[PATCH] commit-graph: warn about incompatibilities only when trying to write

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

In c85eec7fc37 (commit-graph: when incompatible with graphs, indicate
why, 2021-02-11), we started warning the user if they tried to write a
commit-graph in a shallow repository, or one containing replace objects.

However, this patch was a bit overzealous, as Git now _also_ warns when
merely checking whether there _is_ a usable commit graph, not only when
writing one.

Let's suppress that warning unless we want to write a commit-graph.

Reported-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
    commit-graph: warn about incompatibilities only when trying to write
    
    As pointed out by Ævar in
    https://lore.kernel.org/git/87pn0o6y1e.fsf@evledraar.gmail.com, my
    recent patch to trigger warnings in repositories that are incompatible
    with the commit-graph was a bit too overzealous. Here is a fix for that.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-888%2Fdscho%2Fwarn-a-little-less-if-commit-graph-is-skipped-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-888/dscho/warn-a-little-less-if-commit-graph-is-skipped-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/888

 commit-graph.c          | 20 ++++++++++++--------
 t/t5318-commit-graph.sh | 13 +++++++++++++
 2 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/commit-graph.c b/commit-graph.c
index 8fd480434353..245b7108e0d1 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -198,7 +198,7 @@ static struct commit_graph *alloc_commit_graph(void)
 
 extern int read_replace_refs;
 
-static int commit_graph_compatible(struct repository *r)
+static int commit_graph_compatible(struct repository *r, int quiet)
 {
 	if (!r->gitdir)
 		return 0;
@@ -206,8 +206,9 @@ static int commit_graph_compatible(struct repository *r)
 	if (read_replace_refs) {
 		prepare_replace_object(r);
 		if (hashmap_get_size(&r->objects->replace_map->map)) {
-			warning(_("repository contains replace objects; "
-			       "skipping commit-graph"));
+			if (!quiet)
+				warning(_("repository contains replace "
+					  "objects; skipping commit-graph"));
 			return 0;
 		}
 	}
@@ -215,12 +216,15 @@ static int commit_graph_compatible(struct repository *r)
 	prepare_commit_graft(r);
 	if (r->parsed_objects &&
 	    (r->parsed_objects->grafts_nr || r->parsed_objects->substituted_parent)) {
-		warning(_("repository contains (deprecated) grafts; "
-		       "skipping commit-graph"));
+		if (!quiet)
+			warning(_("repository contains (deprecated) grafts; "
+			       "skipping commit-graph"));
 		return 0;
 	}
 	if (is_repository_shallow(r)) {
-		warning(_("repository is shallow; skipping commit-graph"));
+		if (!quiet)
+			warning(_("repository is shallow; skipping "
+				  "commit-graph"));
 		return 0;
 	}
 
@@ -652,7 +656,7 @@ static int prepare_commit_graph(struct repository *r)
 		 */
 		return 0;
 
-	if (!commit_graph_compatible(r))
+	if (!commit_graph_compatible(r, 1))
 		return 0;
 
 	prepare_alt_odb(r);
@@ -2123,7 +2127,7 @@ int write_commit_graph(struct object_directory *odb,
 		warning(_("attempting to write a commit-graph, but 'core.commitGraph' is disabled"));
 		return 0;
 	}
-	if (!commit_graph_compatible(the_repository))
+	if (!commit_graph_compatible(the_repository, 0))
 		return 0;
 
 	ctx = xcalloc(1, sizeof(struct write_commit_graph_context));
diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index 2ed0c1544da1..2699c55e9a93 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -741,4 +741,17 @@ test_expect_success 'corrupt commit-graph write (missing tree)' '
 	)
 '
 
+test_expect_success 'warn about incompatibilities (only) when writing' '
+	git init warn &&
+	test_commit -C warn initial &&
+	test_commit -C warn second &&
+	git -C warn replace --graft second &&
+	test_config -C warn gc.writecommitgraph true &&
+
+	git -C warn gc 2>err &&
+	test_i18ngrep "skipping commit-graph" err &&
+	git -C warn rev-list -1 second 2>err &&
+	test_i18ngrep ! "skipping commit-graph" err
+'
+
 test_done

base-commit: c85eec7fc37e1ca79072f263ae6ea1ee305ba38c
-- 
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