Merge branch 'so/diff-merges-dd'

"git log" and friends learned "--dd" that is a short-hand for
"--diff-merges=first-parent -p".

* so/diff-merges-dd:
  completion: complete '--dd'
  diff-merges: introduce '--dd' option
  diff-merges: improve --diff-merges documentation

5 files changed, 73 insertions, 49 deletions

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index 35fae7c87c..ac6bc53d8e 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -37,66 +37,79 @@ endif::git-diff[]
 endif::git-format-patch[]
 
 ifdef::git-log[]
---diff-merges=(off|none|on|first-parent|1|separate|m|combined|c|dense-combined|cc|remerge|r)::
+-m::
+	Show diffs for merge commits in the default format. This is
+	similar to '--diff-merges=on', except `-m` will
+	produce no output unless `-p` is given as well.
+
+-c::
+	Produce combined diff output for merge commits.
+	Shortcut for '--diff-merges=combined -p'.
+
+--cc::
+	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 remerge-diff output for merge commits.
+	Shortcut for '--diff-merges=remerge -p'.
+
 --no-diff-merges::
+	Synonym for '--diff-merges=off'.
+
+--diff-merges=<format>::
 	Specify diff format to be used for merge commits. Default is
-	{diff-merges-default} unless `--first-parent` is in use, in which case
-	`first-parent` is the default.
+	{diff-merges-default} unless `--first-parent` is in use, in
+	which case `first-parent` is the default.
 +
---diff-merges=(off|none):::
---no-diff-merges:::
+The following formats are supported:
++
+--
+off, none::
 	Disable output of diffs for merge commits. Useful to override
 	implied value.
 +
---diff-merges=on:::
---diff-merges=m:::
--m:::
-	This option makes diff output for merge commits to be shown in
-	the default format. `-m` will produce the output only if `-p`
-	is given as well. The default format could be changed using
-	`log.diffMerges` configuration parameter, which default value
+on, m::
+	Make diff output for merge commits to be shown in the default
+	format. The default format could be changed using
+	`log.diffMerges` configuration variable, whose default value
 	is `separate`.
 +
---diff-merges=first-parent:::
---diff-merges=1:::
-	This option makes merge commits show the full diff with
-	respect to the first parent only.
+first-parent, 1::
+	Show full diff with respect to first parent. This is the same
+	format as `--patch` produces for non-merge commits.
++
+separate::
+	Show full diff with respect to each of parents.
+	Separate log entry and diff is generated for each parent.
 +
---diff-merges=separate:::
-	This makes merge commits show the full diff with respect to
-	each of the parents. Separate log entry and diff is generated
-	for each parent.
+combined, c::
+	Show differences from each of the parents to the merge
+	result simultaneously instead of showing pairwise diff between
+	a parent and the result one at a time. Furthermore, it lists
+	only files which were modified from all parents.
 +
---diff-merges=remerge:::
---diff-merges=r:::
---remerge-diff:::
-	With this option, two-parent merge commits are remerged to
-	create a temporary tree object -- potentially containing files
-	with conflict markers and such.  A diff is then shown between
-	that temporary tree and the actual merge commit.
+dense-combined, cc::
+	Further compress output produced by `--diff-merges=combined`
+	by omitting uninteresting hunks whose contents in the parents
+	have only two variants and the merge result picks one of them
+	without modification.
++
+remerge, r::
+	Remerge two-parent merge commits to create a temporary tree
+	object--potentially containing files with conflict markers
+	and such.  A diff is then shown between that temporary tree
+	and the actual merge commit.
 +
 The output emitted when this option is used is subject to change, and
 so is its interaction with other options (unless explicitly
 documented).
-+
---diff-merges=combined:::
---diff-merges=c:::
--c:::
-	With this option, diff output for a merge commit shows the
-	differences from each of the parents to the merge result
-	simultaneously instead of showing pairwise diff between a
-	parent and the result one at a time. Furthermore, it lists
-	only files which were modified from all parents. `-c` implies
-	`-p`.
-+
---diff-merges=dense-combined:::
---diff-merges=cc:::
---cc:::
-	With this option the output produced by
-	`--diff-merges=combined` is further compressed by omitting
-	uninteresting hunks whose contents in the parents have only
-	two variants and the merge result picks one of them without
-	modification.  `--cc` implies `-p`.
+--
 
 --combined-all-paths::
 	This flag causes combined diffs (used for merge commits) to
diff --git a/Documentation/git-log.txt b/Documentation/git-log.txt
index 2a66cf8880..579682172f 100644
--- a/Documentation/git-log.txt
+++ b/Documentation/git-log.txt
@@ -120,11 +120,11 @@ 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
-the default format.
+the default format for merge commits.
 
 :git-log: 1
 :diff-merges-default: `off`
diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index 477ef8157a..13a39ebd2e 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -2053,7 +2053,7 @@ __git_log_shortlog_options="
 "
 # Options accepted by log and show
 __git_log_show_options="
-	--diff-merges --diff-merges= --no-diff-merges --remerge-diff
+	--diff-merges --diff-merges= --no-diff-merges --dd --remerge-diff
 "
 
 __git_diff_merges_opts="off none on first-parent 1 separate m combined c dense-combined cc remerge r"
diff --git a/diff-merges.c b/diff-merges.c
index ec97616db1..45507588a2 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 5de1d19075..4b47480831 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