[PATCH v2] run-command: report exec failure

[Junio C Hamano <gitster@pobox.com>]

In 321fd823 ("run-command: mark path lookup errors with ENOENT",
2018-10-24), we rewrote the logic to execute a command by looking
in the directories on $PATH; as a side effect, a request to run a
command that is not found on $PATH is noticed even before a child
process is forked to execute it.

We however stopped to report an exec failure in such a case by
mistake.  Add a logic to report the error unless silent-exec-failure
is requested, to match the original code.

Reported-by: John Passaro <john.a.passaro@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---

 * This time, tests look for the command name in the message, to
   avoid getting affected by the differences the error is reported
   by two codepaths (Windows codepath uses "spawn" while others say
   "run"), which was pointed out by Dscho.

   I am taking that https://travis-ci.org/git/git/jobs/466908193
   that succeeded on Windows as a sign that this is now OK there.

 run-command.c          | 2 ++
 t/t0061-run-command.sh | 9 ++++++---
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/run-command.c b/run-command.c
index d679cc267c..e2bc18a083 100644
--- a/run-command.c
+++ b/run-command.c
@@ -728,6 +728,8 @@ int start_command(struct child_process *cmd)
 	if (prepare_cmd(&argv, cmd) < 0) {
 		failed_errno = errno;
 		cmd->pid = -1;
+		if (!cmd->silent_exec_failure)
+			error_errno("cannot run %s", cmd->argv[0]);
 		goto end_of_spawn;
 	}
 
diff --git a/t/t0061-run-command.sh b/t/t0061-run-command.sh
index b9cfc03a53..8a484878ec 100755
--- a/t/t0061-run-command.sh
+++ b/t/t0061-run-command.sh
@@ -14,11 +14,13 @@ EOF
 >empty
 
 test_expect_success 'start_command reports ENOENT (slash)' '
-	test-tool run-command start-command-ENOENT ./does-not-exist
+	test-tool run-command start-command-ENOENT ./does-not-exist 2>err &&
+	test_i18ngrep "\./does-not-exist" err
 '
 
 test_expect_success 'start_command reports ENOENT (no slash)' '
-	test-tool run-command start-command-ENOENT does-not-exist
+	test-tool run-command start-command-ENOENT does-not-exist 2>err &&
+	test_i18ngrep "does-not-exist" err
 '
 
 test_expect_success 'run_command can run a command' '
@@ -34,7 +36,8 @@ test_expect_success 'run_command is restricted to PATH' '
 	write_script should-not-run <<-\EOF &&
 	echo yikes
 	EOF
-	test_must_fail test-tool run-command run-command should-not-run
+	test_must_fail test-tool run-command run-command should-not-run 2>err &&
+	test_i18ngrep "should-not-run" err
 '
 
 test_expect_success !MINGW 'run_command can run a script without a #! line' '
-- 
2.20.0