[PATCH v1 0/5] git log: configurable default format for merge diffs

[Sergey Organov <sorganov@gmail.com>]

These patches introduce capability to configure the default format of
output of diffs for merge commits by means of new log.diffMerges
configuration variable. The default format is then used by -m,
--diff-merges=m, and new --diff-merges=default options.

In particular,

  git config log.diffMerges first-parent

will change -m option format from "separate" to "first-parent" that
will in turn cause, say,

  git show -m <merge_commit>

to output diff to the first parent only, instead of appending
typically large and surprising diff to the second parent at the end of
the output.

Updates in v1:

  * Renamed abbreviated value "def" to full "default"

  * Fixed tests to use "test_config" instead of "git config"

  * Meld all "git config" changes into single commit that includes
    code, documentation, and tests, as they are mutually
    interdependent.

Sergey Organov (5):
  diff-merges: introduce --diff-merges=default
  diff-merges: refactor set_diff_merges()
  diff-merges: adapt -m to enable default diff format
  diff-merges: introduce log.diffMerges config variable
  doc/diff-options: document new --diff-merges features

 Documentation/config/log.txt   |  5 +++
 Documentation/diff-options.txt | 15 ++++++---
 builtin/log.c                  |  2 ++
 diff-merges.c                  | 58 ++++++++++++++++++++++++----------
 diff-merges.h                  |  2 ++
 t/t4013-diff-various.sh        | 31 ++++++++++++++++++
 t/t9902-completion.sh          |  3 ++
 7 files changed, 95 insertions(+), 21 deletions(-)

Interdiff against v0:
diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index 09b07231b5a4..31e2bacf5252 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -34,7 +34,7 @@ endif::git-diff[]
 endif::git-format-patch[]
 
 ifdef::git-log[]
---diff-merges=(off|none|def|first-parent|1|separate|m|combined|c|dense-combined|cc)::
+--diff-merges=(off|none|default|first-parent|1|separate|m|combined|c|dense-combined|cc)::
 --no-diff-merges::
 	Specify diff format to be used for merge commits. Default is
 	{diff-merges-default} unless `--first-parent` is in use, in which case
@@ -45,7 +45,7 @@ ifdef::git-log[]
 	Disable output of diffs for merge commits. Useful to override
 	implied value.
 +
---diff-merges=def:::
+--diff-merges=default:::
 --diff-merges=m:::
 -m:::
 	This option makes diff output for merge commits to be shown in
diff --git a/diff-merges.c b/diff-merges.c
index f68e4376fd63..75630fb8e6b8 100644
--- a/diff-merges.c
+++ b/diff-merges.c
@@ -67,7 +67,7 @@ static diff_merges_setup_func_t func_by_opt(const char *optarg)
 		return set_combined;
 	else if (!strcmp(optarg, "cc") || !strcmp(optarg, "dense-combined"))
 		return set_dense_combined;
-	else if (!strcmp(optarg, "m") || !strcmp(optarg, "def"))
+	else if (!strcmp(optarg, "m") || !strcmp(optarg, "default"))
 		return set_to_default;
 	return NULL;
 }
diff --git a/t/t4013-diff-various.sh b/t/t4013-diff-various.sh
index ee4afca06ced..87cab7867135 100755
--- a/t/t4013-diff-various.sh
+++ b/t/t4013-diff-various.sh
@@ -452,37 +452,34 @@ diff-tree --stat --compact-summary initial mode
 diff-tree -R --stat --compact-summary initial mode
 EOF
 
-test_expect_success 'log --diff-merges=def matches --diff-merges=separate' '
+test_expect_success 'log --diff-merges=default matches --diff-merges=separate' '
 	git log -p --diff-merges=separate master >result &&
 	process_diffs result >expected &&
-	git log -p --diff-merges=def master >result &&
+	git log -p --diff-merges=default master >result &&
 	process_diffs result >actual &&
 	test_cmp expected actual
 '
 
 test_expect_success 'deny wrong log.diffMerges config' '
-	git config log.diffMerges wrong-value &&
-	test_expect_code 128 git log &&
-	git config --unset log.diffMerges
+	test_config log.diffMerges wrong-value &&
+	test_expect_code 128 git log
 '
 
 test_expect_success 'git config log.diffMerges first-parent' '
 	git log -p --diff-merges=first-parent master >result &&
 	process_diffs result >expected &&
-	git config log.diffMerges first-parent &&
-	git log -p --diff-merges=def master >result &&
+	test_config log.diffMerges first-parent &&
+	git log -p --diff-merges=default master >result &&
 	process_diffs result >actual &&
-	git config --unset log.diffMerges &&
 	test_cmp expected actual
 '
 
 test_expect_success 'git config log.diffMerges first-parent vs -m' '
 	git log -p --diff-merges=first-parent master >result &&
 	process_diffs result >expected &&
-	git config log.diffMerges first-parent &&
+	test_config log.diffMerges first-parent &&
 	git log -p -m master >result &&
 	process_diffs result >actual &&
-	git config --unset log.diffMerges &&
 	test_cmp expected actual
 '
 
-- 
2.25.1