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

[Ian Wienand <iwienand@redhat.com>]

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 &&
+	sed -n -e "s/^\(trace: start_command:\) .* -c /\1 SHELL -c /p" output >actual &&
+	test_cmp expect actual
+'
+
 test_done
-- 
2.45.1