[V4] Fork infrastructure

[ConorWilliams]

Summary by CodeRabbit

• New Features

  • Added context management framework for work scheduling with polymorphic and thread-local variants.
  • Introduced fork and call operation helpers for asynchronous execution.
  • Added TLS-based and global bump allocators for memory management options.

• Improvements

  • Enabled colored build diagnostics output.
  • Extended frame tracking with merge, steal, and exception metadata.

• Refactoring

  • Reorganized core module exports and internal macros.

• Tests

  • Enhanced tuple accessor test coverage across reference qualifications.

[coderabbitai]

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch v4-fork-call

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[coderabbitai]

Actionable comments posted: 2

🤖 Fix all issues with AI agents

In `@benchmark/src/libfork_benchmark/fib/fib.hpp`:
- Around line 86-90: The pop() method currently calls work.back() and
work.pop_back() unconditionally which is undefined if the member vector work is
empty; update lf::work_handle pop() noexcept to defensively check work.empty()
(or assert) before accessing: either add an assertion (e.g.,
assert(!work.empty())) and keep behavior, or return a defined sentinel
lf::work_handle (or std::nullopt-equivalent) when empty; ensure the chosen
approach adjusts the noexcept/specifier and callers of pop() to handle the
sentinel or rely on the assert.

In `@benchmark/src/libfork_benchmark/fib/lf_parts.cpp`:
- Around line 125-127: The leak check currently only compares tls_bump_ptr
against buf.get(), so benchmarks that use the global allocator (e.g.,
no_await<global_bump>, await<global_bump>) that manipulate bump_ptr can leak
undetected; update the check in lf_parts.cpp to verify both tls_bump_ptr and
bump_ptr equal buf.get(), and call LF_TERMINATE("Stack leak detected") (or a
similar error) if either pointer != buf.get() so both thread-local and global
bump allocators are validated.

🧹 Nitpick comments (1)

src/core/context.cxx (1)

17-21: Consider constraining push return type for consistency.

The context concept constrains pop() to return work_handle, but push has no return type constraint. If push should always return void, consider making that explicit for stricter concept checking.

♻️ Optional: Add explicit return type constraint

 template <typename T>
 concept context = requires (T &ctx, work_handle h) {
-  { ctx.push(h) };
+  { ctx.push(h) } -> std::same_as<void>;
   { ctx.pop() } noexcept -> std::same_as<work_handle>;
 };

[Copilot]

Pull request overview

This PR introduces foundational “fork” infrastructure for libfork v4 by adding new core module partitions (ops/context), expanding frame metadata, and updating promise final-suspend logic and benchmarks/tests to exercise the new behavior.

Changes:

• Add libfork.core:ops (call/fork packaging) and libfork.core:context (work handles + TLS context) and wire them into libfork.core/promise.
• Extend coroutine frame metadata (category, cancellation, merge/steal bookkeeping) and update tuple accessor implementation.
• Update benchmarks and tests to use the new root/fork mechanics and new allocators/contexts.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
test/src/tuple.cpp	Adds forced instantiation of tuple accessors; introduces an any helper and extra get<0>() calls.
src/core/utility.cxx	Adds safe_cast, not_null, and a defer scope guard utility.
src/core/tuple.cxx	Adjusts tuple::get implementation to use an explicit cast for cvref propagation.
src/core/promise.cxx	Major update: introduces fork/call awaitables, context integration, and new final_suspend logic.
src/core/ops.cxx	New partition defining exported call()/fork() helpers and internal packages.
src/core/frame.cxx	Adds category enum and expands frame_type with fork-related bookkeeping fields.
src/core/core.cxx	Reorders/tiers module exports and exports new partitions (ops, context).
src/core/context.cxx	New partition defining work_handle, context concept, polymorphic context, and TLS thread_context.
src/core/concepts.cxx	Updates task forward declaration to include a Context parameter.
include/libfork/__impl/assume.hpp	Renames LF_ASSERT to LF_ENSURE and adjusts LF_ASSUME debug behavior.
benchmark/src/libfork_benchmark/fib/lf_parts.cpp	Updates fib benchmarks to mark tasks as root, adds fork/call benchmark variants, and wires TLS context pointers.
benchmark/src/libfork_benchmark/fib/fib.hpp	Replaces old bump allocator with TLS/global bump allocators and adds a vector-backed context implementation.
benchmark/src/libfork_benchmark/fib/baremetal.cpp	Updates baremetal coroutine benchmark to use the new TLS bump allocator pointer.
CMakeUserPresets.json	Enables CMAKE_COLOR_DIAGNOSTICS for dev/bench presets.
CMakeLists.txt	Adds new module sources (ops.cxx, context.cxx) to the build.

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