repack: silence warnings when auto-enabled bitmaps cannot be built

Depending on various config options, a full repack may not be able to
build a reachability bitmap index (e.g., if pack.packSizeLimit forces us
to write multiple packs). In these cases pack-objects may write a
warning to stderr.

Since 36eba032 (repack: enable bitmaps by default on bare repos,
2019-03-14), we may generate these warnings even when the user did not
explicitly ask for bitmaps. This has two downsides:

  - it can be confusing, if they don't know what bitmaps are

  - a daemonized auto-gc will write this to its log file, and the
    presence of the warning may suppress further auto-gc (until
    gc.logExpiry has elapsed)

Let's have repack communicate to pack-objects that the choice to turn on
bitmaps was not made explicitly by the user, which in turn allows
pack-objects to suppress these warnings.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/pack-objects.c

@@ -96,7 +96,11 @@ static off_t reuse_packfile_offset;
 
 static int use_bitmap_index_default = 1;
 static int use_bitmap_index = -1;
-static int write_bitmap_index;
+static enum {
+	WRITE_BITMAP_FALSE = 0,
+	WRITE_BITMAP_QUIET,
+	WRITE_BITMAP_TRUE,
+} write_bitmap_index;
 static uint16_t write_bitmap_options = BITMAP_OPT_HASH_CACHE;
 
 static int exclude_promisor_objects;
@@ -892,7 +896,8 @@ static void write_pack_file(void)
 						 nr_written, oid.hash, offset);
 			close(fd);
 			if (write_bitmap_index) {
-				warning(_(no_split_warning));
+				if (write_bitmap_index != WRITE_BITMAP_QUIET)
+					warning(_(no_split_warning));
 				write_bitmap_index = 0;
 			}
 		}
@@ -1176,7 +1181,8 @@ static int add_object_entry(const struct object_id *oid, enum object_type type,
 	if (!want_object_in_pack(oid, exclude, &found_pack, &found_offset)) {
 		/* The pack is missing an object, so it will not have closure */
 		if (write_bitmap_index) {
-			warning(_(no_closure_warning));
+			if (write_bitmap_index != WRITE_BITMAP_QUIET)
+				warning(_(no_closure_warning));
 			write_bitmap_index = 0;
 		}
 		return 0;
@@ -3313,8 +3319,13 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 			    N_("do not hide commits by grafts"), 0),
 		OPT_BOOL(0, "use-bitmap-index", &use_bitmap_index,
 			 N_("use a bitmap index if available to speed up counting objects")),
-		OPT_BOOL(0, "write-bitmap-index", &write_bitmap_index,
-			 N_("write a bitmap index together with the pack index")),
+		OPT_SET_INT(0, "write-bitmap-index", &write_bitmap_index,
+			    N_("write a bitmap index together with the pack index"),
+			    WRITE_BITMAP_TRUE),
+		OPT_SET_INT_F(0, "write-bitmap-index-quiet",
+			      &write_bitmap_index,
+			      N_("write a bitmap index if possible"),
+			      WRITE_BITMAP_QUIET, PARSE_OPT_HIDDEN),
 		OPT_PARSE_LIST_OBJECTS_FILTER(&filter_options),
 		{ OPTION_CALLBACK, 0, "missing", NULL, N_("action"),
 		  N_("handling for missing objects"), PARSE_OPT_NONEG,

builtin/repack.c

@@ -345,13 +345,14 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 		die(_("--keep-unreachable and -A are incompatible"));
 
 	if (write_bitmaps < 0) {
-		write_bitmaps = (pack_everything & ALL_INTO_ONE) &&
-				 is_bare_repository() &&
-				 keep_pack_list.nr == 0 &&
-				 !has_pack_keep_file();
+		if (!(pack_everything & ALL_INTO_ONE) ||
+		    !is_bare_repository() ||
+		    keep_pack_list.nr != 0 ||
+		    has_pack_keep_file())
+			write_bitmaps = 0;
 	}
 	if (pack_kept_objects < 0)
-		pack_kept_objects = write_bitmaps;
+		pack_kept_objects = !!write_bitmaps;
 
 	if (write_bitmaps && !(pack_everything & ALL_INTO_ONE))
 		die(_(incremental_bitmap_conflict_error));
@@ -375,8 +376,10 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 	argv_array_push(&cmd.args, "--indexed-objects");
 	if (repository_format_partial_clone)
 		argv_array_push(&cmd.args, "--exclude-promisor-objects");
-	if (write_bitmaps)
+	if (write_bitmaps > 0)
 		argv_array_push(&cmd.args, "--write-bitmap-index");
+	else if (write_bitmaps < 0)
+		argv_array_push(&cmd.args, "--write-bitmap-index-quiet");
 	if (use_delta_islands)
 		argv_array_push(&cmd.args, "--delta-islands");
 

t/t7700-repack.sh

@@ -250,4 +250,15 @@ test_expect_success 'no bitmaps created if .keep files present' '
 	test_must_be_empty actual
 '
 
+test_expect_success 'auto-bitmaps do not complain if unavailable' '
+	test_config -C bare.git pack.packSizeLimit 1M &&
+	blob=$(test-tool genrandom big $((1024*1024)) |
+	       git -C bare.git hash-object -w --stdin) &&
+	git -C bare.git update-ref refs/tags/big $blob &&
+	git -C bare.git repack -ad 2>stderr &&
+	test_must_be_empty stderr &&
+	find bare.git/objects/pack -type f -name "*.bitmap" >actual &&
+	test_must_be_empty actual
+'
+
 test_done