The Axon compiler (axonc) processes untrusted source code input. As a language compiler, it accepts arbitrary user-written programs and must handle malformed, adversarial, or pathological inputs safely without crashing, leaking memory, or producing undefined behavior in the compiler itself.

1. Lexer — Rejects invalid tokens, unterminated strings, and malformed numeric literals with clear error messages.
2. Parser — Validates syntax against the Axon grammar. Malformed input produces structured CompileError diagnostics rather than panics.
3. Type Checker — Prevents type-unsafe operations through static analysis. Enforces type unification with occurs-check to prevent infinite types.
4. Borrow Checker — Enforces Rust-inspired ownership and borrowing rules to prevent use-after-move, double-free, and data race conditions in user programs.
5. Shape Checker — Validates tensor dimension compatibility at compile time, preventing shape mismatch errors that would occur at runtime.

The Axon compiler includes fuzzing targets in the fuzz/ directory:

• Parser fuzzer (fuzz/fuzz_targets/fuzz_parser.rs) — Feeds arbitrary byte sequences to the parser to ensure it never panics on any input.
• Type checker fuzzer (fuzz/fuzz_targets/fuzz_typeck.rs) — Feeds arbitrary source to the full compilation pipeline (parse → type-check → borrow-check) to ensure robustness.

These fuzz targets are designed for use with cargo-fuzz (libFuzzer backend) and can be run with:

cargo fuzz run fuzz_parser
cargo fuzz run fuzz_typeck

• All compiler errors use structured types (CompileError) rather than string formatting, preventing information leakage.
• The compiler never executes user code during compilation (execution happens only in the REPL's type-evaluation mode, which does not evaluate at runtime).
• LLVM code generation produces well-formed IR; the LLVM backend provides additional validation.
• CI runs cargo clippy and cargo test on every pull request.

If you discover a security vulnerability in the Axon compiler, please report it responsibly:

1. Do not open a public GitHub issue for security vulnerabilities.
2. Email: Send a detailed report to the project maintainers with:
   • Description of the vulnerability
   • Steps to reproduce (ideally a minimal .axon source file)
   • Expected vs. actual behavior
   • Impact assessment
3. Response time: We aim to acknowledge reports within 48 hours and provide a fix or mitigation within 7 days for critical issues.

The Axon compiler does not require any special security configuration. It operates as a command-line tool with no network access, no file system writes (except for output files explicitly requested by the user), and no execution of user code during compilation.