POC: Embedded Swift consumers of dispatch on wasm32-unknown-wasip1 - #7
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POC: Embedded Swift consumers of dispatch on wasm32-unknown-wasip1#7scottmarchant wants to merge 4 commits into
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Two gated changes make all nine overlay files compile with -enable-experimental-feature Embedded, with no API removed and no signature moved: - Import _DispatchOverlayShims plainly under #if hasFeature(Embedded). Embedded Swift compiles public functions into the client, so an @_implementationOnly import is unusable from them (56 errors). - Constrain DispatchSourceProtocol through a conditional typealias that is AnyObject under Embedded and Any elsewhere. Embedded Swift only supports class-bound existentials, and the make*Source factories return them (14 errors). The only conformer is the DispatchSource class, so the bound is factual. Non-embedded arms are unchanged: the cooperative WASI suite still passes 52 of 52 with these edits. Co-authored-by: Krzysztof Rodak <krodak.konta@gmail.com> Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
cmake ... -DDISPATCH_WASI_EMBEDDED=ON -DENABLE_SWIFT=YES builds libdispatch.a, libBlocksRuntime.a, and libswiftDispatch.a in Embedded Swift mode. The knob appends -enable-experimental-feature Embedded, selects usr/lib/swift as the Swift resource dir (the embedded stdlib modules live there), forces CMAKE_Swift_COMPILATION_MODE=wholemodule and propagates it through try_compile (or the compiler check runs incrementally and reports the compiler as broken), and defines __EMBEDDED_SWIFT__ on the C side to match the SDK's embedded toolset. The C library produced with the knob is the cooperative port, unchanged. The regular configuration is unaffected: the cooperative suite still passes 52 of 52 after a reconfigure. Co-authored-by: Krzysztof Rodak <krodak.konta@gmail.com> Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Add tests/wasm/embedded-dispatch-smoke.swift, an Embedded Swift
consumer of the overlay built in embedded mode. Under wasmtime v24
LTS and current wasmtime v47 it prints:
PASS: async=8/8 sync=1 group=1 timer=1 source=1 data=4
Coverage: eager async on the cooperative backend, serial sync,
DispatchGroup wait, a dispatch_after timer firing while a semaphore
wait pumps, a timer DispatchSource through the class-bound existential
path, and DispatchData append/iterate through the shims funnel. The
same source builds to 572 KB embedded vs 7.8 MB with the regular
static-stdlib SDK.
Co-authored-by: Krzysztof Rodak <krodak.konta@gmail.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Add tests/wasm/EMBEDDED-RESEARCH.md: the official swift.org embedded wasm SDK shares the wasm32-unknown-wasip1 triple and sysroot with the regular SDK and differs only in toolset flags, so the C library and the cooperative event backend need zero changes. Record the toolchain facts that cost time: the host toolchain lacks wasm compiler-rt builtins (override the clang resource dir), Embedded Swift emits no autolink metadata (consumers must name every archive), whole-module mode is mandatory, and wasi-libc clockid macros do not import. Co-authored-by: Krzysztof Rodak <krodak.konta@gmail.com> Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Fork-only proof of concept. This PR is a draft on purpose and is not meant to merge. It shows the Embedded Swift research on top of #3 (the combined WASI port). The full findings live in
tests/wasm/EMBEDDED-RESEARCH.mdon this branch. The series tracker is #3.Summary
An Embedded Swift program can import Dispatch and use it today, with the official swift.org
swift-6.3.3-RELEASE_wasm-embeddedSDK. The smoke test dispatches work, waits on semaphores and groups, arms a timer source, and walks aDispatchData. It passes under both wasmtime v24 LTS and current wasmtime v47 (the output is a plain wasip1 module, so there is no runtime constraint):Binary size is the headline: the same consumer builds to 572 KB embedded vs 7.8 MB with the regular static-stdlib SDK, about 13.6x smaller. The cooperative suite still passes 52 of 52 with these edits.
What this dictates for #3 and #5
@_implementationOnly) shims import under#if hasFeature(Embedded), and a class bound onDispatchSourceProtocolthrough a conditional typealias (AnyObjectunder Embedded,Anyelsewhere). The typealias is the one cross-platform-visible addition; an upstream reviewer may prefer a different spelling.Discoveries specific to embedded
linkdirectives in the module maps are ignored, so consumers must name every archive on the link line. The regular SDK autolinks them.CMAKE_Swift_COMPILATION_MODE=wholemodule, and it must be propagated intotry_compileor the Swift compiler check fails.-Xclang-linker -resource-dir ...).CLOCK_MONOTONICis a pointer macro to an incomplete struct and does not import into Embedded Swift. The overlay is unaffected (it funnels through the C shims); consumer code that uses raw libc clocks will notice.DISPATCH_WASI_EMBEDDED=ONbuilds libdispatch.a, libBlocksRuntime.a, and libswiftDispatch.a in embedded mode.BUILD_TESTINGstays OFF: an embedded ctest lane is future work.Commits
Four conventional commits: the two overlay edits, the CMake knob, the smoke test, and the research notes.