Merge branch 'jk/diff-follow-must-take-one-pathspec' into maint

"git format-patch" did not enforce the rule that the "--follow"
option from the log/diff family of commands must be used with
exactly one pathspec.

* jk/diff-follow-must-take-one-pathspec:
  move "--follow needs one pathspec" rule to diff_setup_done

Author: gitster

builtin/log.c

@@ -158,13 +158,9 @@ static void cmd_log_init_finish(int argc, const char **argv, const char *prefix,
 	if (rev->show_notes)
 		init_display_notes(&rev->notes_opt);
 
-	if (rev->diffopt.pickaxe || rev->diffopt.filter)
+	if (rev->diffopt.pickaxe || rev->diffopt.filter ||
+	    DIFF_OPT_TST(&rev->diffopt, FOLLOW_RENAMES))
 		rev->always_show_header = 0;
-	if (DIFF_OPT_TST(&rev->diffopt, FOLLOW_RENAMES)) {
-		rev->always_show_header = 0;
-		if (rev->diffopt.pathspec.nr != 1)
-			usage("git logs can only follow renames on one pathname at a time");
-	}
 
 	if (source)
 		rev->show_source = 1;

diff.c

@@ -3325,6 +3325,9 @@ void diff_setup_done(struct diff_options *options)
 	}
 
 	options->diff_path_counter = 0;
+
+	if (DIFF_OPT_TST(options, FOLLOW_RENAMES) && options->pathspec.nr != 1)
+		die(_("--follow requires exactly one pathspec"));
 }
 
 static int opt_arg(const char *arg, int arg_short, const char *arg_long, int *val)