Merge branch 'en/pull-conflicting-options'

"git pull" had various corner cases that were not well thought out
around its --rebase backend, e.g. "git pull --ff-only" did not stop
but went ahead and rebased when the history on other side is not a
descendant of our history.  The series tries to fix them up.

* en/pull-conflicting-options:
  pull: fix handling of multiple heads
  pull: update docs & code for option compatibility with rebasing
  pull: abort by default when fast-forwarding is not possible
  pull: make --rebase and --no-rebase override pull.ff=only
  pull: since --ff-only overrides, handle it first
  pull: abort if --ff-only is given and fast-forwarding is impossible
  t7601: add tests of interactions with multiple merge heads and config
  t7601: test interaction of merge/rebase/fast-forward flags and options

Documentation/git-merge.txt

@@ -61,6 +61,8 @@ merge has resulted in conflicts.
 
 OPTIONS
 -------
+:git-merge: 1
+
 include::merge-options.txt[]
 
 -m <msg>::

Documentation/git-pull.txt

@@ -15,14 +15,17 @@ SYNOPSIS
 DESCRIPTION
 -----------
 
-Incorporates changes from a remote repository into the current
-branch.  In its default mode, `git pull` is shorthand for
-`git fetch` followed by `git merge FETCH_HEAD`.
+Incorporates changes from a remote repository into the current branch.
+If the current branch is behind the remote, then by default it will
+fast-forward the current branch to match the remote.  If the current
+branch and the remote have diverged, the user needs to specify how to
+reconcile the divergent branches with `--rebase` or `--no-rebase` (or
+the corresponding configuration option in `pull.rebase`).
 
-More precisely, 'git pull' runs 'git fetch' with the given
-parameters and calls 'git merge' to merge the retrieved branch
-heads into the current branch.
-With `--rebase`, it runs 'git rebase' instead of 'git merge'.
+More precisely, `git pull` runs `git fetch` with the given parameters
+and then depending on configuration options or command line flags,
+will call either `git rebase` or `git merge` to reconcile diverging
+branches.
 
 <repository> should be the name of a remote repository as
 passed to linkgit:git-fetch[1].  <refspec> can name an
@@ -132,7 +135,7 @@ published that history already.  Do *not* use this option
 unless you have read linkgit:git-rebase[1] carefully.
 
 --no-rebase::
-	Override earlier --rebase.
+	This is shorthand for --rebase=false.
 
 Options related to fetching
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~

Documentation/merge-options.txt

@@ -2,6 +2,9 @@
 --no-commit::
 	Perform the merge and commit the result. This option can
 	be used to override --no-commit.
+ifdef::git-pull[]
+	Only useful when merging.
+endif::git-pull[]
 +
 With --no-commit perform the merge and stop just before creating
 a merge commit, to give the user a chance to inspect and further
@@ -39,6 +42,7 @@ set to `no` at the beginning of them.
 	to `MERGE_MSG` before being passed on to the commit machinery in the
 	case of a merge conflict.
 
+ifdef::git-merge[]
 --ff::
 --no-ff::
 --ff-only::
@@ -47,6 +51,22 @@ set to `no` at the beginning of them.
 	default unless merging an annotated (and possibly signed) tag
 	that is not stored in its natural place in the `refs/tags/`
 	hierarchy, in which case `--no-ff` is assumed.
+endif::git-merge[]
+ifdef::git-pull[]
+--ff-only::
+	Only update to the new history if there is no divergent local
+	history.  This is the default when no method for reconciling
+	divergent histories is provided (via the --rebase=* flags).
+
+--ff::
+--no-ff::
+	When merging rather than rebasing, specifies how a merge is
+	handled when the merged-in history is already a descendant of
+	the current history.  If merging is requested, `--ff` is the
+	default unless merging an annotated (and possibly signed) tag
+	that is not stored in its natural place in the `refs/tags/`
+	hierarchy, in which case `--no-ff` is assumed.
+endif::git-pull[]
 +
 With `--ff`, when possible resolve the merge as a fast-forward (only
 update the branch pointer to match the merged branch; do not create a
@@ -55,9 +75,11 @@ descendant of the current history), create a merge commit.
 +
 With `--no-ff`, create a merge commit in all cases, even when the merge
 could instead be resolved as a fast-forward.
+ifdef::git-merge[]
 +
 With `--ff-only`, resolve the merge as a fast-forward when possible.
 When not possible, refuse to merge and exit with a non-zero status.
+endif::git-merge[]
 
 -S[<keyid>]::
 --gpg-sign[=<keyid>]::
@@ -73,6 +95,9 @@ When not possible, refuse to merge and exit with a non-zero status.
 	In addition to branch names, populate the log message with
 	one-line descriptions from at most <n> actual commits that are being
 	merged. See also linkgit:git-fmt-merge-msg[1].
+ifdef::git-pull[]
+	Only useful when merging.
+endif::git-pull[]
 +
 With --no-log do not list one-line descriptions from the
 actual commits being merged.
@@ -102,10 +127,17 @@ With --no-squash perform the merge and commit the result. This
 option can be used to override --squash.
 +
 With --squash, --commit is not allowed, and will fail.
+ifdef::git-pull[]
++
+Only useful when merging.
+endif::git-pull[]
 
 --no-verify::
 	This option bypasses the pre-merge and commit-msg hooks.
 	See also linkgit:githooks[5].
+ifdef::git-pull[]
+	Only useful when merging.
+endif::git-pull[]
 
 -s <strategy>::
 --strategy=<strategy>::
@@ -127,6 +159,10 @@ With --squash, --commit is not allowed, and will fail.
 	default trust model, this means the signing key has been signed by
 	a trusted key.  If the tip commit of the side branch is not signed
 	with a valid key, the merge is aborted.
+ifdef::git-pull[]
++
+Only useful when merging.
+endif::git-pull[]
 
 --summary::
 --no-summary::
@@ -167,3 +203,7 @@ endif::git-pull[]
 	projects that started their lives independently. As that is
 	a very rare occasion, no configuration variable to enable
 	this by default exists and will not be added.
+ifdef::git-pull[]
++
+Only useful when merging.
+endif::git-pull[]

advice.c

@@ -286,6 +286,11 @@ void NORETURN die_conclude_merge(void)
 	die(_("Exiting because of unfinished merge."));
 }
 
+void NORETURN die_ff_impossible(void)
+{
+	die(_("Not possible to fast-forward, aborting."));
+}
+
 void advise_on_updating_sparse_paths(struct string_list *pathspec_list)
 {
 	struct string_list_item *item;

advice.h

@@ -96,6 +96,7 @@ void advise_if_enabled(enum advice_type type, const char *advice, ...);
 int error_resolve_conflict(const char *me);
 void NORETURN die_resolve_conflict(const char *me);
 void NORETURN die_conclude_merge(void);
+void NORETURN die_ff_impossible(void);
 void advise_on_updating_sparse_paths(struct string_list *pathspec_list);
 void detach_advice(const char *new_name);
 

builtin/merge.c

@@ -1622,7 +1622,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 	}
 
 	if (fast_forward == FF_ONLY)
-		die(_("Not possible to fast-forward, aborting."));
+		die_ff_impossible();
 
 	if (autostash)
 		create_autostash(the_repository,

builtin/pull.c

@@ -893,6 +893,8 @@ static int run_rebase(const struct object_id *newbase,
 	strvec_pushv(&args, opt_strategy_opts.v);
 	if (opt_gpg_sign)
 		strvec_push(&args, opt_gpg_sign);
+	if (opt_signoff)
+		strvec_push(&args, opt_signoff);
 	if (opt_autostash == 0)
 		strvec_push(&args, "--no-autostash");
 	else if (opt_autostash == 1)
@@ -911,12 +913,18 @@ static int run_rebase(const struct object_id *newbase,
 	return ret;
 }
 
-static int get_can_ff(struct object_id *orig_head, struct object_id *orig_merge_head)
+static int get_can_ff(struct object_id *orig_head,
+		      struct oid_array *merge_heads)
 {
 	int ret;
 	struct commit_list *list = NULL;
 	struct commit *merge_head, *head;
+	struct object_id *orig_merge_head;
 
+	if (merge_heads->nr > 1)
+		return 0;
+
+	orig_merge_head = &merge_heads->oid[0];
 	head = lookup_commit_reference(the_repository, orig_head);
 	commit_list_insert(head, &list);
 	merge_head = lookup_commit_reference(the_repository, orig_merge_head);
@@ -927,9 +935,9 @@ static int get_can_ff(struct object_id *orig_head, struct object_id *orig_merge_
 
 static void show_advice_pull_non_ff(void)
 {
-	advise(_("Pulling without specifying how to reconcile divergent branches is\n"
-		 "discouraged. You can squelch this message by running one of the following\n"
-		 "commands sometime before your next pull:\n"
+	advise(_("You have divergent branches and need to specify how to reconcile them.\n"
+		 "You can do so by running one of the following commands sometime before\n"
+		 "your next pull:\n"
 		 "\n"
 		 "  git config pull.rebase false  # merge (the default strategy)\n"
 		 "  git config pull.rebase true   # rebase\n"
@@ -966,8 +974,22 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 
 	parse_repo_refspecs(argc, argv, &repo, &refspecs);
 
-	if (!opt_ff)
+	if (!opt_ff) {
 		opt_ff = xstrdup_or_null(config_get_ff());
+		/*
+		 * A subtle point: opt_ff was set on the line above via
+		 * reading from config.  opt_rebase, in contrast, is set
+		 * before this point via command line options.  The setting
+		 * of opt_rebase via reading from config (using
+		 * config_get_rebase()) does not happen until later.  We
+		 * are relying on the next if-condition happening before
+		 * the config_get_rebase() call so that an explicit
+		 * "--rebase" can override a config setting of
+		 * pull.ff=only.
+		 */
+		if (opt_rebase >= 0 && opt_ff && !strcmp(opt_ff, "--ff-only"))
+			opt_ff = "--ff";
+	}
 
 	if (opt_rebase < 0)
 		opt_rebase = config_get_rebase(&rebase_unspecified);
@@ -1041,14 +1063,25 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 			die(_("Cannot merge multiple branches into empty head."));
 		return pull_into_void(merge_heads.oid, &curr_head);
 	}
-	if (opt_rebase && merge_heads.nr > 1)
+	if (merge_heads.nr > 1) {
+		if (opt_rebase)
 			die(_("Cannot rebase onto multiple branches."));
+		if (opt_ff && !strcmp(opt_ff, "--ff-only"))
+			die(_("Cannot fast-forward to multiple branches."));
+	}
 
-	can_ff = get_can_ff(&orig_head, &merge_heads.oid[0]);
+	can_ff = get_can_ff(&orig_head, &merge_heads);
 
-	if (rebase_unspecified && !opt_ff && !can_ff) {
-		if (opt_verbosity >= 0)
+	/* ff-only takes precedence over rebase */
+	if (opt_ff && !strcmp(opt_ff, "--ff-only")) {
+		if (!can_ff)
+			die_ff_impossible();
+		opt_rebase = REBASE_FALSE;
+	}
+	/* If no action specified and we can't fast forward, then warn. */
+	if (!opt_ff && rebase_unspecified && !can_ff) {
 		show_advice_pull_non_ff();
+		die(_("Need to specify how to reconcile divergent branches."));
 	}
 
 	if (opt_rebase) {

t/t4013-diff-various.sh

@@ -65,7 +65,7 @@ test_expect_success setup '
 	export GIT_AUTHOR_DATE GIT_COMMITTER_DATE &&
 
 	git checkout master &&
-	git pull -s ours . side &&
+	git pull -s ours --no-rebase . side &&
 
 	GIT_AUTHOR_DATE="2006-06-26 00:05:00 +0000" &&
 	GIT_COMMITTER_DATE="2006-06-26 00:05:00 +0000" &&

t/t5520-pull.sh

@@ -136,12 +136,12 @@ test_expect_success 'the default remote . should not break explicit pull' '
 	git reset --hard HEAD^ &&
 	echo file >expect &&
 	test_cmp expect file &&
-	git pull . second &&
+	git pull --no-rebase . second &&
 	echo modified >expect &&
 	test_cmp expect file &&
 	git reflog -1 >reflog.actual &&
 	sed "s/^[0-9a-f][0-9a-f]*/OBJID/" reflog.actual >reflog.fuzzy &&
-	echo "OBJID HEAD@{0}: pull . second: Fast-forward" >reflog.expected &&
+	echo "OBJID HEAD@{0}: pull --no-rebase . second: Fast-forward" >reflog.expected &&
 	test_cmp reflog.expected reflog.fuzzy
 '
 
@@ -226,7 +226,7 @@ test_expect_success 'fail if the index has unresolved entries' '
 	test_commit modified2 file &&
 	git ls-files -u >unmerged &&
 	test_must_be_empty unmerged &&
-	test_must_fail git pull . second &&
+	test_must_fail git pull --no-rebase . second &&
 	git ls-files -u >unmerged &&
 	test_file_not_empty unmerged &&
 	cp file expected &&
@@ -409,37 +409,37 @@ test_expect_success 'pull --rebase --no-autostash & rebase.autostash unset' '
 
 test_expect_success 'pull succeeds with dirty working directory and merge.autostash set' '
 	test_config merge.autostash true &&
-	test_pull_autostash 2
+	test_pull_autostash 2 --no-rebase
 '
 
 test_expect_success 'pull --autostash & merge.autostash=true' '
 	test_config merge.autostash true &&
-	test_pull_autostash 2 --autostash
+	test_pull_autostash 2 --autostash --no-rebase
 '
 
 test_expect_success 'pull --autostash & merge.autostash=false' '
 	test_config merge.autostash false &&
-	test_pull_autostash 2 --autostash
+	test_pull_autostash 2 --autostash --no-rebase
 '
 
 test_expect_success 'pull --autostash & merge.autostash unset' '
 	test_unconfig merge.autostash &&
-	test_pull_autostash 2 --autostash
+	test_pull_autostash 2 --autostash --no-rebase
 '
 
 test_expect_success 'pull --no-autostash & merge.autostash=true' '
 	test_config merge.autostash true &&
-	test_pull_autostash_fail --no-autostash
+	test_pull_autostash_fail --no-autostash --no-rebase
 '
 
 test_expect_success 'pull --no-autostash & merge.autostash=false' '
 	test_config merge.autostash false &&
-	test_pull_autostash_fail --no-autostash
+	test_pull_autostash_fail --no-autostash --no-rebase
 '
 
 test_expect_success 'pull --no-autostash & merge.autostash unset' '
 	test_unconfig merge.autostash &&
-	test_pull_autostash_fail --no-autostash
+	test_pull_autostash_fail --no-autostash --no-rebase
 '
 
 test_expect_success 'pull.rebase' '

t/t5521-pull-options.sh

@@ -113,7 +113,7 @@ test_expect_success 'git pull --force' '
 	git pull two &&
 	test_commit A &&
 	git branch -f origin &&
-	git pull --all --force
+	git pull --no-rebase --all --force
 	)
 '
 
@@ -179,7 +179,7 @@ test_expect_success 'git pull --allow-unrelated-histories' '
 	(
 		cd dst &&
 		test_must_fail git pull ../src side &&
-		git pull --allow-unrelated-histories ../src side
+		git pull --no-rebase --allow-unrelated-histories ../src side
 	)
 '
 

t/t5524-pull-msg.sh

@@ -28,7 +28,7 @@ test_expect_success setup '
 test_expect_success pull '
 (
 	cd cloned &&
-	git pull --log &&
+	git pull --no-rebase --log &&
 	git log -2 &&
 	git cat-file commit HEAD >result &&
 	grep Dollar result
@@ -41,7 +41,7 @@ test_expect_success '--log=1 limits shortlog length' '
 	git reset --hard HEAD^ &&
 	test "$(cat afile)" = original &&
 	test "$(cat bfile)" = added &&
-	git pull --log=1 &&
+	git pull --no-rebase --log=1 &&
 	git log -3 &&
 	git cat-file commit HEAD >result &&
 	grep Dollar result &&

t/t5553-set-upstream.sh

@@ -108,27 +108,27 @@ test_expect_success 'setup commit on main and other pull' '
 
 test_expect_success 'pull --set-upstream upstream main sets branch main but not other' '
 	clear_config main other &&
-	git pull --set-upstream upstream main &&
+	git pull --no-rebase --set-upstream upstream main &&
 	check_config main upstream refs/heads/main &&
 	check_config_missing other
 '
 
 test_expect_success 'pull --set-upstream main:other2 does not set the branch other2' '
 	clear_config other2 &&
-	git pull --set-upstream upstream main:other2 &&
+	git pull --no-rebase --set-upstream upstream main:other2 &&
 	check_config_missing other2
 '
 
 test_expect_success 'pull --set-upstream upstream other sets branch main' '
 	clear_config main other &&
-	git pull --set-upstream upstream other &&
+	git pull --no-rebase --set-upstream upstream other &&
 	check_config main upstream refs/heads/other &&
 	check_config_missing other
 '
 
 test_expect_success 'pull --set-upstream upstream tag does not set the tag' '
 	clear_config three &&
-	git pull --tags --set-upstream upstream three &&
+	git pull --no-rebase --tags --set-upstream upstream three &&
 	check_config_missing three
 '
 
@@ -144,16 +144,16 @@ test_expect_success 'pull --set-upstream http://nosuchdomain.example.com fails w
 
 test_expect_success 'pull --set-upstream upstream HEAD sets branch HEAD' '
 	clear_config main other &&
-	git pull --set-upstream upstream HEAD &&
+	git pull --no-rebase --set-upstream upstream HEAD &&
 	check_config main upstream HEAD &&
 	git checkout other &&
-	git pull --set-upstream upstream HEAD &&
+	git pull --no-rebase --set-upstream upstream HEAD &&
 	check_config other upstream HEAD
 '
 
 test_expect_success 'pull --set-upstream upstream with more than one branch does nothing' '
 	clear_config main three &&
-	git pull --set-upstream upstream main three &&
+	git pull --no-rebase --set-upstream upstream main three &&
 	check_config_missing main &&
 	check_config_missing three
 '

t/t5604-clone-reference.sh

@@ -87,7 +87,7 @@ test_expect_success 'updating origin' '
 '
 
 test_expect_success 'pulling changes from origin' '
-	git -C C pull origin
+	git -C C pull --no-rebase origin
 '
 
 # the 2 local objects are commit and tree from the merge
@@ -96,7 +96,7 @@ test_expect_success 'that alternate to origin gets used' '
 '
 
 test_expect_success 'pulling changes from origin' '
-	git -C D pull origin
+	git -C D pull --no-rebase origin
 '
 
 # the 5 local objects are expected; file3 blob, commit in A to add it

t/t6402-merge-rename.sh

@@ -103,7 +103,7 @@ test_expect_success 'setup' '
 test_expect_success 'pull renaming branch into unrenaming one' \
 '
 	git show-branch &&
-	test_expect_code 1 git pull . white &&
+	test_expect_code 1 git pull --no-rebase . white &&
 	git ls-files -s &&
 	test_stdout_line_count = 3 git ls-files -u B &&
 	test_stdout_line_count = 1 git ls-files -s N &&
@@ -119,7 +119,7 @@ test_expect_success 'pull renaming branch into another renaming one' \
 	rm -f B &&
 	git reset --hard &&
 	git checkout red &&
-	test_expect_code 1 git pull . white &&
+	test_expect_code 1 git pull --no-rebase . white &&
 	test_stdout_line_count = 3 git ls-files -u B &&
 	test_stdout_line_count = 1 git ls-files -s N &&
 	sed -ne "/^g/{
@@ -133,7 +133,7 @@ test_expect_success 'pull unrenaming branch into renaming one' \
 '
 	git reset --hard &&
 	git show-branch &&
-	test_expect_code 1 git pull . main &&
+	test_expect_code 1 git pull --no-rebase . main &&
 	test_stdout_line_count = 3 git ls-files -u B &&
 	test_stdout_line_count = 1 git ls-files -s N &&
 	sed -ne "/^g/{
@@ -147,7 +147,7 @@ test_expect_success 'pull conflicting renames' \
 '
 	git reset --hard &&
 	git show-branch &&
-	test_expect_code 1 git pull . blue &&
+	test_expect_code 1 git pull --no-rebase . blue &&
 	test_stdout_line_count = 1 git ls-files -u A &&
 	test_stdout_line_count = 1 git ls-files -u B &&
 	test_stdout_line_count = 1 git ls-files -u C &&
@@ -163,7 +163,7 @@ test_expect_success 'interference with untracked working tree file' '
 	git reset --hard &&
 	git show-branch &&
 	echo >A this file should not matter &&
-	test_expect_code 1 git pull . white &&
+	test_expect_code 1 git pull --no-rebase . white &&
 	test_path_is_file A
 '
 
@@ -173,7 +173,7 @@ test_expect_success 'interference with untracked working tree file' '
 	git show-branch &&
 	rm -f A &&
 	echo >A this file should not matter &&
-	test_expect_code 1 git pull . red &&
+	test_expect_code 1 git pull --no-rebase . red &&
 	test_path_is_file A
 '
 
@@ -183,7 +183,7 @@ test_expect_success 'interference with untracked working tree file' '
 	git checkout -f main &&
 	git tag -f anchor &&
 	git show-branch &&
-	git pull . yellow &&
+	git pull --no-rebase . yellow &&
 	test_path_is_missing M &&
 	git reset --hard anchor
 '
@@ -210,7 +210,7 @@ test_expect_success 'updated working tree file should prevent the merge' '
 	echo >>M one line addition &&
 	cat M >M.saved &&
 	git update-index M &&
-	test_expect_code 128 git pull . yellow &&
+	test_expect_code 128 git pull --no-rebase . yellow &&
 	test_cmp M M.saved &&
 	rm -f M.saved
 '
@@ -222,7 +222,7 @@ test_expect_success 'interference with untracked working tree file' '
 	git tag -f anchor &&
 	git show-branch &&
 	echo >M this file should not matter &&
-	git pull . main &&
+	git pull --no-rebase . main &&
 	test_path_is_file M &&
 	! {
 		git ls-files -s |

t/t6409-merge-subtree.sh

@@ -100,7 +100,7 @@ test_expect_success 'merge update' '
 	git checkout -b topic_2 &&
 	git commit -m "update git-gui" &&
 	cd ../git &&
-	git pull -s subtree gui topic_2 &&
+	git pull --no-rebase -s subtree gui topic_2 &&
 	git ls-files -s >actual &&
 	(
 		echo "100644 $o3 0	git-gui/git-gui.sh" &&
@@ -129,7 +129,7 @@ test_expect_success 'initial ambiguous subtree' '
 test_expect_success 'merge using explicit' '
 	cd ../git &&
 	git reset --hard topic_2 &&
-	git pull -Xsubtree=git-gui gui topic_2 &&
+	git pull --no-rebase -Xsubtree=git-gui gui topic_2 &&
 	git ls-files -s >actual &&
 	(
 		echo "100644 $o3 0	git-gui/git-gui.sh" &&
@@ -142,7 +142,7 @@ test_expect_success 'merge using explicit' '
 test_expect_success 'merge2 using explicit' '
 	cd ../git &&
 	git reset --hard topic_2 &&
-	git pull -Xsubtree=git-gui2 gui topic_2 &&
+	git pull --no-rebase -Xsubtree=git-gui2 gui topic_2 &&
 	git ls-files -s >actual &&
 	(
 		echo "100644 $o1 0	git-gui/git-gui.sh" &&

t/t6417-merge-ours-theirs.sh

@@ -69,11 +69,11 @@ test_expect_success 'binary file with -Xours/-Xtheirs' '
 '
 
 test_expect_success 'pull passes -X to underlying merge' '
-	git reset --hard main && git pull -s recursive -Xours . side &&
-	git reset --hard main && git pull -s recursive -X ours . side &&
-	git reset --hard main && git pull -s recursive -Xtheirs . side &&
-	git reset --hard main && git pull -s recursive -X theirs . side &&
-	git reset --hard main && test_must_fail git pull -s recursive -X bork . side
+	git reset --hard main && git pull --no-rebase -s recursive -Xours . side &&
+	git reset --hard main && git pull --no-rebase -s recursive -X ours . side &&
+	git reset --hard main && git pull --no-rebase -s recursive -Xtheirs . side &&
+	git reset --hard main && git pull --no-rebase -s recursive -X theirs . side &&
+	git reset --hard main && test_must_fail git pull --no-rebase -s recursive -X bork . side
 '
 
 test_expect_success SYMLINKS 'symlink with -Xours/-Xtheirs' '

t/t7601-merge-pull-config.sh

@@ -27,120 +27,324 @@ test_expect_success 'setup' '
 	git tag c3
 '
 
-test_expect_success 'pull.rebase not set' '
+test_expect_success 'pull.rebase not set, ff possible' '
 	git reset --hard c0 &&
 	git pull . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and pull.ff=true' '
 	git reset --hard c0 &&
 	test_config pull.ff true &&
 	git pull . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and pull.ff=false' '
 	git reset --hard c0 &&
 	test_config pull.ff false &&
 	git pull . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and pull.ff=only' '
 	git reset --hard c0 &&
 	test_config pull.ff only &&
 	git pull . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --rebase given' '
 	git reset --hard c0 &&
 	git pull --rebase . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --no-rebase given' '
 	git reset --hard c0 &&
 	git pull --no-rebase . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --ff given' '
 	git reset --hard c0 &&
 	git pull --ff . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --no-ff given' '
 	git reset --hard c0 &&
 	git pull --no-ff . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --ff-only given' '
 	git reset --hard c0 &&
 	git pull --ff-only . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set (not-fast-forward)' '
 	git reset --hard c2 &&
-	git -c color.advice=always pull . c1 2>err &&
+	test_must_fail git -c color.advice=always pull . c1 2>err &&
 	test_decode_color <err >decoded &&
 	test_i18ngrep "<YELLOW>hint: " decoded &&
-	test_i18ngrep "Pulling without specifying how to reconcile" decoded
+	test_i18ngrep "You have divergent branches" decoded
 '
 
 test_expect_success 'pull.rebase not set and pull.ff=true (not-fast-forward)' '
 	git reset --hard c2 &&
 	test_config pull.ff true &&
 	git pull . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and pull.ff=false (not-fast-forward)' '
 	git reset --hard c2 &&
 	test_config pull.ff false &&
 	git pull . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and pull.ff=only (not-fast-forward)' '
 	git reset --hard c2 &&
 	test_config pull.ff only &&
 	test_must_fail git pull . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --rebase given (not-fast-forward)' '
 	git reset --hard c2 &&
 	git pull --rebase . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --no-rebase given (not-fast-forward)' '
 	git reset --hard c2 &&
 	git pull --no-rebase . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --ff given (not-fast-forward)' '
 	git reset --hard c2 &&
 	git pull --ff . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --no-ff given (not-fast-forward)' '
 	git reset --hard c2 &&
 	git pull --no-ff . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
 '
 
 test_expect_success 'pull.rebase not set and --ff-only given (not-fast-forward)' '
 	git reset --hard c2 &&
 	test_must_fail git pull --ff-only . c1 2>err &&
-	test_i18ngrep ! "Pulling without specifying how to reconcile" err
+	test_i18ngrep ! "You have divergent branches" err
+'
+
+test_does_rebase () {
+	git reset --hard c2 &&
+	git "$@" . c1 &&
+	# Check that we actually did a rebase
+	git rev-list --count HEAD >actual &&
+	git rev-list --merges --count HEAD >>actual &&
+	test_write_lines 3 0 >expect &&
+	test_cmp expect actual &&
+	rm actual expect
+}
+
+# Prefers merge over fast-forward
+test_does_merge_when_ff_possible () {
+	git reset --hard c0 &&
+	git "$@" . c1 &&
+	# Check that we actually did a merge
+	git rev-list --count HEAD >actual &&
+	git rev-list --merges --count HEAD >>actual &&
+	test_write_lines 3 1 >expect &&
+	test_cmp expect actual &&
+	rm actual expect
+}
+
+# Prefers fast-forward over merge or rebase
+test_does_fast_forward () {
+	git reset --hard c0 &&
+	git "$@" . c1 &&
+
+	# Check that we did not get any merges
+	git rev-list --count HEAD >actual &&
+	git rev-list --merges --count HEAD >>actual &&
+	test_write_lines 2 0 >expect &&
+	test_cmp expect actual &&
+
+	# Check that we ended up at c1
+	git rev-parse HEAD >actual &&
+	git rev-parse c1^{commit} >expect &&
+	test_cmp actual expect &&
+
+	# Remove temporary files
+	rm actual expect
+}
+
+# Doesn't fail when fast-forward not possible; does a merge
+test_falls_back_to_full_merge () {
+	git reset --hard c2 &&
+	git "$@" . c1 &&
+	# Check that we actually did a merge
+	git rev-list --count HEAD >actual &&
+	git rev-list --merges --count HEAD >>actual &&
+	test_write_lines 4 1 >expect &&
+	test_cmp expect actual &&
+	rm actual expect
+}
+
+# Attempts fast forward, which is impossible, and bails
+test_attempts_fast_forward () {
+	git reset --hard c2 &&
+	test_must_fail git "$@" . c1 2>err &&
+	test_i18ngrep "Not possible to fast-forward, aborting" err
+}
+
+#
+# Group 1: Interaction of --ff-only with --[no-]rebase
+# (And related interaction of pull.ff=only with pull.rebase)
+#
+test_expect_success '--ff-only overrides --rebase' '
+	test_attempts_fast_forward pull --rebase --ff-only
+'
+
+test_expect_success '--ff-only overrides --rebase even if first' '
+	test_attempts_fast_forward pull --ff-only --rebase
+'
+
+test_expect_success '--ff-only overrides --no-rebase' '
+	test_attempts_fast_forward pull --ff-only --no-rebase
+'
+
+test_expect_success 'pull.ff=only overrides pull.rebase=true' '
+	test_attempts_fast_forward -c pull.ff=only -c pull.rebase=true pull
+'
+
+test_expect_success 'pull.ff=only overrides pull.rebase=false' '
+	test_attempts_fast_forward -c pull.ff=only -c pull.rebase=false pull
+'
+
+# Group 2: --rebase=[!false] overrides --no-ff and --ff
+# (And related interaction of pull.rebase=!false and pull.ff=!only)
+test_expect_success '--rebase overrides --no-ff' '
+	test_does_rebase pull --rebase --no-ff
+'
+
+test_expect_success '--rebase overrides --ff' '
+	test_does_rebase pull --rebase --ff
+'
+
+test_expect_success '--rebase fast-forwards when possible' '
+	test_does_fast_forward pull --rebase --ff
+'
+
+test_expect_success 'pull.rebase=true overrides pull.ff=false' '
+	test_does_rebase -c pull.rebase=true -c pull.ff=false pull
+'
+
+test_expect_success 'pull.rebase=true overrides pull.ff=true' '
+	test_does_rebase -c pull.rebase=true -c pull.ff=true pull
+'
+
+# Group 3: command line flags take precedence over config
+test_expect_success '--ff-only takes precedence over pull.rebase=true' '
+	test_attempts_fast_forward -c pull.rebase=true pull --ff-only
+'
+
+test_expect_success '--ff-only takes precedence over pull.rebase=false' '
+	test_attempts_fast_forward -c pull.rebase=false pull --ff-only
+'
+
+test_expect_success '--no-rebase takes precedence over pull.ff=only' '
+	test_falls_back_to_full_merge -c pull.ff=only pull --no-rebase
+'
+
+test_expect_success '--rebase takes precedence over pull.ff=only' '
+	test_does_rebase -c pull.ff=only pull --rebase
+'
+
+test_expect_success '--rebase overrides pull.ff=true' '
+	test_does_rebase -c pull.ff=true pull --rebase
+'
+
+test_expect_success '--rebase overrides pull.ff=false' '
+	test_does_rebase -c pull.ff=false pull --rebase
+'
+
+test_expect_success '--rebase overrides pull.ff unset' '
+	test_does_rebase pull --rebase
+'
+
+# Group 4: --no-rebase heeds pull.ff=!only or explict --ff or --no-ff
+
+test_expect_success '--no-rebase works with --no-ff' '
+	test_does_merge_when_ff_possible pull --no-rebase --no-ff
+'
+
+test_expect_success '--no-rebase works with --ff' '
+	test_does_fast_forward pull --no-rebase --ff
+'
+
+test_expect_success '--no-rebase does ff if pull.ff unset' '
+	test_does_fast_forward pull --no-rebase
+'
+
+test_expect_success '--no-rebase heeds pull.ff=true' '
+	test_does_fast_forward -c pull.ff=true pull --no-rebase
+'
+
+test_expect_success '--no-rebase heeds pull.ff=false' '
+	test_does_merge_when_ff_possible -c pull.ff=false pull --no-rebase
+'
+
+# Group 5: pull.rebase=!false in combination with --no-ff or --ff
+test_expect_success 'pull.rebase=true and --no-ff' '
+	test_does_rebase -c pull.rebase=true pull --no-ff
+'
+
+test_expect_success 'pull.rebase=true and --ff' '
+	test_does_rebase -c pull.rebase=true pull --ff
+'
+
+test_expect_success 'pull.rebase=false and --no-ff' '
+	test_does_merge_when_ff_possible -c pull.rebase=false pull --no-ff
+'
+
+test_expect_success 'pull.rebase=false and --ff, ff possible' '
+	test_does_fast_forward -c pull.rebase=false pull --ff
+'
+
+test_expect_success 'pull.rebase=false and --ff, ff not possible' '
+	test_falls_back_to_full_merge -c pull.rebase=false pull --ff
+'
+
+# End of groupings for conflicting merge vs. rebase flags/options
+
+test_expect_success 'Multiple heads warns about inability to fast forward' '
+	git reset --hard c1 &&
+	test_must_fail git pull . c2 c3 2>err &&
+	test_i18ngrep "You have divergent branches" err
+'
+
+test_expect_success 'Multiple can never be fast forwarded' '
+	git reset --hard c0 &&
+	test_must_fail git -c pull.ff=only pull . c1 c2 c3 2>err &&
+	test_i18ngrep ! "You have divergent branches" err &&
+	# In addition to calling out "cannot fast-forward", we very much
+	# want the "multiple branches" piece to be called out to users.
+	test_i18ngrep "Cannot fast-forward to multiple branches" err
+'
+
+test_expect_success 'Cannot rebase with multiple heads' '
+	git reset --hard c0 &&
+	test_must_fail git -c pull.rebase=true pull . c1 c2 c3 2>err &&
+	test_i18ngrep ! "You have divergent branches" err &&
+	test_i18ngrep "Cannot rebase onto multiple branches." err
 '
 
 test_expect_success 'merge c1 with c2' '

t/t7603-merge-reduce-heads.sh

@@ -68,7 +68,7 @@ test_expect_success 'merge c1 with c2, c3, c4, c5' '
 
 test_expect_success 'pull c2, c3, c4, c5 into c1' '
 	git reset --hard c1 &&
-	git pull . c2 c3 c4 c5 &&
+	git pull --no-rebase . c2 c3 c4 c5 &&
 	test "$(git rev-parse c1)" != "$(git rev-parse HEAD)" &&
 	test "$(git rev-parse c1)" = "$(git rev-parse HEAD^1)" &&
 	test "$(git rev-parse c2)" = "$(git rev-parse HEAD^2)" &&