commit-graph: drop COMMIT_GRAPH_WRITE_CHECK_OIDS flag

Since 7c5c9b9c57 (commit-graph: error out on invalid commit oids in
'write --stdin-commits', 2019-08-05), the commit-graph builtin dies on
receiving non-commit OIDs as input to '--stdin-commits'.

This behavior can be cumbersome to work around in, say, the case of
piping 'git for-each-ref' to 'git commit-graph write --stdin-commits' if
the caller does not want to cull out non-commits themselves. In this
situation, it would be ideal if 'git commit-graph write' wrote the graph
containing the inputs that did pertain to commits, and silently ignored
the remainder of the input.

Some options have been proposed to the effect of '--[no-]check-oids'
which would allow callers to have the commit-graph builtin do just that.
After some discussion, it is difficult to imagine a caller who wouldn't
want to pass '--no-check-oids', suggesting that we should get rid of the
behavior of complaining about non-commit inputs altogether.

If callers do wish to retain this behavior, they can easily work around
this change by doing the following:

     git for-each-ref --format='%(objectname) %(objecttype) %(*objecttype)' |
     awk '
       !/commit/ { print "not-a-commit:"$1 }
        /commit/ { print $1 }
     ' |
     git commit-graph write --stdin-commits

To make it so that valid OIDs that refer to non-existent objects are
indeed an error after loosening the error handling, perform an extra
lookup to make sure that object indeed exists before sending it to the
commit-graph internals.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 8 insertions, 7 deletions

diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
index 97eb3b7..75455da 100644
--- a/builtin/commit-graph.c
+++ b/builtin/commit-graph.c
@@ -7,6 +7,7 @@
 #include "commit-graph.h"
 #include "object-store.h"
 #include "progress.h"
+#include "tag.h"
 
 static char const * const builtin_commit_graph_usage[] = {
 	N_("git commit-graph verify [--object-dir <objdir>] [--shallow] [--[no-]progress]"),
@@ -142,18 +143,19 @@ static int write_option_parse_split(const struct option *opt, const char *arg,
 static int read_one_commit(struct oidset *commits, struct progress *progress,
 			   const char *hash)
 {
-	struct commit *result;
+	struct object *result;
 	struct object_id oid;
 	const char *end;
 
 	if (parse_oid_hex(hash, &oid, &end))
 		return error(_("unexpected non-hex object ID: %s"), hash);
 
-	result = lookup_commit_reference_gently(the_repository, &oid, 1);
-	if (result)
-		oidset_insert(commits, &result->object.oid);
-	else
-		return error(_("invalid commit object id: %s"), hash);
+	result = deref_tag(the_repository, parse_object(the_repository, &oid),
+			   NULL, 0);
+	if (!result)
+		return error(_("invalid object: %s"), hash);
+	else if (object_as_type(the_repository, result, OBJ_COMMIT, 1))
+		oidset_insert(commits, &result->oid);
 
 	display_progress(progress, oidset_size(commits));
 
@@ -238,7 +240,6 @@ static int graph_write(int argc, const char **argv)
 					   strbuf_detach(&buf, NULL));
 	} else if (opts.stdin_commits) {
 		oidset_init(&commits, 0);
-		flags |= COMMIT_GRAPH_WRITE_CHECK_OIDS;
 		if (opts.progress)
 			progress = start_delayed_progress(
 				_("Collecting commits from input"), 0);