sparse-checkout: pass string literals directly to add_pattern()

The add_pattern() function takes a pattern string, but neither makes a
copy of it nor takes ownership of the memory. So it is the caller's
responsibility to make sure the string hangs around as long as the
pattern_list which references it.

There are a few cases in sparse-checkout where we use string literal
patterns by stuffing them into a strbuf, detaching the buffer, and then
passing the result into add_pattern(). This creates a leak when the
pattern_list is eventually cleared, since we don't retain a copy of the
detached buffer to free.

But we can observe that the whole strbuf dance is unnecessary. The point
was presumably[1] to satisfy the lifetime requirement of the string. But
string literals have static duration; we can count on them lasting for
the whole program.

So we can fix the leak by just passing them directly. And as a bonus,
that simplifies the code. The leaks can be seen in t7002, which drops
from 25 leaks to 22 with this patch. It also makes t3602 and t1090
leak-free.

In the long run, we will also want to clean up this (undocumented!)
memory lifetime requirement of add_pattern(). But that can come in a
later patch; passing the string literals directly will be the right
thing either way.

[1] The code in question comes from 416adc8711 (sparse-checkout: update
    working directory in-process for 'init', 2019-11-21) and 99dfa6f970
    (sparse-checkout: use in-process update for disable subcommand,
    2019-11-21), but I didn't see anything in their commit messages or
    on the list explaining the strbufs.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/sparse-checkout.c

@@ -442,7 +442,6 @@ static int sparse_checkout_init(int argc, const char **argv, const char *prefix)
 	char *sparse_filename;
 	int res;
 	struct object_id oid;
-	struct strbuf pattern = STRBUF_INIT;
 
 	static struct option builtin_sparse_checkout_init_options[] = {
 		OPT_BOOL(0, "cone", &init_opts.cone_mode,
@@ -493,10 +492,8 @@ static int sparse_checkout_init(int argc, const char **argv, const char *prefix)
 		return 0;
 	}
 
-	strbuf_addstr(&pattern, "/*");
-	add_pattern(strbuf_detach(&pattern, NULL), empty_base, 0, &pl, 0);
-	strbuf_addstr(&pattern, "!/*/");
-	add_pattern(strbuf_detach(&pattern, NULL), empty_base, 0, &pl, 0);
+	add_pattern("/*", empty_base, 0, &pl, 0);
+	add_pattern("!/*/", empty_base, 0, &pl, 0);
 	pl.use_cone_patterns = init_opts.cone_mode;
 
 	return write_patterns_and_update(&pl);
@@ -893,7 +890,6 @@ static int sparse_checkout_disable(int argc, const char **argv,
 		OPT_END(),
 	};
 	struct pattern_list pl;
-	struct strbuf match_all = STRBUF_INIT;
 
 	/*
 	 * We do not exit early if !core_apply_sparse_checkout; due to the
@@ -919,8 +915,7 @@ static int sparse_checkout_disable(int argc, const char **argv,
 	pl.use_cone_patterns = 0;
 	core_apply_sparse_checkout = 1;
 
-	strbuf_addstr(&match_all, "/*");
-	add_pattern(strbuf_detach(&match_all, NULL), empty_base, 0, &pl, 0);
+	add_pattern("/*", empty_base, 0, &pl, 0);
 
 	prepare_repo_settings(the_repository);
 	the_repository->settings.sparse_index = 0;

t/t1090-sparse-checkout-scope.sh

@@ -6,6 +6,7 @@ GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
 TEST_CREATE_REPO_NO_TEMPLATE=1
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 test_expect_success 'setup' '

t/t3602-rm-sparse-checkout.sh

@@ -2,6 +2,7 @@
 
 test_description='git rm in sparse checked out working trees'
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 test_expect_success 'setup' "