[PATCH v7 2/2] diff-files: integrate with sparse index

[Shuqi Liang <cheskaqiqi@gmail.com>]

Originally, diff-files a pathspec that is out-of-cone in a sparse-index
environment, Git dies with "pathspec '<x>' did not match any files",
mainly because it does not expand the index so nothing is matched.
Expand the index when the <pathspec> needs an expanded index, i.e. the
<pathspec> contains wildcard that may need a full-index or the
<pathspec> is simply outside of sparse-checkout definition.

Remove full index requirement for `git diff-files`.Create an
'ensure_expanded' to handle silent failures. Add test to
ensure the index only expanded when necessary in `git diff-files`.

The `p2000` tests demonstrate a ~96% execution time reduction for 'git
diff-files' and a ~97% execution time reduction for 'git diff-files'
for a file using a sparse index:

Test                                           before  after
-----------------------------------------------------------------
2000.78: git diff-files (full-v3)              0.09    0.08 -11.1%
2000.79: git diff-files (full-v4)              0.09    0.09 +0.0%
2000.80: git diff-files (sparse-v3)            0.52    0.02 -96.2%
2000.81: git diff-files (sparse-v4)            0.51    0.02 -96.1%
2000.82: git diff-files f2/f4/a (full-v3)      0.06    0.07 +16.7%
2000.83: git diff-files f2/f4/a (full-v4)      0.08    0.08 +0.0%
2000.84: git diff-files f2/f4/a (sparse-v3)    0.46    0.01 -97.8%
2000.85: git diff-files f2/f4/a (sparse-v4)    0.51    0.02 -96.1%

Signed-off-by: Shuqi Liang <cheskaqiqi@gmail.com>
---
 builtin/diff-files.c                     |  8 ++++
 t/perf/p2000-sparse-operations.sh        |  2 +
 t/t1092-sparse-checkout-compatibility.sh | 52 ++++++++++++++++++++++++
 3 files changed, 62 insertions(+)

diff --git a/builtin/diff-files.c b/builtin/diff-files.c
index dc991f753b..db90592090 100644
--- a/builtin/diff-files.c
+++ b/builtin/diff-files.c
@@ -27,6 +27,10 @@ int cmd_diff_files(int argc, const char **argv, const char *prefix)
 		usage(diff_files_usage);
 
 	git_config(git_diff_basic_config, NULL); /* no "diff" UI options */
+
+	prepare_repo_settings(the_repository);
+	the_repository->settings.command_requires_full_index = 0;
+
 	repo_init_revisions(the_repository, &rev, prefix);
 	rev.abbrev = 0;
 
@@ -80,6 +84,10 @@ int cmd_diff_files(int argc, const char **argv, const char *prefix)
 		result = -1;
 		goto cleanup;
 	}
+
+	if (pathspec_needs_expanded_index(the_repository->index, &rev.diffopt.pathspec))
+		ensure_full_index(the_repository->index);
+
 	result = run_diff_files(&rev, options);
 	result = diff_result_code(&rev.diffopt, result);
 cleanup:
diff --git a/t/perf/p2000-sparse-operations.sh b/t/perf/p2000-sparse-operations.sh
index 3242cfe91a..82751f2ca3 100755
--- a/t/perf/p2000-sparse-operations.sh
+++ b/t/perf/p2000-sparse-operations.sh
@@ -125,5 +125,7 @@ test_perf_on_all git checkout-index -f --all
 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 --sparse bogus -- "f2/f1/f1/*"
+test_perf_on_all git diff-files
+test_perf_on_all git diff-files $SPARSE_CONE/a
 
 test_done
diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index d23041e27a..152f3f752e 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh
@@ -1401,6 +1401,30 @@ ensure_not_expanded () {
 	test_region ! index ensure_full_index trace2.txt
 }
 
+ensure_expanded () {
+	rm -f trace2.txt &&
+	if test -z "$WITHOUT_UNTRACKED_TXT"
+	then
+		echo >>sparse-index/untracked.txt
+	fi &&
+
+	if test "$1" = "!"
+	then
+		shift &&
+		test_must_fail env \
+			GIT_TRACE2_EVENT="$(pwd)/trace2.txt" \
+			git -C sparse-index "$@" \
+			>sparse-index-out \
+			2>sparse-index-error || return 1
+	else
+		GIT_TRACE2_EVENT="$(pwd)/trace2.txt" \
+			git -C sparse-index "$@" \
+			>sparse-index-out \
+			2>sparse-index-error || return 1
+	fi &&
+	test_region index ensure_full_index trace2.txt
+}
+
 test_expect_success 'sparse-index is not expanded' '
 	init_repos &&
 
@@ -2101,4 +2125,32 @@ test_expect_success 'diff-files with pathspec outside sparse definition' '
 	test_all_match git diff-files "folder*/a" 
 '
 
+test_expect_success 'diff-files pathspec expands index when necessary' '
+	init_repos &&
+
+	write_script edit-contents <<-\EOF &&
+	echo text >>"$1"
+	EOF
+
+	run_on_all ../edit-contents deep/a &&
+	
+	# pathspec that should expand index
+	ensure_expanded diff-files "*/a" &&
+	ensure_expanded diff-files "**a" 
+'
+
+test_expect_success 'sparse index is not expanded: diff-files' '
+	init_repos &&
+
+	write_script edit-contents <<-\EOF &&
+	echo text >>"$1"
+	EOF
+
+	run_on_all ../edit-contents deep/a &&
+
+	ensure_not_expanded diff-files &&
+	ensure_not_expanded diff-files deep/a &&
+	ensure_not_expanded diff-files deep/*
+'
+
 test_done
-- 
2.39.0