Add two draft project goals: seamless C support, and relaxing the orphan rule

src/2024h2/Relaxing-the-Orphan-Rule.md

@@ -0,0 +1,132 @@
+# Relaxing the Orphan Rule
+
+| Metadata | |
+| --- | --- |
+| Owner(s) | |
+| Teams | *lang* |
+| Status | WIP |
+
+## Motivation
+
+Relax the orphan rule, in limited circumstances, to allow crates to provide
+implementations of third-party traits for third-party types. The orphan rule
+averts one potential source of conflicts between Rust crates, but its presence
+also creates scaling issues in the Rust community: it prevents providing a
+third-party library that integrates two other libraries with each other, and
+instead requires convincing the author of one of the two libraries to add
+(optional) support for the other, or requires using a newtype wrapper. Relaxing
+the orphan rule, carefully, would make it easier to integrate libraries with
+each other, share those integrations, and make it easier for new libraries to
+garner support from the ecosystem.
+
+### The status quo
+
+Suppose a Rust developer wants to work with two libraries: `lib_a` providing
+trait `TraitA`, and `lib_b` providing type `TypeB`. Due to the orphan rule, if
+they want to use the two together, they have the following options:
+
+- Convince the maintainer of `lib_a` to provide `impl TraitA for TypeB`. This
+  typically involves an optional dependency on `lib_b`. This usually only
+  occurs if `lib_a` is substantially less popular than `lib_b`, or the
+  maintainer of `lib_a` is convinced that others are likely to want to use the
+  two together. This tends to feel "reversed" from the norm.
+
+- Convince the maintainer of `lib_b` to provide `impl TraitA for TypeB`. This
+  typically involves an optional dependency on `lib_a`. This is only likely to
+  occur if `lib_a` is popular, and the maintainer of `lib_b` is convinced that
+  others may want to use the two together. The difficulty in advocating this,
+  scaled across the community, is one big reason why it's difficult to build
+  new popular crates built around traits (e.g. competing
+  serialization/deserialization libraries, or competing async I/O traits).
+
+- Vendor either `lib_a` or `lib_b` into their own project. This is
+  inconvenient, adds maintenance costs, and isn't typically an option for
+  public projects intended for others to use.
+
+- Create a newtype wrapper around `TypeB`, and implement `TraitA` for the
+  wrapper type. This is less convenient, propagates throughout the crate (and
+  through other crates if doing this in a library), and may require additional
+  trait implementations for the wrapper that `TypeB` already implemented.
+
+All of these solutions are suboptimal in some way, and inconvenient. In
+particular, all of them are much more difficult than actually writing the trait
+impl. All of them tend to take longer, as well, slowing down whatever goal
+depended on having the trait impl.
+
+### The next few steps
+
+As an initial experiment, try relaxing the orphan rule for binary crates, since
+this cannot create library incompatibilities in the ecosystem. Allow binary
+crates to implement third-party traits for third-party types, possibly
+requiring a marker on either the trait or type or both. See how well this works
+for users.
+
+As a second experiment, try allowing library crates to provide third-party
+impls as long as no implementations actually conflict. Perhaps require marking
+traits and/or types that permit third-party impls, to ensure that crates can
+always implement traits for their own types.
+
+### The "shiny future" we are working towards
+
+Long-term, we'll want a way to resolve conflicts between third-party trait
+impls.
+
+We should support a "standalone derive" mechanism, to derive a trait for a type
+without attaching the derive to the type definition. We could save a simple
+form of type information about a type, and define a standalone deriving
+mechanism that consumes exclusively that information.
+
+Given such a mechanism, we could then permit any crate to invoke the standalone
+derive mechanism for a trait and type, and allow identical derivations no
+matter where they appear in the dependency tree.
+
+## Design axioms
+
+- **Rustaceans should be able to easily integrate a third-party trait with a
+  third-party type without requiring the cooperation of third-party crate
+  maintainers.**
+
+- **It should be possible to *publish* such integration as a new crate.** For
+  instance, it should be possible to publish an `a_b` crate integrating `a`
+  with `b`. This makes it easier to scale the ecosystem and get adoption for
+  new libraries.
+
+- **Crate authors should have some control over whether their types have
+  third-party traits implemented.** This ensures that it isn't a breaking
+  change to introdice first-party trait implementations.
+
+[da]: ../about/design_axioms.md
+
+## Ownership and other resources
+
+**Owner:** TODO
+
+### Support needed from the project
+
+* Lang team:
+    * Design meetings to discuss design changes
+    * RFC reviews
+* Blog post inviting testing, evaluation, and feedback
+
+## Outputs and milestones
+
+### Outputs
+
+The output will be a pair of RFCs:
+- A lang RFC proposing a very simple system for binaries to ignore the orphan rule.
+- A lang RFC proposing a system with more careful safeguards, to relax the orphan rule for publishable library crates.
+
+### Milestones
+
+- Accepted RFCs.
+
+## Frequently asked questions
+
+### Won't this create incompatibilities between libraries that implement the same trait for the same type?
+
+Yes! The orphan rule is a tradeoff. It was established to avert one source of
+potential incompatibility between library crates, in order to help the
+ecosystem grow, scale, and avoid conflicts. However, the presence of the orphan
+rule creates a different set of scaling issues and conflicts. This project goal
+proposes to adjust the balance, attempting to achieve some of the benefits of
+both.

src/2024h2/Seamless-C-Support.md

@@ -0,0 +1,137 @@
+# Seamless C support
+
+| Metadata | |
+| --- | --- |
+| Owner(s) | *Github usernames or other identifying info for goal owners* |
+| Teams | *Names of teams being asked to commit to the goal* |
+| Status | WIP |
+
+## Motivation
+
+Using C from Rust should be as easy as using C from C++: completely seamless,
+as though it's just another module of code. You should be able to drop Rust
+code into a C project and start compiling and using it in minutes.
+
+### The status quo
+
+Today, people who want to use C and Rust together in a project have to put
+substantial work into infrastructure or manual bindings. Whether by creating
+build system infrastructure to invoke bindgen/cbindgen (and requiring the
+installation of those tools), or manually writing C bindings in Rust, projects
+cannot simply drop Rust code into a C program or C code into a Rust program.
+This creates a high bar for adopting or experimenting with Rust, and makes it
+more difficult to provide Rust bindings for a C library.
+
+By contrast, dropping C++ code into a C project or C code into a C++ project is
+trivial. The same compiler understands both C and C++, and allows compiling
+both together or separately. The developer does not need to duplicate
+declarations for the two languages, and can freely call between functions in
+both languages.
+
+C and C++ are still not the same language. They have different idioms and
+common types, and a C interface may not be the most ergonomic to use from C++.
+Using C++ from C involves treating the C as C++, such that it no longer works
+with a C compiler that has no C++ support. But nonetheless, C++ and C integrate
+extremely well, and C++ is currently the easiest language to integrate into an
+established C project.
+
+This is the level of integration we should aspire to for Rust and C.
+
+### The next few steps
+
+To provide seamless integration between Rust and C, we need a single compiler
+to understand both Rust and C. Thus, the first step will be to integrate a C
+preprocessor and compiler frontend into the Rust compiler. For at least the
+initial experimentation, we could integrate components from LLVM, taking
+inspiration from `zig cc`. (In the future, we can consider other alternatives,
+including a native Rust implementation. We could also consider components from
+c2rust or similar.)
+
+We can either generate MIR directly from C (which would be experimental and
+incomplete but integrate better with the compiler), or bypass MIR and generate
+LLVM bytecode (which would be simpler but less well integrated).
+
+This first step would provide substantial benefits already: a C compiler that's
+always available on any system with Rust installed, that generates code for any
+supported Rust target, and that always supports cross-language optimization.
+
+We can further improve support for calling C from Rust. We can support
+"importing" C header files, to permit using this support to call external
+libraries, and to support inline functions.
+
+### The "shiny future" we are working towards
+
+Once C support is integrated, we can generate type information for C functions
+as if they were unsafe Rust functions, and then support treating the C code as
+a Rust module, adding the ability to import and call C functions from Rust.
+This would not necessarily even require header files, making it even simpler to
+use C from Rust. The initial support can be incomplete, supporting the subset
+of C that has reasonable semantics in Rust.
+
+We will also want to add C features that are missing in Rust, to allow Rust to
+call any supported C code.
+
+Once we have a C compiler integrated into Rust, we can incrementally add C
+extensions to support using Rust from C. For instance:
+- Support importing Rust modules and calling `extern "C"` functions from
+  them, without requiring a C header file.
+- Support using `::` for scoping names.
+- Support simple Rust types (e.g. `Option` and `Result`).
+- Support calling Rust methods on objects.
+- Allow annotating C functions with Rust-enhanced type signatures, such as
+  marking them as safe, using Rust references for pointer parameters, or
+  providing simple lifetime information.
+
+We can support mixing Rust and C in a source file, to simplify incremental
+porting even further.
+
+To provide simpler integration into C build systems, we can accept a
+C-compiler-compatible command line (`CFLAGS`), and apply that to the C code we
+process.
+
+We can also provide a CLI entry point that's sufficiently command-line
+compatible to allow using it as `CC` in a C project.
+
+## Design axioms
+
+- **C code should feel like just another Rust module.** Integrating C code into
+  a Rust project, or Rust code into a C project, should be trivial; it should
+  be just as easy as integrating C with C++.
+
+- **This is not primarily about providing *safe* bindings.** This project will
+  primarily make it much easier to access C bindings as unsafe interfaces.
+  There will still be value in wrapping these unsafe C interfaces with safer
+  Rust interfaces.
+
+- **Calling C from Rust should not require writing duplicate information in Rust**
+  that's already present in a C header or source file.
+
+- **Integrating C with Rust should not require third-party tools**.
+
+- **Compiling C code should not require substantially changing the information
+  normally passed to a C compiler** (e.g. compiler arguments).
+
+## Ownership and other resources
+
+**Owner:** TODO
+
+### Support needed from the project
+
+* Lang team:
+  * Design meetings to discuss design changes
+  * RFC reviews
+* Compiler team:
+  * RFC review
+
+## Outputs and milestones
+
+### Outputs
+
+The initial output will be a pair of RFCs: one for an experimental integration of a C compiler into rustc, and the other for minimal language features to take advantage of that.
+
+### Milestones
+
+- Compiler RFC: Integrated C compiler
+- Lang RFC: Rust language support for seamless C integration
+
+## Frequently asked questions

src/2024h2/slate.md

@@ -31,6 +31,8 @@ None
 | ↳ [Fallible allocation][]           | ![Owner needed][own]      |                    |
 | [Polonius on nightly][]             | [lqd]                     | [Lang], [Types]    |
 | [Impl trait everywhere][]           | [oli-obk]                 | [Lang], [Types]    |
+| [Seamless C Support][]              | ![Owner needed][own]      | [Lang]             |
+| [Relaxing the Orphan Rule][]        | ![Owner needed][own]      | [Lang]             |
 
 ## Not accepted goals
 
@@ -48,6 +50,8 @@ None.
 [Return type notation]: ./Async--AsyncClosures.md
 [Polonius on nightly]: ./Polonius.md
 [Impl trait everywhere]: ./Impl-trait-everywhere.md
+[Seamless C Support]: ./Seamless-C-Support.md
+[Relaxing the Orphan Rule]: ./Relaxing-the-Orphan-Rule.md
 
 [own]: https://img.shields.io/badge/Owned%20Needed-blue
 
@@ -60,4 +64,4 @@ None.
 [LC]: https://www.rust-lang.org/governance/teams/leadership-council
 [Lang]: https://www.rust-lang.org/governance/teams/lang
 [Types]: https://www.rust-lang.org/governance/teams/compiler#team-types
-[Libs-API]: https://www.rust-lang.org/governance/teams/library#team-libs-api
+[Libs-API]: https://www.rust-lang.org/governance/teams/library#team-libs-api