Merge branch 'ds/early-access' into jch

A mechanism to enable newish configuration settings in bulk has
been invented.

The model may need to be rethought.  A linear scale with "early
adoption" mindset may not match diverse use cases of the tool.

* ds/early-access:
  repo-settings: pack.useSparse=true
  repo-settings: use index.version=4 by default
  repo-settings: create core.featureAdoptionRate setting

Author: gitster

Documentation/config/core.txt

@@ -577,7 +577,8 @@ the `GIT_NOTES_REF` environment variable.  See linkgit:git-notes[1].
 
 core.commitGraph::
 	If true, then git will read the commit-graph file (if it exists)
-	to parse the graph structure of commits. Defaults to false. See
+	to parse the graph structure of commits. Defaults to false, unless
+	`core.featureAdoptionRate` is at least three. See
 	linkgit:git-commit-graph[1] for more information.
 
 core.useReplaceRefs::
@@ -601,3 +602,34 @@ core.abbrev::
 	in your repository, which hopefully is enough for
 	abbreviated object names to stay unique for some time.
 	The minimum length is 4.
+
+core.featureAdoptionRate::
+	Set an integer value on a scale from 0 to 10 describing your
+	desire to adopt new performance features. Defaults to 0. As
+	the value increases, features are enabled by changing the
+	default values of other config settings. If a config variable
+	is specified explicitly, the explicit value will override these
+	defaults:
++
+If the value is at least 3, then the following defaults are modified.
+These represent relatively new features that have existed for multiple
+major releases, and may present performance benefits. These benefits
+depend on the amount and kind of data in your repo and how you use it.
+The settings do not modify the user-facing output of porcelain commands.
++
+* `core.commitGraph=true` enables reading commit-graph files.
++
+* `gc.writeCommitGraph=true` eneables writing commit-graph files during
+`git gc`.
++
+* `index.version=4` uses prefix-compression to reduce the size of the
+.git/index file.
++
+If the value is at least 5, then all of the defaults above are included,
+plus the defaults below. These represent new features that present
+significant performance benefits, but may not have been released for
+multiple major versions.
++
+* `pack.useSparse=true` uses the sparse tree-walk algorithm, which is
+optimized for enumerating objects during linkgit:git-push[1] from a
+client machine.

Documentation/config/gc.txt

@@ -63,8 +63,8 @@ gc.writeCommitGraph::
 	If true, then gc will rewrite the commit-graph file when
 	linkgit:git-gc[1] is run. When using `git gc --auto`
 	the commit-graph will be updated if housekeeping is
-	required. Default is false. See linkgit:git-commit-graph[1]
-	for details.
+	required. Default is false, unless `core.featureAdoptionRage`
+	is at least three. See linkgit:git-commit-graph[1] for details.
 
 gc.logExpiry::
 	If the file gc.log exists, then `git gc --auto` will print

Documentation/config/index.txt

@@ -24,3 +24,5 @@ index.threads::
 index.version::
 	Specify the version with which new index files should be
 	initialized.  This does not affect existing repositories.
+	If `core.featureAdoptionRate` is at least three, then the
+	default value is 4.

Documentation/config/pack.txt

@@ -112,7 +112,8 @@ 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.
+	commits contain certain types of direct renames. Defaults to
+	false, unless `core.featureAdoptionRate` is at least five.
 
 pack.writeBitmaps (deprecated)::
 	This is a deprecated synonym for `repack.writeBitmaps`.

Makefile

@@ -965,6 +965,7 @@ LIB_OBJS += refspec.o
 LIB_OBJS += ref-filter.o
 LIB_OBJS += remote.o
 LIB_OBJS += replace-object.o
+LIB_OBJS += repo-settings.o
 LIB_OBJS += repository.o
 LIB_OBJS += rerere.o
 LIB_OBJS += resolve-undo.o

builtin/gc.c

@@ -27,6 +27,7 @@
 #include "pack-objects.h"
 #include "blob.h"
 #include "tree.h"
+#include "repo-settings.h"
 
 #define FAILED_RUN "failed to run %s"
 
@@ -41,7 +42,6 @@ static int aggressive_depth = 50;
 static int aggressive_window = 250;
 static int gc_auto_threshold = 6700;
 static int gc_auto_pack_limit = 50;
-static int gc_write_commit_graph;
 static int detach_auto = 1;
 static timestamp_t gc_log_expire_time;
 static const char *gc_log_expire = "1.day.ago";
@@ -148,7 +148,6 @@ static void gc_config(void)
 	git_config_get_int("gc.aggressivedepth", &aggressive_depth);
 	git_config_get_int("gc.auto", &gc_auto_threshold);
 	git_config_get_int("gc.autopacklimit", &gc_auto_pack_limit);
-	git_config_get_bool("gc.writecommitgraph", &gc_write_commit_graph);
 	git_config_get_bool("gc.autodetach", &detach_auto);
 	git_config_get_expiry("gc.pruneexpire", &prune_expire);
 	git_config_get_expiry("gc.worktreepruneexpire", &prune_worktrees_expire);
@@ -685,7 +684,8 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 		clean_pack_garbage();
 	}
 
-	if (gc_write_commit_graph &&
+	prepare_repo_settings(the_repository);
+	if (the_repository->settings->gc_write_commit_graph == 1 &&
 	    write_commit_graph_reachable(get_object_directory(),
 					 !quiet && !daemonized ? COMMIT_GRAPH_PROGRESS : 0,
 					 NULL))

builtin/pack-objects.c

@@ -34,6 +34,7 @@
 #include "dir.h"
 #include "midx.h"
 #include "trace2.h"
+#include "repo-settings.h"
 
 #define IN_PACK(obj) oe_in_pack(&to_pack, obj)
 #define SIZE(obj) oe_size(&to_pack, obj)
@@ -2709,10 +2710,6 @@ static int git_pack_config(const char *k, const char *v, void *cb)
 		use_bitmap_index_default = git_config_bool(k, v);
 		return 0;
 	}
-	if (!strcmp(k, "pack.usesparse")) {
-		sparse = git_config_bool(k, v);
-		return 0;
-	}
 	if (!strcmp(k, "pack.threads")) {
 		delta_search_threads = git_config_int(k, v);
 		if (delta_search_threads < 0)
@@ -3332,6 +3329,10 @@ 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);
+	prepare_repo_settings(the_repository);
+	if (!sparse && the_repository->settings->pack_use_sparse != -1)
+		sparse = the_repository->settings->pack_use_sparse;
+
 	reset_pack_idx_option(&pack_idx_opts);
 	git_config(git_pack_config, NULL);
 

commit-graph.c

@@ -16,6 +16,7 @@
 #include "hashmap.h"
 #include "replace-object.h"
 #include "progress.h"
+#include "repo-settings.h"
 
 #define GRAPH_SIGNATURE 0x43475048 /* "CGPH" */
 #define GRAPH_CHUNKID_OIDFANOUT 0x4f494446 /* "OIDF" */
@@ -466,7 +467,6 @@ static void prepare_commit_graph_one(struct repository *r, const char *obj_dir)
 static int prepare_commit_graph(struct repository *r)
 {
 	struct object_directory *odb;
-	int config_value;
 
 	if (git_env_bool(GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD, 0))
 		die("dying as requested by the '%s' variable on commit-graph load!",
@@ -476,9 +476,10 @@ static int prepare_commit_graph(struct repository *r)
 		return !!r->objects->commit_graph;
 	r->objects->commit_graph_attempted = 1;
 
+	prepare_repo_settings(r);
+
 	if (!git_env_bool(GIT_TEST_COMMIT_GRAPH, 0) &&
-	    (repo_config_get_bool(r, "core.commitgraph", &config_value) ||
-	    !config_value))
+	    r->settings->core_commit_graph != 1)
 		/*
 		 * This repository is not configured to use commit graphs, so
 		 * do not load one. (But report commit_graph_attempted anyway

read-cache.c

@@ -25,6 +25,7 @@
 #include "fsmonitor.h"
 #include "thread-utils.h"
 #include "progress.h"
+#include "repo-settings.h"
 #include "json-writer.h"
 
 /* Mask for the name length in ce_flags in the on-disk index */
@@ -1600,16 +1601,17 @@ struct cache_entry *refresh_cache_entry(struct index_state *istate,
 
 #define INDEX_FORMAT_DEFAULT 3
 
-static unsigned int get_index_format_default(void)
+static unsigned int get_index_format_default(struct repository *r)
 {
 	char *envversion = getenv("GIT_INDEX_VERSION");
 	char *endp;
-	int value;
 	unsigned int version = INDEX_FORMAT_DEFAULT;
 
 	if (!envversion) {
-		if (!git_config_get_int("index.version", &value))
-			version = value;
+		prepare_repo_settings(r);
+
+		if (r->settings->index_version >= 0)
+			version = r->settings->index_version;
 		if (version < INDEX_FORMAT_LB || INDEX_FORMAT_UB < version) {
 			warning(_("index.version set, but the value is invalid.\n"
 				  "Using version %i"), INDEX_FORMAT_DEFAULT);
@@ -2876,7 +2878,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 	}
 
 	if (!istate->version) {
-		istate->version = get_index_format_default();
+		istate->version = get_index_format_default(the_repository);
 		if (git_env_bool("GIT_TEST_SPLIT_INDEX", 0))
 			init_split_index(istate);
 	}

repo-settings.c

@@ -0,0 +1,58 @@
+#include "cache.h"
+#include "repository.h"
+#include "config.h"
+#include "repo-settings.h"
+
+#define UPDATE_DEFAULT(s,v) do { if (s == -1) { s = v; } } while(0)
+
+static int git_repo_config(const char *key, const char *value, void *cb)
+{
+	struct repo_settings *rs = (struct repo_settings *)cb;
+
+	if (!strcmp(key, "core.featureadoptionrate")) {
+		int rate = git_config_int(key, value);
+		if (rate >= 3) {
+			UPDATE_DEFAULT(rs->core_commit_graph, 1);
+			UPDATE_DEFAULT(rs->gc_write_commit_graph, 1);
+			UPDATE_DEFAULT(rs->index_version, 4);
+		}
+		if (rate >= 5) {
+			UPDATE_DEFAULT(rs->pack_use_sparse, 1);
+		}
+		return 0;
+	}
+	if (!strcmp(key, "core.commitgraph")) {
+		rs->core_commit_graph = git_config_bool(key, value);
+		return 0;
+	}
+	if (!strcmp(key, "gc.writecommitgraph")) {
+		rs->gc_write_commit_graph = git_config_bool(key, value);
+		return 0;
+	}
+	if (!strcmp(key, "pack.usesparse")) {
+		rs->pack_use_sparse = git_config_bool(key, value);
+		return 0;
+	}
+	if (!strcmp(key, "index.version")) {
+		rs->index_version = git_config_int(key, value);
+		return 0;
+	}
+
+	return 1;
+}
+
+void prepare_repo_settings(struct repository *r)
+{
+	if (r->settings)
+		return;
+
+	r->settings = xmalloc(sizeof(*r->settings));
+
+	/* Defaults */
+	r->settings->core_commit_graph = -1;
+	r->settings->gc_write_commit_graph = -1;
+	r->settings->pack_use_sparse = -1;
+	r->settings->index_version = -1;
+
+	repo_config(r, git_repo_config, r->settings);
+}

repo-settings.h

@@ -0,0 +1,15 @@
+#ifndef REPO_SETTINGS_H
+#define REPO_SETTINGS_H
+
+struct repo_settings {
+	int core_commit_graph;
+	int gc_write_commit_graph;
+	int pack_use_sparse;
+	int index_version;
+};
+
+struct repository;
+
+void prepare_repo_settings(struct repository *r);
+
+#endif /* REPO_SETTINGS_H */

repository.h

@@ -4,6 +4,7 @@
 #include "path.h"
 
 struct config_set;
+struct repo_settings;
 struct git_hash_algo;
 struct index_state;
 struct lock_file;
@@ -72,6 +73,8 @@ struct repository {
 	 */
 	char *submodule_prefix;
 
+	struct repo_settings *settings;
+
 	/* Subsystems */
 	/*
 	 * Repository's config which contains key-value pairs from the usual

t/t1600-index.sh

@@ -59,17 +59,41 @@ test_expect_success 'out of bounds index.version issues warning' '
 	)
 '
 
-test_expect_success 'GIT_INDEX_VERSION takes precedence over config' '
+test_index_version () {
+	INDEX_VERSION_CONFIG=$1 &&
+	REPO_ADOPTION_RATE=$2 &&
+	ENV_VAR_VERSION=$3
+	EXPECTED_OUTPUT_VERSION=$4 &&
 	(
 		rm -f .git/index &&
-		GIT_INDEX_VERSION=4 &&
-		export GIT_INDEX_VERSION &&
-		git config --add index.version 2 &&
+		rm -f .git/config &&
+		if test "$INDEX_VERSION_CONFIG" -ne 0
+		then
+			git config --add index.version $INDEX_VERSION_CONFIG
+		fi &&
+		if test "$REPO_ADOPTION_RATE" -ne 0
+		then
+			git config --add core.featureAdoptionRate $REPO_ADOPTION_RATE
+		fi &&
+		if test "$ENV_VAR_VERSION" -ne 0
+		then
+			GIT_INDEX_VERSION=$ENV_VAR_VERSION &&
+			export GIT_INDEX_VERSION
+		else
+			unset GIT_INDEX_VERSION
+		fi &&
 		git add a 2>&1 &&
-		echo 4 >expect &&
+		echo $EXPECTED_OUTPUT_VERSION >expect &&
 		test-tool index-version <.git/index >actual &&
 		test_cmp expect actual
 	)
+}
+
+test_expect_success 'index version config precedence' '
+	test_index_version 2 0 4 4 &&
+	test_index_version 2 3 0 2 &&
+	test_index_version 0 3 0 4 &&
+	test_index_version 0 3 2 2
 '
 
 test_done