[PATCH v2 16/24] config: create core.multiPackIndex setting

[Derrick Stolee <stolee@gmail.com>]

The core.multiPackIndex config setting controls the multi-pack-
index (MIDX) feature. If false, the setting will disable all reads
from the multi-pack-index file.

Add comparison commands in t5319-multi-pack-index.sh to check
typical Git behavior remains the same as the config setting is turned
on and off. This currently includes 'git rev-list' and 'git log'
commands to trigger several object database reads.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/config.txt    |  4 +++
 cache.h                     |  1 +
 config.c                    |  5 ++++
 environment.c               |  1 +
 t/t5319-multi-pack-index.sh | 55 +++++++++++++++++++++++++++++++------
 5 files changed, 57 insertions(+), 9 deletions(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index ab641bf5a9..ab895ebb32 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -908,6 +908,10 @@ core.commitGraph::
 	Enable git commit graph feature. Allows reading from the
 	commit-graph file.
 
+core.multiPackIndex::
+	Use the multi-pack-index file to track multiple packfiles using a
+	single index. See linkgit:technical/multi-pack-index[1].
+
 core.sparseCheckout::
 	Enable "sparse checkout" feature. See section "Sparse checkout" in
 	linkgit:git-read-tree[1] for more information.
diff --git a/cache.h b/cache.h
index 89a107a7f7..d12aa49710 100644
--- a/cache.h
+++ b/cache.h
@@ -814,6 +814,7 @@ extern char *git_replace_ref_base;
 extern int fsync_object_files;
 extern int core_preload_index;
 extern int core_commit_graph;
+extern int core_multi_pack_index;
 extern int core_apply_sparse_checkout;
 extern int precomposed_unicode;
 extern int protect_hfs;
diff --git a/config.c b/config.c
index fbbf0f8e9f..95d8da4243 100644
--- a/config.c
+++ b/config.c
@@ -1313,6 +1313,11 @@ static int git_default_core_config(const char *var, const char *value)
 		return 0;
 	}
 
+	if (!strcmp(var, "core.multipackindex")) {
+		core_multi_pack_index = git_config_bool(var, value);
+		return 0;
+	}
+
 	if (!strcmp(var, "core.sparsecheckout")) {
 		core_apply_sparse_checkout = git_config_bool(var, value);
 		return 0;
diff --git a/environment.c b/environment.c
index 2a6de2330b..b9bc919cdb 100644
--- a/environment.c
+++ b/environment.c
@@ -67,6 +67,7 @@ enum object_creation_mode object_creation_mode = OBJECT_CREATION_MODE;
 char *notes_ref_name;
 int grafts_replace_parents = 1;
 int core_commit_graph;
+int core_multi_pack_index;
 int core_apply_sparse_checkout;
 int merge_log_config = -1;
 int precomposed_unicode = -1; /* see probe_utf8_pathname_composition() */
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index ccde83bca4..f7f55ea181 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -3,6 +3,8 @@
 test_description='multi-pack-indexes'
 . ./test-lib.sh
 
+objdir=.git/objects
+
 midx_read_expect() {
 	NUM_PACKS=$1
 	NUM_OBJECTS=$2
@@ -61,12 +63,42 @@ test_expect_success 'write midx with one v1 pack' '
 	midx_read_expect 1 17 4 .
 '
 
+midx_git_two_modes() {
+	git -c core.multiPackIndex=false $1 >expect &&
+	git -c core.multiPackIndex=true $1 >actual &&
+	test_cmp expect actual
+}
+
+compare_results_with_midx() {
+	MSG=$1
+	test_expect_success "check normal git operations: $MSG" '
+		midx_git_two_modes "rev-list --objects --all" &&
+		midx_git_two_modes "log --raw"
+	'
+}
+
 test_expect_success 'write midx with one v2 pack' '
-	git pack-objects --index-version=2,0x40 pack/test <obj-list &&
-	git multi-pack-index --object-dir=. write &&
-	midx_read_expect 1 17 4 .
+	git pack-objects --index-version=2,0x40 $objdir/pack/test <obj-list &&
+	git multi-pack-index --object-dir=$objdir write &&
+	midx_read_expect 1 17 4 $objdir
 '
 
+midx_git_two_modes() {
+	git -c core.multiPackIndex=false $1 >expect &&
+	git -c core.multiPackIndex=true $1 >actual &&
+	test_cmp expect actual
+}
+
+compare_results_with_midx() {
+	MSG=$1
+	test_expect_success "check normal git operations: $MSG" '
+		midx_git_two_modes "rev-list --objects --all" &&
+		midx_git_two_modes "log --raw"
+	'
+}
+
+compare_results_with_midx "one v2 pack"
+
 test_expect_success 'Add more objects' '
 	for i in `test_seq 6 10`
 	do
@@ -92,11 +124,13 @@ test_expect_success 'Add more objects' '
 '
 
 test_expect_success 'write midx with two packs' '
-	git pack-objects --index-version=1 pack/test-2 <obj-list2 &&
-	git multi-pack-index --object-dir=. write &&
-	midx_read_expect 2 33 4 .
+	git pack-objects --index-version=1 $objdir/pack/test-2 <obj-list2 &&
+	git multi-pack-index --object-dir=$objdir write &&
+	midx_read_expect 2 33 4 $objdir
 '
 
+compare_results_with_midx "two packs"
+
 test_expect_success 'Add more packs' '
 	for j in `test_seq 1 10`
 	do
@@ -117,17 +151,20 @@ test_expect_success 'Add more packs' '
 		git ls-tree $tree | sed -e "s/.* \\([0-9a-f]*\\)	.*/\\1/"
 		} >obj-list &&
 		git update-ref HEAD $commit &&
-		git pack-objects --index-version=2 pack/test-pack <obj-list &&
+		git pack-objects --index-version=2 $objdir/pack/test-pack <obj-list &&
 		i=$(expr $i + 1) || return 1 &&
 		j=$(expr $j + 1) || return 1
 	done
 '
 
+compare_results_with_midx "mixed mode (two packs + extra)"
+
 test_expect_success 'write midx with twelve packs' '
-	git multi-pack-index --object-dir=. write &&
-	midx_read_expect 12 73 4 .
+	git multi-pack-index --object-dir=$objdir write &&
+	midx_read_expect 12 73 4 $objdir
 '
 
+compare_results_with_midx "twelve packs"
 
 # usage: corrupt_data <file> <pos> [<data>]
 corrupt_data() {
-- 
2.18.0.24.g1b579a2ee9