Macro seal 

seal!() { /* proc-macro */ }

Seal macro that prevents accidental modification of the enclosed source code by hashing the source code and comparing it to the supplied hash. If the code is modified, the macro will fail to compile, and the developer will need to change the hash value. This is useful for locking down sensitive parts of the code to prevent their accidental change. Wraps a code block with a content hash seal, taking a seal id and a code block (seal!(0x1234, { ... })). The macro emits the block plus a SEAL constant and fails to compile if the block’s content no longer matches the supplied seal id, drawing attention to changes in security-sensitive code.