending on platform -- the important thing is
> that we have a verbose log point, not so much the details of what
> happens on each platform.
>
> Signed-off-by: Ian Wienand <iwienand@redhat.com>
> ---
>  run-command.c    |  3 +++
>  t/t0014-alias.sh | 12 ++++++++++++
>  2 files changed, 15 insertions(+)
>
> diff --git a/run-command.c b/run-command.c
> index 1b821042b4..31b20123d8 100644
> --- a/run-command.c
> +++ b/run-command.c
> @@ -746,6 +746,8 @@ int start_command(struct child_process *cmd)
>  		goto end_of_spawn;
>  	}
>  
> +	trace_argv_printf(&argv.v[1], "trace: start_command:");
> +
>  	if (pipe(notify_pipe))
>  		notify_pipe[0] = notify_pipe[1] = -1;
>  
> @@ -913,6 +915,7 @@ int start_command(struct child_process *cmd)
>  	else if (cmd->use_shell)
>  		cmd->args.v = prepare_shell_cmd(&nargv, sargv);
>  
> +	trace_argv_printf(cmd->args.v, "trace: start_command:");
>  	cmd->pid = mingw_spawnvpe(cmd->args.v[0], cmd->args.v,
>  				  (char**) cmd->env.v,
>  				  cmd->dir, fhin, fhout, fherr);
> diff --git a/t/t0014-alias.sh b/t/t0014-alias.sh
> index 95568342be..634f6d78ef 100755
> --- a/t/t0014-alias.sh
> +++ b/t/t0014-alias.sh
> @@ -44,4 +44,16 @@ test_expect_success 'run-command formats empty args properly' '
>      test_cmp expect actual
>  '
>  
> +test_expect_success 'tracing a shell alias with arguments shows trace of prepared command' '
> +	cat >expect <<-EOF &&
> +	trace: start_command: SHELL -c ${SQ}echo \$* "\$@"${SQ} ${SQ}echo \$*${SQ} arg
> +	EOF
> +	git config alias.echo "!echo \$*" &&
> +	env GIT_TRACE=1 git echo arg 2>output &&
> +	# redact platform differences
> +	cat output &&