Macro file_err 

macro_rules! file_err {
    ($path:expr, read) => { ... };
    ($path:expr, write) => { ... };
    ($path:expr, delete) => { ... };
    ($path:expr, create) => { ... };
}

Helper macro for file operation errors with context.

Usage: file_err!(path, read) where path is an expression and the operation is matched as a bare identifier (not a string literal). Expands to "failed to read <path>".