fast-export: check for unsupported signing modes earlier

The '--signed-{commits,tags}' options for git-fast-export(1) support
only a subset of the modes accepted by git-fast-import(1). Unsupported
modes such as 'strip-if-invalid' and 'sign-if-invalid' are accepted
during option parsing, but cause the command to die later when a signed
object is encountered.

Instead, reject unsupported signing modes immediately after parsing the
option. This treats them the same as other unknown modes and avoids
deferring the error until object processing. This also removes
duplicated checks in commit/tag handling code.

Signed-off-by: Justin Tobler <jltobler@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: jltobler

builtin/fast-export.c

@@ -64,7 +64,8 @@ static int parse_opt_sign_mode(const struct option *opt,
 	if (unset)
 		return 0;
 
-	if (parse_sign_mode(arg, val, NULL))
+	if (parse_sign_mode(arg, val, NULL) || (*val == SIGN_STRIP_IF_INVALID) ||
+	    (*val == SIGN_SIGN_IF_INVALID))
 		return error(_("unknown %s mode: %s"), opt->long_name, arg);
 
 	return 0;
@@ -822,12 +823,6 @@ static void handle_commit(struct commit *commit, struct rev_info *rev,
 			die(_("encountered signed commit %s; use "
 			      "--signed-commits=<mode> to handle it"),
 			    oid_to_hex(&commit->object.oid));
-		case SIGN_STRIP_IF_INVALID:
-			die(_("'strip-if-invalid' is not a valid mode for "
-			      "git fast-export with --signed-commits=<mode>"));
-		case SIGN_SIGN_IF_INVALID:
-			die(_("'sign-if-invalid' is not a valid mode for "
-			      "git fast-export with --signed-commits=<mode>"));
 		default:
 			BUG("invalid signed_commit_mode value %d", signed_commit_mode);
 		}
@@ -970,12 +965,6 @@ static void handle_tag(const char *name, struct tag *tag)
 				die(_("encountered signed tag %s; use "
 				      "--signed-tags=<mode> to handle it"),
 				    oid_to_hex(&tag->object.oid));
-			case SIGN_STRIP_IF_INVALID:
-				die(_("'strip-if-invalid' is not a valid mode for "
-				      "git fast-export with --signed-tags=<mode>"));
-			case SIGN_SIGN_IF_INVALID:
-				die(_("'sign-if-invalid' is not a valid mode for "
-				      "git fast-export with --signed-tags=<mode>"));
 			default:
 				BUG("invalid signed_commit_mode value %d", signed_commit_mode);
 			}