Merge branch 'ds/default-pack-use-sparse-to-true'

The 'pack.useSparse' configuration variable now defaults to 'true',
enabling an optimization that has been experimental since Git 2.21.

* ds/default-pack-use-sparse-to-true:
  pack-objects: flip the use of GIT_TEST_PACK_SPARSE
  config: set pack.useSparse=true by default

Documentation/config/feature.txt

@@ -12,9 +12,6 @@ feature.experimental::
 	setting if you are interested in providing feedback on experimental
 	features. The new default values are:
 +
-* `pack.useSparse=true` uses a new algorithm when constructing a pack-file
-which can improve `git push` performance in repos with many files.
-+
 * `fetch.negotiationAlgorithm=skipping` may improve fetch negotiation times by
 skipping more commits at a time, reducing the number of round trips.
 +

Documentation/config/pack.txt

@@ -119,8 +119,8 @@ pack.useSparse::
 	objects. This can have significant performance benefits when
 	computing a pack to send a small change. However, it is possible
 	that extra objects are added to the pack-file if the included
-	commits contain certain types of direct renames. Default is `false`
+	commits contain certain types of direct renames. Default is
-	unless `feature.experimental` is enabled.
+	`true`.
 
 pack.writeBitmaps (deprecated)::
 	This is a deprecated synonym for `repack.writeBitmaps`.

Documentation/git-pack-objects.txt

@@ -14,7 +14,7 @@ SYNOPSIS
 	[--local] [--incremental] [--window=<n>] [--depth=<n>]
 	[--revs [--unpacked | --all]] [--keep-pack=<pack-name>]
 	[--stdout [--filter=<filter-spec>] | base-name]
-	[--shallow] [--keep-true-parents] [--sparse] < object-list
+	[--shallow] [--keep-true-parents] [--[no-]sparse] < object-list
 
 
 DESCRIPTION
@@ -196,14 +196,16 @@ depth is 4095.
 	Add --no-reuse-object if you want to force a uniform compression
 	level on all data no matter the source.
 
---sparse::
+--[no-]sparse::
-	Use the "sparse" algorithm to determine which objects to include in
+	Toggle the "sparse" algorithm to determine which objects to include in
 	the pack, when combined with the "--revs" option. This algorithm
 	only walks trees that appear in paths that introduce new objects.
 	This can have significant performance benefits when computing
 	a pack to send a small change. However, it is possible that extra
 	objects are added to the pack-file if the included commits contain
-	certain types of direct renames.
+	certain types of direct renames. If this option is not included,
+	it defaults to the value of `pack.useSparse`, which is true unless
+	otherwise specified.
 
 --thin::
 	Create a "thin" pack by omitting the common objects between a

builtin/pack-objects.c

@@ -3469,9 +3469,9 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 
 	read_replace_refs = 0;
 
-	sparse = git_env_bool("GIT_TEST_PACK_SPARSE", 0);
+	sparse = git_env_bool("GIT_TEST_PACK_SPARSE", -1);
 	prepare_repo_settings(the_repository);
-	if (!sparse && the_repository->settings.pack_use_sparse != -1)
+	if (sparse < 0)
 		sparse = the_repository->settings.pack_use_sparse;
 
 	reset_pack_idx_option(&pack_idx_opts);

repo-settings.c

@@ -45,6 +45,8 @@ void prepare_repo_settings(struct repository *r)
 
 	if (!repo_config_get_bool(r, "pack.usesparse", &value))
 		r->settings.pack_use_sparse = value;
+	UPDATE_DEFAULT_BOOL(r->settings.pack_use_sparse, 1);
+
 	if (!repo_config_get_bool(r, "feature.manyfiles", &value) && value) {
 		UPDATE_DEFAULT_BOOL(r->settings.index_version, 4);
 		UPDATE_DEFAULT_BOOL(r->settings.core_untracked_cache, UNTRACKED_CACHE_WRITE);
@@ -52,7 +54,6 @@ void prepare_repo_settings(struct repository *r)
 	if (!repo_config_get_bool(r, "fetch.writecommitgraph", &value))
 		r->settings.fetch_write_commit_graph = value;
 	if (!repo_config_get_bool(r, "feature.experimental", &value) && value) {
-		UPDATE_DEFAULT_BOOL(r->settings.pack_use_sparse, 1);
 		UPDATE_DEFAULT_BOOL(r->settings.fetch_negotiation_algorithm, FETCH_NEGOTIATION_SKIPPING);
 		UPDATE_DEFAULT_BOOL(r->settings.fetch_write_commit_graph, 1);
 	}

t/README

@@ -386,9 +386,9 @@ GIT_TEST_INDEX_VERSION=<n> exercises the index read/write code path
 for the index version specified.  Can be set to any valid version
 (currently 2, 3, or 4).
 
-GIT_TEST_PACK_SPARSE=<boolean> if enabled will default the pack-objects
+GIT_TEST_PACK_SPARSE=<boolean> if disabled will default the pack-objects
-builtin to use the sparse object walk. This can still be overridden by
+builtin to use the non-sparse object walk. This can still be overridden by
-the --no-sparse command-line argument.
+the --sparse command-line argument.
 
 GIT_TEST_PRELOAD_INDEX=<boolean> exercises the preload-index code path
 by overriding the minimum number of cache entries required per thread.

t/t5322-pack-objects-sparse.sh

@@ -105,14 +105,16 @@ test_expect_success 'non-sparse pack-objects' '
 	test_cmp required_objects.txt nonsparse_required_objects.txt
 '
 
+# --sparse is enabled by default by pack.useSparse
 test_expect_success 'sparse pack-objects' '
+	GIT_TEST_PACK_SPARSE=-1 &&
 	git rev-parse			\
 		topic1			\
 		topic1^{tree}		\
 		topic1:f3		\
 		topic1:f3/f4		\
 		topic1:f3/f4/data.txt | sort >expect_sparse_objects.txt &&
-	git pack-objects --stdout --revs --sparse <packinput.txt >sparse.pack &&
+	git pack-objects --stdout --revs <packinput.txt >sparse.pack &&
 	git index-pack -o sparse.idx sparse.pack &&
 	git show-index <sparse.idx | awk "{print \$2}" >sparse_objects.txt &&
 	test_cmp expect_sparse_objects.txt sparse_objects.txt