[PATCH 3/9] pull: abort if --ff-only is given and fast-forwarding is impossible

["Alex Henrie via GitGitGadget" <gitgitgadget@xxxxxxxxx>]

From: Alex Henrie <alexhenrie24@xxxxxxxxx>

The warning about pulling without specifying how to reconcile divergent
branches says that after setting pull.rebase to true, --ff-only can
still be passed on the command line to require a fast-forward. Make that
actually work.

Signed-off-by: Alex Henrie <alexhenrie24@xxxxxxxxx>
[en: updated tests; note 3 fixes and 1 new failure]
Signed-off-by: Elijah Newren <newren@xxxxxxxxx>
---
 advice.c                     |  5 +++++
 advice.h                     |  1 +
 builtin/merge.c              |  2 +-
 builtin/pull.c               | 11 ++++++++---
 t/t7601-merge-pull-config.sh | 10 +++++-----
 5 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/advice.c b/advice.c
index 0b9c89c48ab..337e8f342bc 100644
--- a/advice.c
+++ b/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;
diff --git a/advice.h b/advice.h
index bd26c385d00..16240438387 100644
--- a/advice.h
+++ b/advice.h
@@ -95,6 +95,7 @@ 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);
 
diff --git a/builtin/merge.c b/builtin/merge.c
index a8a843b1f54..aa920ac524f 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -1620,7 +1620,7 @@ 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,
diff --git a/builtin/pull.c b/builtin/pull.c
index 3e13f810843..d9796604825 100644
--- a/builtin/pull.c
+++ b/builtin/pull.c
@@ -1046,9 +1046,14 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 
 	can_ff = get_can_ff(&orig_head, &merge_heads.oid[0]);
 
-	if (rebase_unspecified && !opt_ff && !can_ff) {
-		if (opt_verbosity >= 0)
-			show_advice_pull_non_ff();
+	if (!can_ff) {
+		if (opt_ff) {
+			if (!strcmp(opt_ff, "--ff-only"))
+				die_ff_impossible();
+		} else {
+			if (rebase_unspecified && opt_verbosity >= 0)
+				show_advice_pull_non_ff();
+		}
 	}
 
 	if (opt_rebase) {
diff --git a/t/t7601-merge-pull-config.sh b/t/t7601-merge-pull-config.sh
index 40d8fb95113..23a1fbc17b3 100755
--- a/t/t7601-merge-pull-config.sh
+++ b/t/t7601-merge-pull-config.sh
@@ -197,11 +197,11 @@ test_attempts_fast_forward() {
 # Rule 1: --ff-only takes precedence over --[no-]rebase
 # (Corollary: pull.ff=only overrides pull.rebase)
 #
-test_expect_failure '--ff-only takes precedence over --rebase' '
+test_expect_success '--ff-only takes precedence over --rebase' '
 	test_attempts_fast_forward pull --rebase --ff-only
 '
 
-test_expect_failure '--ff-only takes precedence over --rebase even if first' '
+test_expect_success '--ff-only takes precedence over --rebase even if first' '
 	test_attempts_fast_forward pull --ff-only --rebase
 '
 
@@ -209,7 +209,7 @@ test_expect_success '--ff-only takes precedence over --no-rebase' '
 	test_attempts_fast_forward pull --ff-only --no-rebase
 '
 
-test_expect_failure 'pull.ff=only overrides pull.rebase=true' '
+test_expect_success 'pull.ff=only overrides pull.rebase=true' '
 	test_attempts_fast_forward -c pull.ff=only -c pull.rebase=true pull
 '
 
@@ -236,7 +236,7 @@ test_expect_success 'pull.rebase=true takes precedence over pull.ff=true' '
 '
 
 # Rule 3: command line flags take precedence over config
-test_expect_failure '--ff-only takes precedence over pull.rebase=true' '
+test_expect_success '--ff-only takes precedence over pull.rebase=true' '
 	test_attempts_fast_forward -c pull.rebase=true pull --ff-only
 '
 
@@ -248,7 +248,7 @@ test_expect_failure '--no-rebase overrides pull.ff=only' '
 	test_does_need_full_merge -c pull.ff=only pull --no-rebase
 '
 
-test_expect_success '--rebase takes precedence over pull.ff=only' '
+test_expect_failure '--rebase takes precedence over pull.ff=only' '
 	test_does_rebase -c pull.ff=only pull --rebase
 '
 
-- 
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