[PATCH v5] Add default merge options for all branches

[Michael Grubb <devel@dailyvoid.com>]

Add merge.ff flag to support turning off fast-forward merges by default.
This flag is overridden if any branch.x.mergeoptions turn it back on.

 Documentation/merge-config.txt |    6 ++++++
 builtin/merge.c                |    3 +++
 2 files changed, 9 insertions(+), 0 deletions(-)

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Reported-by: Michael Grubb <devel@dailyvoid.com>
---
 Documentation/merge-config.txt |    6 ++++++
 builtin/merge.c                |    3 +++
 t/t7600-merge.sh               |   23 +++++++++++++++++++++++
 3 files changed, 32 insertions(+), 0 deletions(-)

diff --git a/Documentation/merge-config.txt b/Documentation/merge-config.txt
index 8920258..2aa4408 100644
--- a/Documentation/merge-config.txt
+++ b/Documentation/merge-config.txt
@@ -16,6 +16,12 @@ merge.defaultToUpstream::
 	to their corresponding remote tracking branches, and the tips of
 	these tracking branches are merged.
 
+merge.ff::
+	Do not generate a merge commit if the merge resolved as a
+	fast-forward; only update the branch pointer instead.  Setting
+	this to `false` would be equivalent to giving `--no-ff` from
+	the command line.
+
 merge.log::
 	In addition to branch names, populate the log message with at
 	most the specified number of one-line descriptions from the
diff --git a/builtin/merge.c b/builtin/merge.c
index d171c63..5194f04 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -541,6 +541,9 @@ static int git_merge_config(const char *k, const char *v, void *cb)
 		if (is_bool && shortlog_len)
 			shortlog_len = DEFAULT_MERGE_LOG_LEN;
 		return 0;
+	} else if (!strcmp(k, "merge.ff")) {
+		allow_fast_forward = git_config_bool(k, v);
+		return 0;
 	} else if (!strcmp(k, "merge.defaulttoupstream")) {
 		default_to_upstream = git_config_bool(k, v);
 		return 0;
diff --git a/t/t7600-merge.sh b/t/t7600-merge.sh
index e84e822..21c25d4 100755
--- a/t/t7600-merge.sh
+++ b/t/t7600-merge.sh
@@ -415,6 +415,29 @@ test_expect_success 'merge c0 with c1 (no-ff)' '
 
 test_debug 'git log --graph --decorate --oneline --all'
 
+test_expect_success 'merge c0 with c1 (merge.ff=false)' '
+	git reset --hard c0 &&
+	git config merge.ff false &&
+	test_tick &&
+	git merge c1 &&
+	git config --remove-section merge &&
+	verify_merge file result.1 &&
+	verify_parents $c0 $c1
+'
+test_debug 'git log --graph --decorate --oneline --all'
+
+test_expect_success 'combine branch.master.mergeoptions with merge.ff' '
+	git reset --hard c0 &&
+	git config branch.master.mergeoptions --ff
+	git config merge.ff false
+	test_tick &&
+	git merge c1 &&
+	git config --remove-section "branch.master" &&
+	git config --remove-section "merge" &&
+	verify_merge file result.1 &&
+	verify_parents "$c0"
+'
+
 test_expect_success 'combining --squash and --no-ff is refused' '
 	test_must_fail git merge --squash --no-ff c1 &&
 	test_must_fail git merge --no-ff --squash c1