[PATCH v3 2/3] diff-merges: introduce '--dd' 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".

NOTE: originally proposed as '-d', and renamed to '--dd' due to Junio
request to keep "short-and-sweet" '-d' reserved for other uses.

Signed-off-by: Sergey Organov <sorganov@gmail.com>
---
 Documentation/diff-options.txt | 5 +++++
 Documentation/git-log.txt      | 2 +-
 diff-merges.c                  | 3 +++
 t/t4013-diff-various.sh        | 8 ++++++++
 4 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index 8035210c1418..f80d493dd4c8 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -56,6 +56,11 @@ ifdef::git-log[]
 	Produce dense combined diff output for merge commits.
 	Shortcut for '--diff-merges=dense-combined -p'.
 
+--dd::
+	Produce diff with respect to first parent for both merge and
+	regular commits.
+	Shortcut for '--diff-merges=first-parent -p'.
+
 --remerge-diff::
 	Produce diff against re-merge.
 	Shortcut for '--diff-merges=remerge -p'.
diff --git a/Documentation/git-log.txt b/Documentation/git-log.txt
index 9b7ec96e767a..579682172fe4 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
+`-m`, `-c`, `--cc`, and `--dd` 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..45507588a279 100644
--- a/diff-merges.c
+++ b/diff-merges.c
@@ -131,6 +131,9 @@ int diff_merges_parse_opts(struct rev_info *revs, const char **argv)
 	} else if (!strcmp(arg, "--cc")) {
 		set_dense_combined(revs);
 		revs->merges_imply_patch = 1;
+	} else if (!strcmp(arg, "--dd")) {
+		set_first_parent(revs);
+		revs->merges_imply_patch = 1;
 	} else if (!strcmp(arg, "--remerge-diff")) {
 		set_remerge_diff(revs);
 		revs->merges_imply_patch = 1;
diff --git a/t/t4013-diff-various.sh b/t/t4013-diff-various.sh
index 5de1d190759f..4b474808311e 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 --dd matches --diff-merges=1 -p' '
+	git log --diff-merges=1 -p master >result &&
+	process_diffs result >expected &&
+	git log --dd 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