A Rust procedural macro (proc macro) is a metaprogramming feature in Rust that allows you to define custom syntax extensions and code transformations. They operate on the abstract syntax tree (AST) of Rust code during compilation and can generate or modify code based on annotations or custom syntax.

Sandboxing a Rust proc macro refers to restricting the capabilities of the macro to improve security and prevent potentially harmful code execution. There are several reasons why someone might want to sandbox a proc macro:

1. Security: Untrusted code can be executed during the macro expansion process. To prevent malicious code execution or code that could access sensitive information, sandboxing techniques are employed.

2. Preventing unintended side effects: Some proc macros might inadvertently introduce side effects like file I/O or network requests. Sandboxing can limit these actions to ensure the macro only performs intended transformations.

3. Resource control: To manage system resources, a sandboxed proc macro can be configured to run within resource limits, preventing excessive memory or CPU usage.

4. Isolation: Sandboxing helps keep the macro's execution isolated from the rest of the compilation process, reducing the risk of interfering with other parts of the code.

Sandboxing a Rust proc macro typically involves using crates like sandbox or cap-std to restrict the macro's capabilities and limit its access to the system. This ensures that the macro operates within a controlled environment, enhancing the overall safety of code compilation and execution.

-GPT

I didn't get it either.

Seems to me if your code will be this unpredictable, you should only run it on an air gapped machine