Function string_realise 

pub unsafe extern "C" fn string_realise(
    context: *mut c_context,
    state: *mut EvalState,
    value: *mut value,
    isIFD: bool,
) -> *mut realised_string

@brief Realise a string context.

This will

• realise the store paths referenced by the string’s context, and
• perform the replacement of placeholders.
• create temporary garbage collection roots for the store paths, for the lifetime of the current process.
• log to stderr

@param[out] context Optional, stores error information @param[in] value Nix value, which must be a string @param[in] state Nix evaluator state @param[in] isIFD If true, disallow derivation outputs if setting allow-import-from-derivation is false. You should set this to true when this call is part of a primop. You should set this to false when building for your application’s purpose. @return NULL if failed, or a new nix_realised_string, which must be freed with nix_realised_string_free