feat(cli): add entrypoint with --help/--version and exit codes

src/cli.c

@@ -0,0 +1,111 @@
+/*
+ * cli.c - argument parsing for the stupidtools entrypoint.
+ *
+ * Manual parsing on purpose: the flag surface is tiny and fully under
+ * our control, so there is no need for getopt's permutation rules or
+ * its platform quirks. Unknown options are usage errors (exit 2) with
+ * the usage text on stderr; a missing buildfile is a runtime error
+ * (exit 1). -- terminates option parsing so a buildfile whose name
+ * starts with '-' stays addressable.
+ *
+ * Copyright (c) 2026 huntedbytheirs
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include "cli.h"
+
+#include <string.h>
+
+static const char *
+program_name(const char *argv0)
+{
+	if (argv0 == NULL || argv0[0] == '\0') {
+		return "stupidtools";
+	}
+	return argv0;
+}
+
+static int
+is_option(const char *arg)
+{
+	return arg[0] == '-' && arg[1] != '\0' && strcmp(arg, "-") != 0;
+}
+
+void
+cli_print_usage(FILE *stream, const char *program)
+{
+	fprintf(stream,
+	    "Usage: %s [OPTIONS] <buildfile.kdl>\n"
+	    "\n"
+	    "Reads a KDL build file and emits a POSIX-sh ./configure script.\n"
+	    "\n"
+	    "Options:\n"
+	    "  -h, --help     show this help and exit\n"
+	    "  -V, --version  print version and exit\n"
+	    "\n"
+	    "Note: buildfile processing is not yet implemented.\n",
+	    program);
+}
+
+/* Take the next positional argument, reporting usage errors to stderr.
+ * Returns CLI_ACTION_ERROR (with usage printed) or CLI_ACTION_RUN. */
+static enum cli_action
+take_positional(const char *arg, struct cli_opts *opts)
+{
+	if (opts->buildfile != NULL) {
+		fprintf(stderr, "%s: unexpected extra argument '%s'\n",
+		    opts->program, arg);
+		cli_print_usage(stderr, opts->program);
+		return CLI_ACTION_ERROR;
+	}
+	opts->buildfile = arg;
+	return CLI_ACTION_RUN;
+}
+
+enum cli_action
+cli_parse(int argc, char **argv, struct cli_opts *opts)
+{
+	enum cli_action action;
+	int i;
+
+	opts->program = program_name(argc > 0 ? argv[0] : NULL);
+	opts->buildfile = NULL;
+
+	for (i = 1; i < argc; i++) {
+		const char *arg = argv[i];
+
+		if (!is_option(arg)) {
+			action = take_positional(arg, opts);
+			if (action != CLI_ACTION_RUN) {
+				return action;
+			}
+			continue;
+		}
+
+		if (strcmp(arg, "--") == 0) {
+			for (i++; i < argc; i++) {
+				action = take_positional(argv[i], opts);
+				if (action != CLI_ACTION_RUN) {
+					return action;
+				}
+			}
+			break;
+		}
+
+		if (strcmp(arg, "-h") == 0 || strcmp(arg, "--help") == 0) {
+			cli_print_usage(stdout, opts->program);
+			return CLI_ACTION_HELP;
+		}
+
+		if (strcmp(arg, "-V") == 0 || strcmp(arg, "--version") == 0) {
+			return CLI_ACTION_VERSION;
+		}
+
+		fprintf(stderr, "%s: unrecognized option '%s'\n",
+		    opts->program, arg);
+		cli_print_usage(stderr, opts->program);
+		return CLI_ACTION_ERROR;
+	}
+
+	return CLI_ACTION_RUN;
+}