Merge branch 'tr/merge-edit-guidance' into maint

* tr/merge-edit-guidance:
  merge: add instructions to the commit message when editing

builtin/merge.c

@@ -885,11 +885,21 @@ static void abort_commit(const char *err_msg)
 	exit(1);
 }
 
+static const char merge_editor_comment[] =
+N_("Please enter a commit message to explain why this merge is necessary,\n"
+   "especially if it merges an updated upstream into a topic branch.\n"
+   "\n"
+   "Lines starting with '#' will be ignored, and an empty message aborts\n"
+   "the commit.\n");
+
 static void prepare_to_commit(void)
 {
 	struct strbuf msg = STRBUF_INIT;
+	const char *comment = _(merge_editor_comment);
 	strbuf_addbuf(&msg, &merge_msg);
 	strbuf_addch(&msg, '\n');
+	if (0 < option_edit)
+		strbuf_add_lines(&msg, "# ", comment, strlen(comment));
 	write_merge_msg(&msg);
 	run_hook(get_index_file(), "prepare-commit-msg",
 		 git_path("MERGE_MSG"), "merge", NULL, NULL);