fuzzer and performance optimisations

tests/fuzz_config.cpp

@@ -0,0 +1,39 @@
+// fuzz_config.cpp - libFuzzer harness for the .rc parser.
+//
+// Built and driven by tools/fuzz.py with clang++ -fsanitize=fuzzer. The
+// parser is exercised on raw bytes through the same `parse_rc_stream` path
+// used by the real init. `@import` is rejected inside the harness (the
+// opener throws) so fuzz input can never open real files such as /dev/zero.
+#include "../src/config.cpp"
+
+#include <cstddef>
+#include <cstdint>
+#include <memory>
+#include <sstream>
+#include <string>
+#include <vector>
+
+namespace {
+
+struct NoImports {
+    std::unique_ptr<std::istream> operator()(const std::string&) const {
+        throw std::runtime_error("fuzz: @import disabled");
+    }
+};
+
+} // namespace
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+    const std::string text(reinterpret_cast<const char*>(data), size);
+    bajia::Config cfg;
+    std::vector<std::string> chain;
+    std::vector<std::string> seen;
+    try {
+        std::istringstream in(text);
+        bajia::parse_rc_stream(cfg, in, "/fuzz/main.rc", chain, seen,
+                               NoImports{});
+    } catch (const std::exception&) {
+        // every parse error is a valid outcome; crashes are the bugs.
+    }
+    return 0;
+}