Teach 'git merge' and 'git pull' the option --ff-only

PATCH New Björn Gustavsson 1 participant 1 message Jun 15, 2016 Documentation

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Björn Gustavsson

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2016-06-15 22:47 UTC #0 lore raw

PATCH 1/1 Teach 'git merge' and 'git pull' the option --ff-only

For convenience in scripts and aliases, add the option --ff-only to only allow fast-forwards (and up-to-date, despite the name).

Disallow combining --ff-only and --no-ff, since they flatly contradict each other.

Allow all other options to be combined with --ff-only (i.e. do not add any code to handle them specially), including the following options:

* --strategy (one or more): As long as the chosen merge strategy results in up-to-date or fast-forward, the command will succeed.

* --squash: I cannot imagine why anyone would want to squash commits only if fast-forward is possible, but I also see no reason why it should not be allowed.

* --message: The message will always be ignored, but I see no need to explicitly disallow providing a redundant message.

Acknowledgements: I did look at Yuval Kogman's earlier patch (107768 in gmane), mainly as shortcut to find my way in the code, but I did not copy anything directly.

Signed-off-by Björn Gustavsson <[email protected]>

---
Here is a re-roll of my previous patch with improvements suggested by Junio's review. Compared to the previous version, I have changed the following:

* The documentation now clearly states that up-to-date is also allowed.

* The redundant and incorrect test to reject merge strategies that do not allow fast-forward has been removed (along with the corresponding test case).

* I have added some background on the design decisions to the commit message.

* I have added two test cases to test --squash in combination with --ff-only.

 Documentation/merge-options.txt |    5 ++++
 builtin-merge.c                 |   11 +++++++++-
 git-pull.sh                     |    7 ++++-
 t/t7600-merge.sh                |   41 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 61 insertions(+), 3 deletions(-)

Documentation/merge-options.txt +5 -0

index adadf8e..27a9a84 100644
@@ -60,6 +60,11 @@
 	a fast-forward, only update the branch pointer. This is
 	the default behavior of git-merge.
 
+--ff-only::
+	Refuse to merge and exit with a non-zero status unless the
+	current `HEAD` is already up-to-date or the merge can be
+	resolved as a fast-forward.
+
 -s <strategy>::
 --strategy=<strategy>::
 	Use the given merge strategy; can be supplied more than

builtin-merge.c +10 -1

index b6b8428..5e8c4b5 100644
@@ -43,6 +43,7 @@ static const char * const builtin_merge_usage[] = {
 
 static int show_diffstat = 1, option_log, squash;
 static int option_commit = 1, allow_fast_forward = 1;
+static int fast_forward_only;
 static int allow_trivial = 1, have_message;
 static struct strbuf merge_msg;
 static struct commit_list *remoteheads;

@@ -167,6 +168,8 @@ static struct option builtin_merge_options[] = {
 		"perform a commit if the merge succeeds (default)"),
 	OPT_BOOLEAN(0, "ff", &allow_fast_forward,
 		"allow fast forward (default)"),
+	OPT_BOOLEAN(0, "ff-only", &fast_forward_only,
+		"abort if fast forward is not possible"),
 	OPT_CALLBACK('s', "strategy", &use_strategies, "strategy",
 		"merge strategy to use", option_parse_strategy),
 	OPT_CALLBACK('m', "message", &merge_msg, "message",

@@ -874,6 +877,9 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		option_commit = 0;
 	}
 
+	if (!allow_fast_forward && fast_forward_only)
+		die("You cannot combine --no-ff with --ff-only.");
+
 	if (!argc)
 		usage_with_options(builtin_merge_usage,
 			builtin_merge_options);

@@ -1040,7 +1046,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		 * only one common.
 		 */
 		refresh_cache(REFRESH_QUIET);
-		if (allow_trivial) {
+		if (allow_trivial && !fast_forward_only) {
 			/* See if it is really trivial. */
 			git_committer_info(IDENT_ERROR_ON_NO_NAME);
 			printf("Trying really trivial in-index merge...\n");

@@ -1079,6 +1085,9 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		}
 	}
 
+	if (fast_forward_only)
+		die("Not possible to fast forward, aborting.");
+
 	/* We are going to make a new commit. */
 	git_committer_info(IDENT_ERROR_ON_NO_NAME);

git-pull.sh +5 -2

index fc78592..37f3d93 100755
@@ -16,7 +16,8 @@ cd_to_toplevel
 test -z "$(git ls-files -u)" ||
 	die "You are in the middle of a conflicted merge."
 
-strategy_args= diffstat= no_commit= squash= no_ff= log_arg= verbosity=
+strategy_args= diffstat= no_commit= squash= no_ff= ff_only=
+log_arg= verbosity=
 curr_branch=$(git symbolic-ref -q HEAD)
 curr_branch_short=$(echo "$curr_branch" | sed "s|refs/heads/||")
 rebase=$(git config --bool branch.$curr_branch_short.rebase)

@@ -45,6 +46,8 @@ do
 		no_ff=--ff ;;
 	--no-ff)
 		no_ff=--no-ff ;;
+	--ff-only)
+		ff_only=--ff-only ;;
 	-s=*|--s=*|--st=*|--str=*|--stra=*|--strat=*|--strate=*|\
 		--strateg=*|--strategy=*|\
 	-s|--s|--st|--str|--stra|--strat|--strate|--strateg|--strategy)

@@ -215,5 +218,5 @@ merge_name=$(git fmt-merge-msg $log_arg <"$GIT_DIR/FETCH_HEAD") || exit
 test true = "$rebase" &&
 	exec git-rebase $diffstat $strategy_args --onto $merge_head \
 	${oldremoteref:-$merge_head}
-exec git-merge $diffstat $no_commit $squash $no_ff $log_arg $strategy_args \
+exec git-merge $diffstat $no_commit $squash $no_ff $ff_only $log_arg $strategy_args \
 	"$merge_name" HEAD $merge_head $verbosity

t/t7600-merge.sh +41 -0

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