Merge branch 'rn/sparse-describe'

"git describe --dirty" learns to work better with sparse-index.

* rn/sparse-describe:
  describe: enable sparse index for describe

builtin/describe.c

@@ -658,6 +658,8 @@ int cmd_describe(int argc, const char **argv, const char *prefix)
 			int fd, result;
 
 			setup_work_tree();
+			prepare_repo_settings(the_repository);
+			the_repository->settings.command_requires_full_index = 0;
 			repo_read_index(the_repository);
 			refresh_index(&the_index, REFRESH_QUIET|REFRESH_UNMERGED,
 				      NULL, NULL, NULL);

t/perf/p2000-sparse-operations.sh

@@ -43,6 +43,7 @@ test_expect_success 'setup repo and indexes' '
 	done &&
 
 	git sparse-checkout init --cone &&
+	git tag -a v1.0 -m "Final" &&
 	git sparse-checkout set $SPARSE_CONE &&
 	git checkout -b wide $OLD_COMMIT &&
 
@@ -126,5 +127,7 @@ test_perf_on_all git update-index --add --remove $SPARSE_CONE/a
 test_perf_on_all "git rm -f $SPARSE_CONE/a && git checkout HEAD -- $SPARSE_CONE/a"
 test_perf_on_all git grep --cached bogus -- "f2/f1/f1/*"
 test_perf_on_all git write-tree
+test_perf_on_all git describe --dirty
+test_perf_on_all 'echo >>new && git describe --dirty'
 
 test_done

t/t1092-sparse-checkout-compatibility.sh

@@ -1514,6 +1514,31 @@ test_expect_success 'sparse-index is not expanded: stash' '
 	ensure_not_expanded stash pop
 '
 
+test_expect_success 'describe tested on all' '
+	init_repos &&
+
+	# Add tag to be read by describe
+
+	run_on_all git tag -a v1.0 -m "Version 1" &&
+	test_all_match git describe --dirty &&
+	run_on_all rm g &&
+	test_all_match git describe --dirty
+'
+
+
+test_expect_success 'sparse-index is not expanded: describe' '
+	init_repos &&
+
+	# Add tag to be read by describe
+
+	git -C sparse-index tag -a v1.0 -m "Version 1" &&
+
+	ensure_not_expanded describe --dirty &&
+	echo "test" >>sparse-index/g &&
+	ensure_not_expanded describe --dirty &&
+	ensure_not_expanded describe
+'
+
 test_expect_success 'sparse index is not expanded: diff' '
 	init_repos &&