[PATCH v3 3/3] run-command: show prepared command

[Ian Wienand <iwienand@redhat.com>]

This adds a trace point in prepare_cmd, so we can see the actual
command being run without having to resort to strace/code inspection.

e.g. "test = !echo" when run under GIT_TRACE will show:

 $ GIT_TRACE=1 git test hello
 10:58:56.877234 git.c:755               trace: exec: git-test hello
 10:58:56.877382 run-command.c:657       trace: run_command: git-test hello
 10:58:56.878655 run-command.c:657       trace: run_command: echo hello
 10:58:56.878747 run-command.c:437       trace: prepare_cmd: /usr/bin/echo hello
 hello

A "split" alias, e.g. test = "!echo $*" will show the shell wrapping
and appending of "$@".

 $ GIT_TRACE=1 git test hello
 11:00:45.959420 git.c:755               trace: exec: git-test hello
 11:00:45.959737 run-command.c:657       trace: run_command: git-test hello
 11:00:45.961424 run-command.c:657       trace: run_command: 'echo $*' hello
 11:00:45.961528 run-command.c:437       trace: prepare_cmd: /bin/sh -c 'echo $* "$@"' 'echo $*' hello
 hello hello

For example, this can be very helpful when an alias is giving you an
unexpected syntax error that is very difficult figure out from only
the run_command trace point, e.g.

test = "!for i in 1 2 3; do echo $i; done"

will fail if there is an argument given, we can see why from the
output.

 $ GIT_TRACE=1 test hello
 11:02:39.813030 git.c:755               trace: exec: git-test hello
 11:02:39.813233 run-command.c:657       trace: run_command: git-test hello
 11:02:39.814384 run-command.c:657       trace: run_command: 'for i in 1 2 3; do echo $i; done' hello
 11:02:39.814468 run-command.c:437       trace: prepare_cmd: /bin/sh -c 'for i in 1 2 3; do echo $i; done "$@"' 'for i in 1 2 3; do echo $i; done' hello
 for i in 1 2 3; do echo $i; done: -c: line 1: syntax error near unexpected token `"$@"'
 for i in 1 2 3; do echo $i; done: -c: line 1: `for i in 1 2 3; do echo $i; done "$@"'

A test case is added.

Signed-off-by: Ian Wienand <iwienand@redhat.com>
---
 run-command.c    | 1 +
 t/t0014-alias.sh | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/run-command.c b/run-command.c
index 1b821042b4..36b2b2f194 100644
--- a/run-command.c
+++ b/run-command.c
@@ -435,6 +435,7 @@ static int prepare_cmd(struct strvec *out, const struct child_process *cmd)
 		}
 	}
 
+	trace_argv_printf(&out->v[1], "trace: prepare_cmd:");
 	return 0;
 }
 
diff --git a/t/t0014-alias.sh b/t/t0014-alias.sh
index 95568342be..75c8763a6c 100755
--- a/t/t0014-alias.sh
+++ b/t/t0014-alias.sh
@@ -44,4 +44,11 @@ test_expect_success 'run-command formats empty args properly' '
     test_cmp expect actual
 '
 
+test_expect_success 'tracing a shell alias with arguments shows full prepared command' '
+	git config alias.echo "!echo \$*" &&
+	env GIT_TRACE=1 git echo argument 2>output &&
+	cp output /tmp/output &&
+	test_grep "^trace: prepare_cmd: /bin/sh -c '\''echo \$\* \"\$@\"" output
+'
+
 test_done
-- 
2.45.1