[PATCH 2/2] diff-merges: introduce '-d' option

[Sergey Organov <sorganov@gmail.com>]

This option provides a shortcut to request diff with respect to first
parent for any kind of commit, universally. It's implemented as pure
synonym for "--diff-merges=first-parent --patch".

Signed-off-by: Sergey Organov <sorganov@gmail.com>
---
 Documentation/diff-options.txt | 4 ++++
 Documentation/git-log.txt      | 2 +-
 diff-merges.c                  | 3 +++
 t/t4013-diff-various.sh        | 8 ++++++++
 4 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index f93aa3e46a52..d773dafcb10a 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -51,6 +51,10 @@ ifdef::git-log[]
 Note: This option not implying `-p` is legacy feature that is
 preserved for the sake of backward compatibility.
 
+-d::
+	Produce diff with respect to first parent.
+	Shortcut for '--diff-merges=first-parent -p'.
+
 -c::
 	Produce combined diff output for merge commits.
 	Shortcut for '--diff-merges=combined -p'.
diff --git a/Documentation/git-log.txt b/Documentation/git-log.txt
index 9b7ec96e767a..59bd74a1a596 100644
--- a/Documentation/git-log.txt
+++ b/Documentation/git-log.txt
@@ -120,7 +120,7 @@ By default, `git log` does not generate any diff output. The options
 below can be used to show the changes made by each commit.
 
 Note that unless one of `--diff-merges` variants (including short
-`-m`, `-c`, and `--cc` options) is explicitly given, merge commits
+`-d`, `-m`, `-c`, and `--cc` options) is explicitly given, merge commits
 will not show a diff, even if a diff format like `--patch` is
 selected, nor will they match search options like `-S`. The exception
 is when `--first-parent` is in use, in which case `first-parent` is
diff --git a/diff-merges.c b/diff-merges.c
index ec97616db1df..6eb72e6fc28a 100644
--- a/diff-merges.c
+++ b/diff-merges.c
@@ -125,6 +125,9 @@ int diff_merges_parse_opts(struct rev_info *revs, const char **argv)
 	if (!suppress_m_parsing && !strcmp(arg, "-m")) {
 		set_to_default(revs);
 		revs->merges_need_diff = 0;
+	} else if (!strcmp(arg, "-d")) {
+		set_first_parent(revs);
+		revs->merges_imply_patch = 1;
 	} else if (!strcmp(arg, "-c")) {
 		set_combined(revs);
 		revs->merges_imply_patch = 1;
diff --git a/t/t4013-diff-various.sh b/t/t4013-diff-various.sh
index 5de1d190759f..a07d6eb6dd97 100755
--- a/t/t4013-diff-various.sh
+++ b/t/t4013-diff-various.sh
@@ -473,6 +473,14 @@ test_expect_success 'log --diff-merges=on matches --diff-merges=separate' '
 	test_cmp expected actual
 '
 
+test_expect_success 'log -d matches --diff-merges=1 -p' '
+	git log --diff-merges=1 -p master >result &&
+	process_diffs result >expected &&
+	git log -d master >result &&
+	process_diffs result >actual &&
+	test_cmp expected actual
+'
+
 test_expect_success 'deny wrong log.diffMerges config' '
 	test_config log.diffMerges wrong-value &&
 	test_expect_code 128 git log
-- 
2.25.1