Jeff King wrote:
> On Mon, Jul 16, 2018 at 03:03:06PM -0700, Jonathan Nieder wrote:

>> Oh, good point.  In non-daemon mode, we don't let "gc --auto" failure
>> cause the invoking command to fail, but in daemon mode we do.  That
>> should be a straightforward fix; patch coming in a moment.
>
> OK, that definitely sounds like a bug. I'm still confused how that could
> happen, though, since from the caller's perspective they ignore git-gc's
> exit code either way. I guess I'll see in your patch. :)

Alas, I just misremembered.  What I was remembering is that gc --auto
does

        if (auto_gc && too_many_loose_objects())
                warning(_("There are too many unreachable loose objects; "
                        "run 'git prune' to remove them."));
        return 0;

which means that too_many_loose_objects is not an error in undaemonized
mode, while it is in daemonized mode.  But we've already discussed that.

The calling command in the motivating example is Android's "repo" tool:

            bare_git.gc('--auto')

from https://gerrit-review.googlesource.com/c/git-repo/+/10598/.  I
think it's reasonable that it expects a status code of 0 in the normal
case.  So life is less simple than I hoped.

[...]
>> Can you point me to some discussion about building that rate-limiting?
>> The commit message for v2.12.2~17^2 (gc: ignore old gc.log files,
>> 2017-02-10) definitely doesn't describe that as its intent.
>
> I think that commit is a loosening of the rate-limiting (because we'd
> refuse to progress for something that was actually time-based). But the
> original stopping comes from this discussion, I think:
>
>   https://public-inbox.org/git/xmqqlhijznpm....@gitster.dls.corp.google.com/

Interesting!  It looks like that thread anticipated the problems we've
seen here.  Three years without having to have fixed it is a good run,
I suppose.

The discussion of stopping there appears to be primarily about
stopping in the error case, not rate-limiting in the success or
warning case.

Here's a patch for the 'return -1' thing.

-- >8 --
Subject: gc: exit with status 128 on failure

A value of -1 returned from cmd_gc gets propagated to exit(),
resulting in an exit status of 255.  Use die instead for a clearer
error message and a controlled exit.

Signed-off-by: Jonathan Nieder <jrnie...@gmail.com>
---
 builtin/gc.c  | 36 ++++++++++++++++--------------------
 t/t6500-gc.sh |  2 +-
 2 files changed, 17 insertions(+), 21 deletions(-)

diff --git a/builtin/gc.c b/builtin/gc.c
index ccfb1ceaeb..2bebc52bda 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -438,10 +438,10 @@ static const char *lock_repo_for_gc(int force, pid_t* 
ret_pid)
        return NULL;
 }
 
-static int report_last_gc_error(void)
+static void report_last_gc_error(void)
 {
        struct strbuf sb = STRBUF_INIT;
-       int ret = 0;
+       ssize_t ret;
        struct stat st;
        char *gc_log_path = git_pathdup("gc.log");
 
@@ -449,16 +449,17 @@ static int report_last_gc_error(void)
                if (errno == ENOENT)
                        goto done;
 
-               ret = error_errno(_("Can't stat %s"), gc_log_path);
-               goto done;
+               die_errno(_("cannot stat '%s'"), gc_log_path);
        }
 
        if (st.st_mtime < gc_log_expire_time)
                goto done;
 
        ret = strbuf_read_file(&sb, gc_log_path, 0);
+       if (ret < 0)
+               die_errno(_("cannot read '%s'"), gc_log_path);
        if (ret > 0)
-               ret = error(_("The last gc run reported the following. "
+               die(_("The last gc run reported the following. "
                               "Please correct the root cause\n"
                               "and remove %s.\n"
                               "Automatic cleanup will not be performed "
@@ -468,20 +469,18 @@ static int report_last_gc_error(void)
        strbuf_release(&sb);
 done:
        free(gc_log_path);
-       return ret;
 }
 
-static int gc_before_repack(void)
+static void gc_before_repack(void)
 {
        if (pack_refs && run_command_v_opt(pack_refs_cmd.argv, RUN_GIT_CMD))
-               return error(FAILED_RUN, pack_refs_cmd.argv[0]);
+               die(FAILED_RUN, pack_refs_cmd.argv[0]);
 
        if (prune_reflogs && run_command_v_opt(reflog.argv, RUN_GIT_CMD))
-               return error(FAILED_RUN, reflog.argv[0]);
+               die(FAILED_RUN, reflog.argv[0]);
 
        pack_refs = 0;
        prune_reflogs = 0;
-       return 0;
 }
 
 int cmd_gc(int argc, const char **argv, const char *prefix)
@@ -562,13 +561,11 @@ int cmd_gc(int argc, const char **argv, const char 
*prefix)
                        fprintf(stderr, _("See \"git help gc\" for manual 
housekeeping.\n"));
                }
                if (detach_auto) {
-                       if (report_last_gc_error())
-                               return -1;
+                       report_last_gc_error(); /* dies on error */
 
                        if (lock_repo_for_gc(force, &pid))
                                return 0;
-                       if (gc_before_repack())
-                               return -1;
+                       gc_before_repack(); /* dies on failure */
                        delete_tempfile(&pidfile);
 
                        /*
@@ -608,12 +605,11 @@ int cmd_gc(int argc, const char **argv, const char 
*prefix)
                atexit(process_log_file_at_exit);
        }
 
-       if (gc_before_repack())
-               return -1;
+       gc_before_repack();
 
        if (!repository_format_precious_objects) {
                if (run_command_v_opt(repack.argv, RUN_GIT_CMD))
-                       return error(FAILED_RUN, repack.argv[0]);
+                       die(FAILED_RUN, repack.argv[0]);
 
                if (prune_expire) {
                        argv_array_push(&prune, prune_expire);
@@ -623,18 +619,18 @@ int cmd_gc(int argc, const char **argv, const char 
*prefix)
                                argv_array_push(&prune,
                                                "--exclude-promisor-objects");
                        if (run_command_v_opt(prune.argv, RUN_GIT_CMD))
-                               return error(FAILED_RUN, prune.argv[0]);
+                               die(FAILED_RUN, prune.argv[0]);
                }
        }
 
        if (prune_worktrees_expire) {
                argv_array_push(&prune_worktrees, prune_worktrees_expire);
                if (run_command_v_opt(prune_worktrees.argv, RUN_GIT_CMD))
-                       return error(FAILED_RUN, prune_worktrees.argv[0]);
+                       die(FAILED_RUN, prune_worktrees.argv[0]);
        }
 
        if (run_command_v_opt(rerere.argv, RUN_GIT_CMD))
-               return error(FAILED_RUN, rerere.argv[0]);
+               die(FAILED_RUN, rerere.argv[0]);
 
        report_garbage = report_pack_garbage;
        reprepare_packed_git(the_repository);
diff --git a/t/t6500-gc.sh b/t/t6500-gc.sh
index 818435f04e..c474a94a9f 100755
--- a/t/t6500-gc.sh
+++ b/t/t6500-gc.sh
@@ -117,7 +117,7 @@ test_expect_success 'background auto gc does not run if 
gc.log is present and re
        test_config gc.autodetach true &&
        echo fleem >.git/gc.log &&
        test_must_fail git gc --auto 2>err &&
-       test_i18ngrep "^error:" err &&
+       test_i18ngrep "^fatal:" err &&
        test_config gc.logexpiry 5.days &&
        test-tool chmtime =-345600 .git/gc.log &&
        test_must_fail git gc --auto &&
-- 
2.18.0.233.g985f88cf7e

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