[PATCH 2/7] merge: add diverging advice for novices
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git@vger.kernel.org
Cc
Alex Henrie
Ævar Arnfjörð Bjarmason
Randall S . Becker
Nguyễn Thái Ngọc Duy
Denton Liu
Elijah Newren
Junio C Hamano
Felipe Contreras
From
Felipe Contreras
See Also
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Date
2021-07-22 00:08:49 UTC
Diverging branches is one of the most confusing aspects of distributed
version control systems for novices, so a little help explaining what to
do on those situations will come in handy.

Right now this advice will be displayed only when the user does
`git merge --ff-only`, `git pull --ff-only`, or has configured
`pull.ff=only` for `git pull`, but in the future it's expected that
--ff-only will be the default for `git pull`, and a proposed `git
fast-forward` command will imply --ff-only, in addition to `git update`.

So it makes sense to add the advice in preparation for those future
changes, although even currently it helps.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
---
 advice.c        | 11 +++++++++++
 advice.h        |  1 +
 builtin/merge.c |  4 +++-
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/advice.c b/advice.c
index 0b9c89c48a..8f068c8be9 100644
--- a/advice.c
+++ b/advice.c
@@ -326,3 +326,14 @@ void detach_advice(const char *new_name)
 
 	fprintf(stderr, fmt, new_name);
 }
+
+void diverging_advice(void)
+{
+	advise(_("Diverging branches can't be fast-forwarded, you need to either:\n"
+		"\n"
+		"\tgit merge\n"
+		"\n"
+		"or:\n"
+		"\n"
+		"\tgit rebase\n"));
+}
diff --git a/advice.h b/advice.h
index bd26c385d0..6ce967c962 100644
--- a/advice.h
+++ b/advice.h
@@ -97,5 +97,6 @@ void NORETURN die_resolve_conflict(const char *me);
 void NORETURN die_conclude_merge(void);
 void advise_on_updating_sparse_paths(struct string_list *pathspec_list);
 void detach_advice(const char *new_name);
+void diverging_advice(void);
 
 #endif /* ADVICE_H */
diff --git a/builtin/merge.c b/builtin/merge.c
index 05e631229d..56a526f42c 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -1619,8 +1619,10 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		}
 	}
 
-	if (fast_forward == FF_ONLY)
+	if (fast_forward == FF_ONLY) {
+		diverging_advice();
 		die(_("unable to fast-forward"));
+	}
 
 	if (autostash)
 		create_autostash(the_repository,
-- 
2.32.0.40.gb9b36f9b52