+/*
+ * Check whether the string `term` belongs to the set of strings
+ * included in the variable arguments.
+ */
+LAST_ARG_MUST_BE_NULL
+static int one_of(const char *term, ...)
+{
+ int res = 0;
+ va_list matches;
+ const char *match;
+
+ va_start(matches, term);
+ while (!res && (match = va_arg(matches, const char *)))
+ res = !strcmp(term, match);
+ va_end(matches);
+
+ return res;
+}
+
+static int check_term_format(const char *term, const char *orig_term)
+{
+ int res;
+ char *new_term = xstrfmt("refs/bisect/%s", term);
+
+ res = check_refname_format(new_term, 0);
+ free(new_term);
+
+ if (res)
+ return error(_("'%s' is not a valid term"), term);
+
+ if (one_of(term, "help", "start", "skip", "next", "reset",
+ "visualize", "replay", "log", "run", "terms", NULL))
+ return error(_("can't use the builtin command '%s' as a term"), term);
+
+ /*
+ * In theory, nothing prevents swapping completely good and bad,
+ * but this situation could be confusing and hasn't been tested
+ * enough. Forbid it for now.
+ */
+
+ if ((strcmp(orig_term, "bad") && one_of(term, "bad", "new", NULL)) ||
+ (strcmp(orig_term, "good") && one_of(term, "good", "old", NULL)))
+ return error(_("can't change the meaning of the term '%s'"), term);
+
+ return 0;
+}
+