[PATCH v4 5/6] pack-objects: create pack.useSparse setting

[Derrick Stolee via GitGitGadget]

From: Derrick Stolee <dsto...@microsoft.com>

The '--sparse' flag in 'git pack-objects' changes the algorithm
used to enumerate objects to one that is faster for individual
users pushing new objects that change only a small cone of the
working directory. The sparse algorithm is not recommended for a
server, which likely sends new objects that appear across the
entire working directory.

Create a 'pack.useSparse' setting that enables this new algorithm.
This allows 'git push' to use this algorithm without passing a
'--sparse' flag all the way through four levels of run_command()
calls.

If the '--no-sparse' flag is set, then this config setting is
overridden.

Signed-off-by: Derrick Stolee <dsto...@microsoft.com>
---
 Documentation/config/pack.txt  |  9 +++++++++
 builtin/pack-objects.c         |  4 ++++
 t/t5322-pack-objects-sparse.sh | 15 +++++++++++++++
 3 files changed, 28 insertions(+)

diff --git a/Documentation/config/pack.txt b/Documentation/config/pack.txt
index edac75c83f..425c73aa52 100644
--- a/Documentation/config/pack.txt
+++ b/Documentation/config/pack.txt
@@ -105,6 +105,15 @@ pack.useBitmaps::
        true. You should not generally need to turn this off unless
        you are debugging pack bitmaps.
 
+pack.useSparse::
+       When true, git will default to using the '--sparse' option in
+       'git pack-objects' when the '--revs' option is present. 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.
+
 pack.writeBitmaps (deprecated)::
        This is a deprecated synonym for `repack.writeBitmaps`.
 
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 7d5b0735e3..124b1bafc4 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -2711,6 +2711,10 @@ 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)
diff --git a/t/t5322-pack-objects-sparse.sh b/t/t5322-pack-objects-sparse.sh
index 45dba6e014..8f5699bd91 100755
--- a/t/t5322-pack-objects-sparse.sh
+++ b/t/t5322-pack-objects-sparse.sh
@@ -121,4 +121,19 @@ test_expect_success 'sparse pack-objects' '
        test_cmp expect_sparse_objects.txt sparse_objects.txt
 '
 
+test_expect_success 'pack.useSparse enables algorithm' '
+       git config pack.useSparse true &&
+       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
+'
+
+test_expect_success 'pack.useSparse overridden' '
+       git pack-objects --stdout --revs --no-sparse <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_objects.txt sparse_objects.txt
+'
+
 test_done
-- 
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