rebase: validate -C<n> and --whitespace=<mode> parameters early

It is a good idea to error out early upon seeing, say, `-Cbad`, rather
than starting the rebase only to have the `--am` backend complain later.

Let's do this.

The only options accepting parameters which we pass through to `git am`
(which may, or may not, forward them to `git apply`) are `-C` and
`--whitespace`. The other options we pass through do not accept
parameters, so we do not have to validate them here.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/rebase.c

@@ -1064,12 +1064,22 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	}
 
 	for (i = 0; i < options.git_am_opts.argc; i++) {
-		const char *option = options.git_am_opts.argv[i];
+		const char *option = options.git_am_opts.argv[i], *p;
 		if (!strcmp(option, "--committer-date-is-author-date") ||
 		    !strcmp(option, "--ignore-date") ||
 		    !strcmp(option, "--whitespace=fix") ||
 		    !strcmp(option, "--whitespace=strip"))
 			options.flags |= REBASE_FORCE;
+		else if (skip_prefix(option, "-C", &p)) {
+			while (*p)
+				if (!isdigit(*(p++)))
+					die(_("switch `C' expects a "
+					      "numerical value"));
+		} else if (skip_prefix(option, "--whitespace=", &p)) {
+			if (*p && strcmp(p, "warn") && strcmp(p, "nowarn") &&
+			    strcmp(p, "error") && strcmp(p, "error-all"))
+				die("Invalid whitespace option: '%s'", p);
+		}
 	}
 
 	if (!(options.flags & REBASE_NO_QUIET))

t/t3406-rebase-message.sh

@@ -84,4 +84,11 @@ test_expect_success 'rebase --onto outputs the invalid ref' '
 	test_i18ngrep "invalid-ref" err
 '
 
+test_expect_success 'error out early upon -C<n> or --whitespace=<bad>' '
+	test_must_fail git rebase -Cnot-a-number HEAD 2>err &&
+	test_i18ngrep "numerical value" err &&
+	test_must_fail git rebase --whitespace=bad HEAD 2>err &&
+	test_i18ngrep "Invalid whitespace option" err
+'
+
 test_done