[RPC] grep: introduce --scope option

Because we may want to restrict grep's file scope
to sparse specification, Apply the --scope option
we implemented in diff to grep as well.

`--scope=sparse` mean that the search file scope
restrict to sparse specification when we grep
something in commit history, and `--scope=all`
mean that the search file scope will be full-tree.

Note that `--scope` option only oly takes effect
when "git grep <tree>" is specified.

Signed-off-by: ZheNing Hu <adlternative@gmail.com>

Documentation/git-grep.txt

@@ -28,6 +28,7 @@ SYNOPSIS
 	   [-f <file>] [-e] <pattern>
 	   [--and|--or|--not|(|)|-e <pattern>...]
 	   [--recurse-submodules] [--parent-basename <basename>]
+	   [--scope=(sparse|all)]
 	   [ [--[no-]exclude-standard] [--cached | --no-index | --untracked] | <tree>...]
 	   [--] [<pathspec>...]
 
@@ -296,6 +297,29 @@ question doesn't support them.
 	Do not output matched lines; instead, exit with status 0 when
 	there is a match and with non-zero status when there isn't.
 
+--scope=(sparse|all)::
+	Restrict or not restrict grep path scope in sparse specification.
+	The variants are as follows:
+
++
+--
+`sparse`;;
+	When grep in commit history, restrict the scope of file path
+	to the sparse specification. See sparse specification in
+	link:technical/sparse-checkout.html [the sparse-checkout design
+	document] for more information.
+`all`;;
+	When grep in commit history, the file path scope is full-tree.
+	This is consistent with the current default behavior.
+--
++
+
+Note that `--scope` option only take effect if git command specify `<tree>`.
+
+The behavior of this `--scope` option is experimental and may change
+in the future. See link:technical/sparse-checkout.html [the sparse-checkout
+design document] for more information.
+
 <tree>...::
 	Instead of searching tracked files in the working tree, search
 	blobs in the given trees.

builtin/grep.c

@@ -640,6 +640,15 @@ static int grep_tree(struct grep_opt *opt, const struct pathspec *pathspec,
 		}
 
 		strbuf_add(base, entry.path, te_len);
+		if (opt->scope == SPARSE_SCOPE_SPARSE &&
+			base->len != tn_len &&
+			!path_in_sparse_patterns(base->buf + tn_len,
+					S_ISDIR(entry.mode) ||
+					S_ISGITLINK(entry.mode))) {
+			strbuf_setlen(base, old_baselen);
+			continue;
+		}
+
 
 		if (S_ISREG(entry.mode)) {
 			hit |= grep_oid(opt, &entry.oid, base->buf, tn_len,
@@ -999,6 +1008,7 @@ 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_SPARSE_SCOPE(&opt.scope),
 		OPT_END()
 	};
 	grep_prefix = prefix;

grep.h

@@ -22,6 +22,7 @@ typedef int pcre2_general_context;
 #endif
 #include "thread-utils.h"
 #include "userdiff.h"
+#include "cache.h"
 
 struct repository;
 
@@ -175,6 +176,7 @@ struct grep_opt {
 
 	void (*output)(struct grep_opt *opt, const void *data, size_t size);
 	void *output_priv;
+	enum sparse_scope scope;
 };
 
 #define GREP_OPT_INIT { \

t/t1090-sparse-checkout-scope.sh

@@ -382,4 +382,31 @@ M	in
 	test_cmp expected actual
 '
 
+# git grep TREE
+
+test_expect_success 'git grep --scope=all' '
+	reset_sparse_checkout_state &&
+	cat >expected <<-EOF &&
+HEAD~:in/1
+HEAD~:out1/1
+HEAD~:out1/2
+HEAD~:out1/3
+HEAD~:out1/4
+HEAD~:out1/5
+HEAD~:out1/6
+HEAD~:out2/1
+	EOF
+	git -C repo grep --name-only --scope=all 1 HEAD~ >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'git grep --scope=sparse' '
+	reset_sparse_checkout_state &&
+	cat >expected <<-EOF &&
+HEAD~:in/1
+	EOF
+	git -C repo grep --name-only --scope=sparse 1 HEAD~ >actual &&
+	test_cmp expected actual
+'
+
 test_done