codegen_traits.rs

// Protocol Buffers - Google's data interchange format
// Copyright 2024 Google LLC.  All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd

//! Traits that are implemented by codegen types.

use crate::__internal::SealedInternal;
use crate::{MutProxied, MutProxy, ViewProxy};
use create::Parse;
use interop::{MessageMutInterop, MessageViewInterop, OwnedMessageInterop};
use read::Serialize;
use std::fmt::Debug;
use write::{Clear, ClearAndParse, CopyFrom, MergeFrom, TakeFrom};

/// A trait that all generated owned message types implement.
pub trait Message: SealedInternal
  + MutProxied
  // Create traits:
  + Parse + Default
  // Read traits:
  + Debug + Serialize
  // Write traits:
  + Clear + ClearAndParse + TakeFrom + CopyFrom + MergeFrom
  // Thread safety:
  + Send + Sync
  // Copy/Clone:
  + Clone
  // C++ Interop:
  + OwnedMessageInterop
{
}

/// A trait that all generated message views implement.
pub trait MessageView<'msg>: SealedInternal
    + ViewProxy<'msg, Proxied = Self::Message>
    // Read traits:
    + Debug + Serialize + Default
    // Thread safety:
    + Send + Sync
    // Copy/Clone:
    + Copy + Clone
    // C++ Interop:
    + MessageViewInterop<'msg>
{
    #[doc(hidden)]
    type Message: Message;
}

/// A trait that all generated message muts implement.
pub trait MessageMut<'msg>: SealedInternal
    + MutProxy<'msg, MutProxied = Self::Message>
    // Read traits:
    + Debug + Serialize
    // Write traits:
    + Clear + ClearAndParse + TakeFrom + CopyFrom + MergeFrom
    // Thread safety:
    + Sync
    // Copy/Clone:
    // (Neither)
    // C++ Interop:
    + MessageMutInterop<'msg>
{
    #[doc(hidden)]
    type Message: Message;
}

/// Operations related to constructing a message. Only owned messages implement
/// these traits.
pub(crate) mod create {
    use super::SealedInternal;
    pub trait Parse: SealedInternal + Sized {
        fn parse(serialized: &[u8]) -> Result<Self, crate::ParseError>;
    }
}

/// Operations related to reading some aspect of a message (methods that would
/// have a `&self` receiver on an owned message). Owned messages, views, and
/// muts all implement these traits.
pub(crate) mod read {
    use super::SealedInternal;

    pub trait Serialize: SealedInternal {
        fn serialize(&self) -> Result<Vec<u8>, crate::SerializeError>;
    }
}

/// Operations related to mutating a message (methods that would have a `&mut
/// self` receiver on an owned message). Owned messages and muts implement these
/// traits.
pub(crate) mod write {
    use super::SealedInternal;
    use crate::{AsMut, AsView};

    pub trait Clear: SealedInternal {
        fn clear(&mut self);
    }

    pub trait ClearAndParse: SealedInternal {
        fn clear_and_parse(&mut self, data: &[u8]) -> Result<(), crate::ParseError>;
    }

    /// Copies the contents from `src` into `self`.
    ///
    /// This is a copy in the sense that `src` message is not mutated and `self` will have
    /// the same state as `src` after this call; it may not be a bitwise copy.
    pub trait CopyFrom: AsView + SealedInternal {
        fn copy_from(&mut self, src: impl AsView<Proxied = Self::Proxied>);
    }

    /// Moves the contents from `src` into `self`.
    ///
    /// Any previous state of `self` is discarded, and if `src` is still observable then it is
    /// guaranteed to be in its default state after this call. If `src` is a field on a parent
    /// message, the presence of that field will be unaffected.
    pub trait TakeFrom: AsView + SealedInternal {
        fn take_from(&mut self, src: impl AsMut<MutProxied = Self::Proxied>);
    }

    pub trait MergeFrom: AsView + SealedInternal {
        fn merge_from(&mut self, src: impl AsView<Proxied = Self::Proxied>);
    }
}

/// Traits related to interop with C or C++.
///
/// These traits are deliberately not available on the prelude, as they should
/// be used rarely and with great care.
pub(crate) mod interop {
    use super::SealedInternal;
    use std::ffi::c_void;

    /// Traits related to owned message interop. Note that these trait fns
    /// are only available on C++ kernel as upb interop of owned messages
    /// requires more work to handle the Arena behavior.
    pub trait OwnedMessageInterop: SealedInternal {
        /// Drops `self` and returns an underlying pointer that it was wrapping
        /// without deleting it.
        ///
        /// The caller is responsible for ensuring the returned pointer is
        /// subsequently deleted (eg by moving it into a std::unique_ptr in
        /// C++), or else it will leak.
        #[cfg(cpp_kernel)]
        fn __unstable_leak_raw_message(self) -> *mut c_void;

        /// Takes exclusive ownership of the `raw_message`.
        ///
        /// # Safety
        ///   - The underlying message must be for the same type as `Self`
        ///   - The pointer passed in must not be used by the caller after being
        ///     passed here (must not be read, written, or deleted)
        #[cfg(cpp_kernel)]
        unsafe fn __unstable_take_ownership_of_raw_message(raw_message: *mut c_void) -> Self;
    }

    /// Traits related to message view interop.
    pub trait MessageViewInterop<'msg>: SealedInternal {
        /// Borrows `self` as an underlying C++ raw pointer.
        ///
        /// Note that the returned Value must be used under the same constraints
        /// as though it were a borrow of `self`: it should be treated as a
        /// `const Message*` in C++, and not be mutated in any way, and any
        /// mutation to the parent message may invalidate it, and it
        /// must not be deleted.
        fn __unstable_as_raw_message(&self) -> *const c_void;

        /// Wraps the provided pointer as a MessageView.
        ///
        /// This takes a ref of a pointer so that a stack variable's lifetime
        /// can be used for a safe lifetime; under most cases this is
        /// the correct lifetime and this should be used as:
        /// ```ignore
        /// fn called_from_cpp(msg: *const c_void) {
        ///   // `msg` is known live for the current stack frame, so view's
        ///   // lifetime is also tied to the current stack frame here:
        ///   let view = unsafe { __unstable_wrap_raw_message(&msg) };
        ///   do_something_with_view(view);
        /// }
        /// ```
        ///
        /// # Safety
        ///   - The underlying message must be for the same type as `Self`
        ///   - The underlying message must be alive for 'msg and not mutated
        ///     while the wrapper is live.
        unsafe fn __unstable_wrap_raw_message(raw: &'msg *const c_void) -> Self;

        /// Wraps the provided pointer as a MessageView.
        ///
        /// Unlike `__unstable_wrap_raw_message` this has no constraints
        /// on lifetime: the caller has a free choice for the lifetime.
        ///
        /// As this is much easier to get the lifetime wrong than
        /// `__unstable_wrap_raw_message`, prefer using that wherever
        /// your lifetime can be tied to a stack lifetime, and only use this one
        /// if its not possible (e.g. with a 'static lifetime).
        ///
        /// # Safety
        ///   - The underlying message must be for the same type as `Self`
        ///   - The underlying message must be alive for the caller-chosen 'msg
        ///     and not mutated while the wrapper is live.
        unsafe fn __unstable_wrap_raw_message_unchecked_lifetime(raw: *const c_void) -> Self;
    }

    /// Traits related to message mut interop. Note that these trait fns
    /// are only available on C++ kernel as upb interop of owned messages
    /// requires more work to handle the Arena behavior.
    pub trait MessageMutInterop<'msg>: SealedInternal {
        /// Exclusive borrows `self` as an underlying mutable C++ raw pointer.
        ///
        /// Note that the returned Value must be used under the same constraints
        /// as though it were a mut borrow of `self`: it should be treated as a
        /// non-owned `Message*` in C++. And any mutation to the parent message
        /// may invalidate it, and it must not be deleted.
        #[cfg(cpp_kernel)]
        fn __unstable_as_raw_message_mut(&mut self) -> *mut c_void;

        /// Wraps the provided C++ pointer as a MessageMut.
        ///
        /// This takes a ref of a pointer so that a stack variable's lifetime
        /// can be used for a safe lifetime; under most cases this is
        /// the correct lifetime and this should be used as:
        /// ```ignore
        /// fn called_from_cpp(msg: *mut c_void) {
        ///   // `msg` is known live for the current stack frame, so mut's
        ///   // lifetime is also tied to the current stack frame here:
        ///   let m = unsafe { __unstable_wrap_raw_message_mut(&mut msg) };
        ///   do_something_with_mut(m);
        /// }
        /// ```
        ///
        /// # Safety
        ///   - The underlying message must be for the same type as `Self`
        ///   - The underlying message must be alive for 'msg and not read or
        ///     mutated while the wrapper is live.
        #[cfg(cpp_kernel)]
        unsafe fn __unstable_wrap_raw_message_mut(raw: &'msg mut *mut c_void) -> Self;

        /// Wraps the provided pointer as a MessageMut.
        ///
        /// Unlike `__unstable_wrap_raw_message_mut` this has no constraints
        /// on lifetime: the caller has a free choice for the lifetime.
        ///
        /// As this is much easier to get the lifetime wrong than
        /// `__unstable_wrap_raw_message_mut`, prefer using that wherever
        /// the lifetime can be tied to a stack lifetime, and only use this one
        /// if its not possible (e.g. with a 'static lifetime).
        ///
        /// # Safety
        ///   - The underlying message must be for the same type as `Self`
        ///   - The underlying message must be alive for the caller-chosen 'msg
        ///     and not mutated while the wrapper is live.
        #[cfg(cpp_kernel)]
        unsafe fn __unstable_wrap_raw_message_mut_unchecked_lifetime(raw: *mut c_void) -> Self;
    }
}