[PATCH v3 8/8] commit-graph: drop COMMIT_GRAPH_WRITE_CHECK_OIDS flag

[Taylor Blau <me@ttaylorr.com>]

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>
---
 Documentation/git-commit-graph.txt |  6 ++++--
 builtin/commit-graph.c             | 15 ++++++++-------
 commit-graph.c                     |  2 --
 commit-graph.h                     |  4 +---
 t/t5318-commit-graph.sh            | 15 +++++++++++----
 5 files changed, 24 insertions(+), 18 deletions(-)

diff --git a/Documentation/git-commit-graph.txt b/Documentation/git-commit-graph.txt
index 53a650225a..fcac7d12e1 100644
--- a/Documentation/git-commit-graph.txt
+++ b/Documentation/git-commit-graph.txt
@@ -47,8 +47,10 @@ with `--stdin-commits` or `--reachable`.)
 +
 With the `--stdin-commits` option, generate the new commit graph by
 walking commits starting at the commits specified in stdin as a list
-of OIDs in hex, one OID per line. (Cannot be combined with
-`--stdin-packs` or `--reachable`.)
+of OIDs in hex, one OID per line. OIDs that resolve to non-commits
+(either directly, or by peeling tags) are silently ignored. OIDs that
+are malformed, or do not exist generate an error. (Cannot be combined
+with `--stdin-packs` or `--reachable`.)
 +
 With the `--reachable` option, generate the new commit graph by walking
 commits starting at all refs. (Cannot be combined with `--stdin-commits`
diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
index 83c55d9227..d3bd1c31c9 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));
 
@@ -240,7 +242,6 @@ 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);
diff --git a/commit-graph.c b/commit-graph.c
index 3ea70e6676..2ff042fbf4 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -881,7 +881,6 @@ struct write_commit_graph_context {
 	unsigned append:1,
 		 report_progress:1,
 		 split:1,
-		 check_oids:1,
 		 changed_paths:1,
 		 order_by_pack:1;
 
@@ -2011,7 +2010,6 @@ int write_commit_graph(struct object_directory *odb,
 	ctx->append = flags & COMMIT_GRAPH_WRITE_APPEND ? 1 : 0;
 	ctx->report_progress = flags & COMMIT_GRAPH_WRITE_PROGRESS ? 1 : 0;
 	ctx->split = flags & COMMIT_GRAPH_WRITE_SPLIT ? 1 : 0;
-	ctx->check_oids = flags & COMMIT_GRAPH_WRITE_CHECK_OIDS ? 1 : 0;
 	ctx->split_opts = split_opts;
 	ctx->changed_paths = flags & COMMIT_GRAPH_WRITE_BLOOM_FILTERS ? 1 : 0;
 	ctx->total_bloom_filter_data_size = 0;
diff --git a/commit-graph.h b/commit-graph.h
index 4212766a4f..3ba0da1e5f 100644
--- a/commit-graph.h
+++ b/commit-graph.h
@@ -91,9 +91,7 @@ enum commit_graph_write_flags {
 	COMMIT_GRAPH_WRITE_APPEND     = (1 << 0),
 	COMMIT_GRAPH_WRITE_PROGRESS   = (1 << 1),
 	COMMIT_GRAPH_WRITE_SPLIT      = (1 << 2),
-	/* Make sure that each OID in the input is a valid commit OID. */
-	COMMIT_GRAPH_WRITE_CHECK_OIDS = (1 << 3),
-	COMMIT_GRAPH_WRITE_BLOOM_FILTERS = (1 << 4),
+	COMMIT_GRAPH_WRITE_BLOOM_FILTERS = (1 << 3),
 };
 
 enum commit_graph_split_flags {
diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index 255e3bb1c9..a79c624875 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -88,11 +88,18 @@ graph_read_expect() {
 
 test_expect_success 'exit with correct error on bad input to --stdin-commits' '
 	cd "$TRASH_DIRECTORY/full" &&
-	echo HEAD | test_expect_code 1 git commit-graph write --stdin-commits 2>stderr &&
+	# invalid, non-hex OID
+	echo HEAD >in &&
+	test_expect_code 1 git commit-graph write --stdin-commits <in 2>stderr &&
 	test_i18ngrep "unexpected non-hex object ID: HEAD" stderr &&
-	# valid tree OID, but not a commit OID
-	git rev-parse HEAD^{tree} | test_expect_code 1 git commit-graph write --stdin-commits 2>stderr &&
-	test_i18ngrep "invalid commit object id" stderr
+	# non-existent OID
+	echo $ZERO_OID >in &&
+	test_expect_code 1 git commit-graph write --stdin-commits <in 2>stderr &&
+	test_i18ngrep "invalid object" stderr &&
+	# valid commit and tree OID
+	git rev-parse HEAD HEAD^{tree} >in &&
+	git commit-graph write --stdin-commits <in &&
+	graph_read_expect 3
 '
 
 test_expect_success 'write graph' '
-- 
2.26.0.113.ge9739cdccc