[PATCH v2 10/14] pull: add proper error with --ff-only

From: Felipe Contreras <felipe.contreras@gmail.com>
To: git@vger.kernel.org
Cc: "Vít Ondruch" <vondruch@redhat.com>,
	"Alex Henrie" <alexhenrie24@gmail.com>,
	"Junio C Hamano" <gitster@pobox.com>, "Jeff King" <peff@peff.net>,
	"Philip Oakley" <philipoakley@iee.email>,
	"Theodore Y . Ts'o" <tytso@mit.edu>,
	"Jacob Keller" <jacob.keller@gmail.com>,
	"Elijah Newren" <newren@gmail.com>,
	"John Keeping" <john@keeping.me.uk>,
	"Richard Hansen" <rhansen@rhansen.org>,
	"Brian M. Carlson" <sandals@crustytoothpaste.net>,
	"W. Trevor King" <wking@tremily.us>,
	"Felipe Contreras" <felipe.contreras@gmail.com>
Subject: [PATCH v2 10/14] pull: add proper error with --ff-only
Date: Fri,  4 Dec 2020 00:16:19 -0600	[thread overview]
Message-ID: <20201204061623.1170745-11-felipe.contreras@gmail.com> (raw)
In-Reply-To: <20201204061623.1170745-1-felipe.contreras@gmail.com>

The current error is not user-friendly:

  fatal: not possible to fast-forward, aborting.

We want something that actually explains what is going on:

  The pull was not fast-forward, please either merge or rebase.
  If unsure, run "git pull --merge".

The user can get rid of the warning by doing either --merge or
--rebase.

Except: doing "git pull --merge" is not actually enough; we would return
to the previous behavior: "fatal: not possible to fast-forward, aborting."

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
---
 builtin/pull.c  | 34 ++++++++++++++++-----------
 t/t5520-pull.sh | 62 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 82 insertions(+), 14 deletions(-)

diff --git a/builtin/pull.c b/builtin/pull.c
index 6ea95c9fc9..f54ff36b57 100644
--- a/builtin/pull.c
+++ b/builtin/pull.c
@@ -1015,20 +1015,26 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 
 	can_ff = get_can_ff(&orig_head, &merge_heads.oid[0]);
 
-	if (default_mode && !can_ff && opt_verbosity >= 0 && !opt_ff) {
-		advise(_("Pulling without specifying how to reconcile divergent branches is\n"
-			"discouraged; you need to specify if you want a merge, or a rebase.\n"
-			"You can squelch this message by running one of the following commands:\n"
-			"\n"
-			"  git config pull.rebase false  # merge (the default strategy)\n"
-			"  git config pull.rebase true   # rebase\n"
-			"  git config pull.ff only       # fast-forward only\n"
-			"\n"
-			"You can replace \"git config\" with \"git config --global\" to set a default\n"
-			"preference for all repositories.\n"
-			"If unsure, run \"git pull --merge\".\n"
-			"Read \"git pull --help\" for more information."
-			));
+	if (!can_ff && default_mode) {
+		if (opt_ff && !strcmp(opt_ff, "--ff-only")) {
+			die(_("The pull was not fast-forward, please either merge or rebase.\n"
+				"If unsure, run \"git pull --merge\"."));
+		}
+		if (opt_verbosity >= 0 && !opt_ff) {
+			advise(_("Pulling without specifying how to reconcile divergent branches is\n"
+				"discouraged; you need to specify if you want a merge, or a rebase.\n"
+				"You can squelch this message by running one of the following commands:\n"
+				"\n"
+				"  git config pull.rebase false  # merge (the default strategy)\n"
+				"  git config pull.rebase true   # rebase\n"
+				"  git config pull.ff only       # fast-forward only\n"
+				"\n"
+				"You can replace \"git config\" with \"git config --global\" to set a default\n"
+				"preference for all repositories.\n"
+				"If unsure, run \"git pull --merge\".\n"
+				"Read \"git pull --help\" for more information."
+				));
+		}
 	}
 
 	if (opt_rebase) {
diff --git a/t/t5520-pull.sh b/t/t5520-pull.sh
index 9fae07cdfa..fdd1f79b06 100755
--- a/t/t5520-pull.sh
+++ b/t/t5520-pull.sh
@@ -819,4 +819,66 @@ test_expect_success 'git pull --rebase against local branch' '
 	test_cmp expect file2
 '
 
+test_expect_success 'git pull fast-forward (ff-only)' '
+	test_when_finished "git checkout master && git branch -D other test" &&
+	test_config pull.ff only &&
+	git checkout -b other master &&
+	>new &&
+	git add new &&
+	git commit -m new &&
+	git checkout -b test -t other &&
+	git reset --hard master &&
+	git pull
+'
+
+test_expect_success 'git pull non-fast-forward (ff-only)' '
+	test_when_finished "git checkout master && git branch -D other test" &&
+	test_config pull.ff only &&
+	git checkout -b other master^ &&
+	>new &&
+	git add new &&
+	git commit -m new &&
+	git checkout -b test -t other &&
+	git reset --hard master &&
+	test_must_fail git pull
+'
+
+test_expect_failure 'git pull non-fast-forward with merge (ff-only)' '
+	test_when_finished "git checkout master && git branch -D other test" &&
+	test_config pull.ff only &&
+	git checkout -b other master^ &&
+	>new &&
+	git add new &&
+	git commit -m new &&
+	git checkout -b test -t other &&
+	git reset --hard master &&
+	git pull --no-rebase
+'
+
+test_expect_success 'git pull non-fast-forward with rebase (ff-only)' '
+	test_when_finished "git checkout master && git branch -D other test" &&
+	test_config pull.ff only &&
+	git checkout -b other master^ &&
+	>new &&
+	git add new &&
+	git commit -m new &&
+	git checkout -b test -t other &&
+	git reset --hard master &&
+	git pull --rebase
+'
+
+test_expect_success 'git pull non-fast-forward error message' '
+	test_when_finished "git checkout master && git branch -D other test" &&
+	test_config pull.ff only &&
+	git checkout -b other master^ &&
+	>new &&
+	git add new &&
+	git commit -m new &&
+	git checkout -b test -t other &&
+	git reset --hard master &&
+	test_must_fail git pull 2> error &&
+	cat error &&
+	grep -q "The pull was not fast-forward" error
+'
+
 test_done
-- 
2.29.2

