[PATCH v1 1/2] builtin/grep.c: add --sparse option

[Shaoxuan Yuan <shaoxuan.yuan02@gmail.com>]

Add a --sparse option to `git-grep`. This option is mainly used to:

If searching in the index (using --cached):

With --sparse, proceed the action when the current cache_entry is
marked with SKIP_WORKTREE bit (the default is to skip this kind of
entry). Before this patch, --cached itself can realize this action.
Adding --sparse here grants the user finer control over sparse
entries. If the user only wants to peak into the index without
caring about sparse entries, --cached should suffice; if the user
wants to peak into the index _and_ cares about sparse entries,
combining --sparse with --cached can address this need.

Suggested-by: Victoria Dye <vdye@github.com>
Signed-off-by: Shaoxuan Yuan <shaoxuan.yuan02@gmail.com>
---
 builtin/grep.c                  | 10 +++++++++-
 t/t7817-grep-sparse-checkout.sh | 12 ++++++------
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/builtin/grep.c b/builtin/grep.c
index e6bcdf860c..61402e8084 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -96,6 +96,8 @@ static pthread_cond_t cond_result;
 
 static int skip_first_line;
 
+static int grep_sparse = 0;
+
 static void add_work(struct grep_opt *opt, struct grep_source *gs)
 {
 	if (opt->binary != GREP_BINARY_TEXT)
@@ -525,7 +527,11 @@ static int grep_cache(struct grep_opt *opt,
 	for (nr = 0; nr < repo->index->cache_nr; nr++) {
 		const struct cache_entry *ce = repo->index->cache[nr];
 
-		if (!cached && ce_skip_worktree(ce))
+		/*
+		 * If ce is a SKIP_WORKTREE entry, look into it when both
+		 * --sparse and --cached are given.
+		 */
+		if (!(grep_sparse && cached) && ce_skip_worktree(ce))
 			continue;
 
 		strbuf_setlen(&name, name_base_len);
@@ -963,6 +969,8 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 			   PARSE_OPT_NOCOMPLETE),
 		OPT_INTEGER('m', "max-count", &opt.max_count,
 			N_("maximum number of results per file")),
+		OPT_BOOL(0, "sparse", &grep_sparse,
+			 N_("search sparse contents and expand sparse index")),
 		OPT_END()
 	};
 	grep_prefix = prefix;
diff --git a/t/t7817-grep-sparse-checkout.sh b/t/t7817-grep-sparse-checkout.sh
index eb59564565..ca71f526eb 100755
--- a/t/t7817-grep-sparse-checkout.sh
+++ b/t/t7817-grep-sparse-checkout.sh
@@ -118,13 +118,13 @@ test_expect_success 'grep searches unmerged file despite not matching sparsity p
 	test_cmp expect actual
 '
 
-test_expect_success 'grep --cached searches entries with the SKIP_WORKTREE bit' '
+test_expect_success 'grep --cached and --sparse searches entries with the SKIP_WORKTREE bit' '
 	cat >expect <<-EOF &&
 	a:text
 	b:text
 	dir/c:text
 	EOF
-	git grep --cached "text" >actual &&
+	git grep --cached --sparse "text" >actual &&
 	test_cmp expect actual
 '
 
@@ -143,7 +143,7 @@ test_expect_success 'grep --recurse-submodules honors sparse checkout in submodu
 	test_cmp expect actual
 '
 
-test_expect_success 'grep --recurse-submodules --cached searches entries with the SKIP_WORKTREE bit' '
+test_expect_success 'grep --recurse-submodules --cached and --sparse searches entries with the SKIP_WORKTREE bit' '
 	cat >expect <<-EOF &&
 	a:text
 	b:text
@@ -152,7 +152,7 @@ test_expect_success 'grep --recurse-submodules --cached searches entries with th
 	sub/B/b:text
 	sub2/a:text
 	EOF
-	git grep --recurse-submodules --cached "text" >actual &&
+	git grep --recurse-submodules --cached --sparse "text" >actual &&
 	test_cmp expect actual
 '
 
@@ -166,7 +166,7 @@ test_expect_success 'working tree grep does not search the index with CE_VALID a
 	test_cmp expect actual
 '
 
-test_expect_success 'grep --cached searches index entries with both CE_VALID and SKIP_WORKTREE' '
+test_expect_success 'grep --cached and --sparse searches index entries with both CE_VALID and SKIP_WORKTREE' '
 	cat >expect <<-EOF &&
 	a:text
 	b:text
@@ -174,7 +174,7 @@ test_expect_success 'grep --cached searches index entries with both CE_VALID and
 	EOF
 	test_when_finished "git update-index --no-assume-unchanged b" &&
 	git update-index --assume-unchanged b &&
-	git grep --cached text >actual &&
+	git grep --cached --sparse text >actual &&
 	test_cmp expect actual
 '
 
-- 
2.37.0