This commit compares the decl inside the `@abi` attribute to the decl it’s attached to, diagnosing ABI-incompatible differences. It does not yet cover attributes, which are a large undertaking.
* Revert "[CSOptimizer] Look through `OptionalEvaluationExpr`s when dealing with unapplied disjunctions"
This reverts commit 72340f39b8.
* Revert "[CSOptimizer] Don't consider disabled overloads when checking whether disjunction is supported"
This reverts commit 6bc23b5057.
* Revert "[CSOptimizer] Disjunctions with IUO overload choices are unsupported"
This reverts commit 471ee21535.
* Revert "[CSOptimizer] MemberImportVisibility: Don't consider overloads that come from implicit imports"
This reverts commit aa4a2b9071.
* Revert "[CSOptimizer] Don't consider CGFloat widening when explicit initializer is used"
This reverts commit 3cc76eacdd.
* Revert "[CSOptimizer] Literal arguments should cause score reset only for operators"
This reverts commit e3987beffb.
* Revert "[CSOptimizer] NFC: check whether a choice is of operator instead of whole disjunction"
This reverts commit 6c82892c3c.
* Revert "[CSOptimizer/Tests] NFC: Add a perf test-case fixed by improved literal array handling"
This reverts commit cfd34e54c4.
* Revert "[CSOptimizer] Extend candidate/parameter matching to support array literals"
This reverts commit 8a304f88c6.
* Revert "[CSOptimizer] Favor choices that don't require application"
This reverts commit 0737542da8.
* Revert "[CSOptimizer] Disable CGFloat -> Double conversion for unary operators"
This reverts commit bc3a15fbe6.
* Revert "[CSOptimizer] Mark bitwise operators as supported"
This reverts commit 860ae08d1b.
* Revert "[CSOptimizer] Simplify handling of non-applied disjunctions"
This reverts commit 43ca7dfff9.
* Revert "[ConstraintSystem] Fix `getEffectiveOverloadType` handling of `mutating` methods"
This reverts commit c767f7aff7.
* Revert "[CSOptimizer] Reduce overload types before ranking"
This reverts commit 95b47aead6.
* Revert "[CSOptimizer] Implement special prioritization rules for result builder contexts"
This reverts commit 56d6635e46.
* Revert "[CSOptimizer] Allow only widening CGFloat->Double conversions while matching candidate arguments"
This reverts commit bf8ae3bc1b.
* Revert "[CSSimplify] CGFloat-Double: Rank narrowing correctly when result is injected into an optional"
This reverts commit cb876cbd9e.
* Revert "[CSBindings] Prevent `BindingSet::isViable` from dropping viable bindings (v2)"
This reverts commit b7e7493076.
* Revert "[CSOptimizer] Add support for chained members without arguments"
This reverts commit 87cd5f8733.
* Revert "[CSOptimizer] Mark compiler synthesized disjunctions as optimized"
This reverts commit 867e64182f.
* Revert "[CSOptimizer] Make a light-weight generic overload check if some requirements are unsatisfiable"
This reverts commit 15c773b9d7.
* Revert "[CSOptimizer] Fix `selectDisjunction` to use favored choices even if disjunction was not optimized"
This reverts commit c2a55886f0.
* Revert "[CSOptimizer] Limit "old" behavior compatibility to unlabeled unary arguments"
This reverts commit 9fb73143f6.
* Revert "[Tests] NFC: Update a couple of type-checker tests"
This reverts commit ff8663ff16.
* Revert "[Tests] NFC: Move simd related test-case from `slow` to `fast`"
This reverts commit 28396a6dce.
* Revert "[CSGen] NFC: Remove obsolete `ConstraintSystem::{get, set}FavoredType`"
This reverts commit 8bd288447f.
* Revert "[CSOptimizer] Allow literal arguments to match parameters that conform to `ExpressibleBy{Integer, Float}Literal`"
This reverts commit 2fdd4b6c35.
* Revert "[CSOptimizer] Adjust `scoreCandidateMatch` to indicate when match cannot be decided"
This reverts commit 9b62c84a4f.
* Revert "[CSOptimizer] Fix Double<->CGFloat implicit conversion support when arguments are literals"
This reverts commit 6caf1ccbb2.
* Revert "[CSOptimizer] A more comprehensive generic overload checking when candidates are fully resolved"
This reverts commit e30587bda4.
* Revert "[CSOptimizer] Restore old hack behavior which used to favor overloads based on arity matches"
This reverts commit a3a3ec4fe0.
* Revert "[CSOptimizer] Desugar types before checking for equality"
This reverts commit 802f5cd105.
* Revert "[ConstraintSystem] Narrowly disable `tryOptimizeGenericDisjunction` when some of the arguments are number literals"
This reverts commit 8d5cb112ef.
* Revert "[CSOptimizer] Infer argument candidates from calls to `Double` and CGFloat constructors"
This reverts commit f2a6677a6d.
* Revert "[CSOptimizer] Score all of the overload choices matching on literals uniformly"
This reverts commit 59109c2d60.
* Revert "[CSOptimizer] Enable ranking of `Int*`, `Float{80}` and `Double` initializers"
This reverts commit 6fb6d1cf90.
* Revert "[CSOptimizer] Rank disjunctions based on score only if both sides are supported"
This reverts commit 8818d399f9.
* Revert "[CSOptimizer] Rank results of operators regardless of whether anything is known about parameters"
This reverts commit 3996b25fbd.
* Revert "[Tests] NFC: Add more test-cases that were previously solved due to old hacks behavior"
This reverts commit d0ff6c81b8.
* Revert "[CSOptimizer] Average score should reflect number of defaulted parameters"
This reverts commit 23589add74.
* Revert "[Tests] NFC: Adjust a couple of improved tests"
This reverts commit 66981364fe.
* Revert "[CSOptimizer] Don't optimize (implicit) calls with code completion arguments"
This reverts commit 8a918e2369.
* Revert "[CSOptimizer] attempt to rank only standard/simd operators and fully concrete overload sets"
This reverts commit deca9b61c5.
* Revert "[CSOptimizer] Record best scores for each disjunction and use them in `selectDisjunction`"
This reverts commit 3819ddfb40.
* Revert "[CSOptimizer] Let `determineBestChoicesInContext` return the best disjunction if one is available"
This reverts commit cf05405eae.
* Revert "[CSOptimizer] Emulate old behavior related to favoring of unary calls to members"
This reverts commit 527de22bec.
* Revert "[Tests] NFC: Add a test-case for rdar://133340307 which is now fast"
This reverts commit 670127abd6.
* Revert "[CSOptimizer] Prefer homogeneous arithmetic operator overloads when argument(s) or result match"
This reverts commit d69b6a0594.
* Revert "[CSOptimizer] Remove an outdated optimization to compare resolved argument types with all else equal"
This reverts commit 1760bd1f1e.
* Revert "[CSOptimizer] NFC: Switch from llvm::Optional to std::optional post-rebase"
This reverts commit c429f5b9ec.
* Revert "[CSOptimizer] Increase score when type matches opaque type"
This reverts commit 2869dff995.
* Revert "[CSOptimizer] NFC: Switch to llvm::Optional"
This reverts commit 0fc6806922.
* Revert "[CSOptimizer] NFC: Adjust conformance check to use `ConstraintSystem::lookupConformance`"
This reverts commit da65333d41.
* Revert "[CSOptimizer] Treat all type parameters equally"
This reverts commit 957a5f4270.
* Revert "[CSStep] Remove disjunction pruning logic from DisjunctionStep"
This reverts commit 2c44e37948.
* Revert "[CSOptimizer] Relax candidate type requirements from equality to set of no-impact conversions"
This reverts commit 11b897b32f.
* Revert "[CSOptimizer] Use `matchCallArguments` to establish argument-to-parameter relationships"
This reverts commit cb1cb2018d.
* Revert "[CSOptimizer] Don't attempt to optimize calls with code completion token(s) in argument position"
This reverts commit 14e2a16fce.
* Revert "[CSOptimizer] Allow generic operator overloads without associated type parameters"
This reverts commit bc5f70a9a3.
* Revert "[CSOptimizer] Make sure that all parameters without arguments are defaulted"
This reverts commit 7c1c46d4e4.
* Revert "[CSStep] Don't favor choices until the disjunction is picked"
This reverts commit e404ed722a.
* Revert "[CSOptimizer] Keep track of mismatches while evaluating candidates"
This reverts commit a094c3ebb0.
* Revert "[CSOptimizer] Favor SIMD related arithmetic operator choices if argument is SIMD<N> type"
This reverts commit c2f7451c7b.
* Revert "[CSOptimizer] Initial implementation of disjunction choice favoring algorithm"
This reverts commit 672ae3d252.
* Revert "[ConstraintSystem] Add skeleton of constraint optimizer"
This reverts commit b5f08a4009.
* Revert "[CSGen] Remove ConstraintOptimizer and all favoring logic"
This reverts commit 4432c51f57.
* Revert "[ConstraintSystem] Remove `shrink`"
This reverts commit 757ca24e8a.
* [TypeChecker] NFC: Remove resurrected use of `SolverShrinkUnsolvedThreshold`
* [TypeChecker] Bring back `SolverDisableShrink`
* [Tests] NFC: Mark tests affected by solver-perf revert as slow
* [Tests] NFC: Adjust async tests that are affected by performance hacks
When the BitwiseCopyable experimental feature is enabled, infer types to
conform to `_BitwiseCopyable`. The `_BitwiseCopyable` inference broadly
follows the approach taken to infer `Sendable`.
(1) Special types are conformed:
- function types if trivial
- metatypes
- builtin types if trivial
(2) TheTupleType is conditionally conformed.
(3) Nominal types are conformed if:
- non-public or public+fixed-layout
- enum or struct (non-class)
- every field conforms to _BitwiseCopyable
Additionally, check that nominal types which are explicitly conformed to
`_BitwiseCopyable` satisfy the latter two conditions of (3).
For a public, non-fixed-layout type to conform to `_BitwiseCopyable`,
the user must conform the type explicitly.
Finally, verify that conformances correspond to TypeLowering's notion of
triviality to the appropriate extent:
- if a type isn't trivial, it doesn't conform to `_BitwiseCopyable`
unless it's an archetype
- if a type is trivial, it conforms to `_BitwiseCopyable` unless some
field in its layout doesn't conform to `_BitwiseCopyable`, which is
only permitted under certain circumstances (the type has generic
parameters, the type is public non-fixed-layout, the type is a
reference but has ReferenceStorage::Unmanaged, the type is a
ModuleType, etc.)
This implementation has the function execute a request to scan the
inheritance clause of non-protocol nominals for a `~Copyable`. For
protocols, we look in the requirement signature.
This isn't our final state, as the GenericEnvironment needs to be
queried in general to determine of a Type is noncopyable. So for now
checking for a `~Copyable` only makes sense for Decls.
Use FetchContent to include swift-syntax directly in swift. This can be
thought of as an `add_subdirectory` for a directory outside the root.
The default build directory will be `_deps/swiftsyntax-subbuild/`, though
the modules and shared libraries will be built in `lib/swift/host` by
passing down `SWIFT_HOST_LIBRARIES_DEST_DIR` to avoid copying them as we
were doing previously.
As of CMake 3.25, there are now global variables `LINUX=1`, `ANDROID=1`,
etc. These conflict with expressions that used these names as unquoted
strings in positions where CMake accepts 'variable|string', for example:
- `if(sdk STREQUAL LINUX)` would fail, because `LINUX` is now defined and
expands to 1, where it would previously coerce to a string.
- `if(${sdk} STREQUAL "LINUX")` would fail if `sdk=LINUX`, because the
left-hand side expands twice.
In this patch, I looked for a number of patterns to fix up, sometimes a
little defensively:
- Quoted right-hand side of `STREQUAL` where I was confident it was
intended to be a string literal.
- Removed manual variable expansion on left-hand side of `STREQUAL`,
`MATCHES` and `IN_LIST` where I was confident it was unintended.
Fixes#65028.
For future usage from other host libraries written in Swift
For CMake:
* Explicitly specify LINKER_LANGAGE to CXX in existing components so
that 'swiftc' is not used when linking with 'swiftASTGen'
* Add 'EMIT_MODULE' argument to 'add_pure_swift_host_library' to emit
.swiftmodule usable from other Swift libraries.
Executable compiler plugins are programs invoked by the host compiler
and communicate with the host with IPC via standard IO (stdin/stdout.)
Each message is serialized in JSON, prefixed with a header which is a
64bit little-endian integer indicating the size of the message.
* Basic/ExecuteWithPipe: External program invocation. Lik
llvm::sys::ExecuteNoWait() but establishing pipes to the child's
stdin/stdout
* Basic/Sandbox: Sandboxed execution helper. Create command line
arguments to be executed in sandbox environment (similar to SwiftPM's
pluging sandbox)
* AST/PluginRepository: ASTContext independent plugin manager
* ASTGen/PluginHost: Communication with the plugin. Messages are
serialized by ASTGen/LLVMJSON
rdar://101508815
Introduce an experimental option `BuiltinMacros` that takes the magic
literals (`#file`, `#line`, `#function`, etc.) after type checking and
processes the original source for the expression using the build
syntactic macro system in the swift-syntax library. At present, the
result of expansion is printed to standard output, but it's enough to
verify that we're able to find the corresponding syntax node based on
the C++ AST.
When parsing a regular expression literal, accept a serialized capture structure from the regex parser. During type checking, decode it and form Swift types.
Examples:
```swift
'/(.)(.)/' // ==> `Regex<(Substring, Substring)>`
'/(?<label>.)(.)/' // ==> `Regex<(label: Substring, Substring)`
'/((.))*((.)?)/' //==> `Regex<([Substring], [Substring], Substring, Substring?)>`
```
Also:
- Fix a bug where a regex literal parsing error is not returning an error parser result.
Note:
- This needs to land after apple/swift-experimental-string-processing#92 and after `dev/4` tag has been created.
- See apple/swift-experimental-string-processing#92 for regex parser changes and the capture structure encoding.
- The `RegexLiteralParsingFn` `CaptureStructureOut` pointer type change from `char *` to `void *` will not break builds due to implicit pointer conversion (SE-0324) and unchanged ABI.
Resolves rdar://83253511.
* [Distributed] Initial distributed checking
* [Distributed] initial types shapes and conform to DistributedActor
* [Distributed] Require Codable params and return types
* [Distributed] initial synthesis of fields and constructors
* [Distributed] Field and initializer synthesis
* [Distributed] Codable requirement on distributed funcs; also handle <T: Codable>
* [Distributed] handle generic type params which are Codable in dist func
[Distributed] conformsToProtocol after all
* [Distributed] Implement remote flag on actors
* Implement remote flag on actors
* add test
* actor initializer that sets remote flag
[Distributed] conformances getting there
* [Distributed] dont require async throws; cleanup compile tests
* [Distributed] do not synthesize default implicit init, only our special ones
* [Distributed] properly synth inits and properties; mark actorTransport as _distributedActorIndependent
Also:
- do not synthesize default init() initializer for dist actor
* [Distributed] init(transport:) designated and typechecking
* [Distributed] dist actor initializers MUST delegate to local-init
* [Distributed] check if any ctors in delegation call init(transport:)
* [Distributed] check init(transport:) delegation through many inits; ban invoking init(resolve:using:) explicitly
* [Distributed] disable IRGen test for now
* [Distributed] Rebase cleanups
* [Concurrent] transport and address are concurrent value
* [Distributed] introduce -enable-experimental-distributed flag
* rebase adjustments again
* rebase again...
* [Distributed] distributed functions are implicitly async+throws outside the actor
* [Distributed] implicitly throwing and async distributed funcs
* remove printlns
* add more checks to implicit function test
* [Distributed] resolve initializer now marks the isRemote actor flag
* [Distributed] distributedActor_destroy invoked instead, rather than before normal
* [Distributed] Generate distributed thunk for actors
* [distributed] typechecking for _remote_ functions existing, add tests for remote funcs
* adding one XFAIL'ed task & actor lifetime test
The `executor_deinit1` test fails 100% of the time
(from what I've seen) so I thought we could track
and see when/if someone happens to fix this bug.
Also, added extra coverage for #36298 via `executor_deinit2`
* Fix a memory issue with actors in the runtime system, by @phausler
* add new test that now passes because of patch by @phausler
See previous commit in this PR.
Test is based on one from rdar://74281361
* fix all tests that require the _remote_ function stubs
* Do not infer @actorIndependent onto `let` decls
* REVERT_ME: remove some tests that hacky workarounds will fail
* another flaky test, help build toolchain
* [Distributed] experimental distributed implies experimental concurrency
* [Distributed] Allow distributed function that are not marked async or throws
* [Distributed] make attrs SIMPLE to get serialization generated
* [Distributed] ActorAddress must be Hashable
* [Distributed] Implement transport.actorReady call in local init
* cleanup after rebase
* [Distributed] add availability attributes to all distributed actor code
* cleanup - this fixed some things
* fixing up
* fixing up
* [Distributed] introduce new Distributed module
* [Distributed] diagnose when missing 'import _Distributed'
* [Distributed] make all tests import the module
* more docs on address
* [Distributed] fixup merge issues
* cleanup: remove unnecessary code for now SIMPLE attribute
* fix: fix getActorIsolationOfContext
* [Distributed] cmake: depend on _concurrency module
* fixing tests...
* Revert "another flaky test, help build toolchain"
This reverts commit 83ae6654dd.
* remove xfail
* clenup some IR and SIL tests
* cleanup
* [Distributed] fix cmake test and ScanDependencies/can_import_with_map.swift
* [Distributed] fix flags/build tests
* cleanup: use isDistributed wherever possible
* [Distributed] don't import Dispatch in tests
* dont link distributed in stdlib unittest
* trying always append distributed module
* cleanups
* [Distributed] move all tests to Distributed/ directory
* [lit] try to fix lit test discovery
* [Distributed] update tests after diagnostics for implicit async changed
* [Distributed] Disable remote func tests on Windows for now
* Review cleanups
* [Distributed] fix typo, fixes Concurrency/actor_isolation_objc.swift
* [Distributed] attributes are DistributedOnly (only)
* cleanup
* [Distributed] cleanup: rely on DistributedOnly for guarding the keyword
* Update include/swift/AST/ActorIsolation.h
Co-authored-by: Doug Gregor <dgregor@apple.com>
* introduce isAnyThunk, minor cleanup
* wip
* [Distributed] move some type checking to TypeCheckDistributed.cpp
* [TypeCheckAttr] remove extra debug info
* [Distributed/AutoDiff] fix SILDeclRef creation which caused AutoDiff issue
* cleanups
* [lit] remove json import from lit test suite, not needed after all
* [Distributed] distributed functions only in DistributedActor protocols
* [Distributed] fix flag overlap & build setting
* [Distributed] Simplify noteIsolatedActorMember to not take bool distributed param
* [Distributed] make __isRemote not public
* [Distributed] Fix availability and remove actor class tests
* [actorIndependent] do not apply actorIndependent implicitly to values where it would be illegal to apply
* [Distributed] disable tests until issue fixed
Co-authored-by: Dario Rexin <drexin@apple.com>
Co-authored-by: Kavon Farvardin <kfarvardin@apple.com>
Co-authored-by: Doug Gregor <dgregor@apple.com>
* Revert "[Distributed] disable tests until issue fixed"
This reverts commit 0a04278920.
* Revert "[Distributed] Initial `distributed` actors and functions and new module (#37109)"
This reverts commit 814ede0cf3.
* [Distributed] Initial distributed checking
* [Distributed] initial types shapes and conform to DistributedActor
* [Distributed] Require Codable params and return types
* [Distributed] initial synthesis of fields and constructors
* [Distributed] Field and initializer synthesis
* [Distributed] Codable requirement on distributed funcs; also handle <T: Codable>
* [Distributed] handle generic type params which are Codable in dist func
[Distributed] conformsToProtocol after all
* [Distributed] Implement remote flag on actors
* Implement remote flag on actors
* add test
* actor initializer that sets remote flag
[Distributed] conformances getting there
* [Distributed] dont require async throws; cleanup compile tests
* [Distributed] do not synthesize default implicit init, only our special ones
* [Distributed] properly synth inits and properties; mark actorTransport as _distributedActorIndependent
Also:
- do not synthesize default init() initializer for dist actor
* [Distributed] init(transport:) designated and typechecking
* [Distributed] dist actor initializers MUST delegate to local-init
* [Distributed] check if any ctors in delegation call init(transport:)
* [Distributed] check init(transport:) delegation through many inits; ban invoking init(resolve:using:) explicitly
* [Distributed] disable IRGen test for now
* [Distributed] Rebase cleanups
* [Concurrent] transport and address are concurrent value
* [Distributed] introduce -enable-experimental-distributed flag
* rebase adjustments again
* rebase again...
* [Distributed] distributed functions are implicitly async+throws outside the actor
* [Distributed] implicitly throwing and async distributed funcs
* remove printlns
* add more checks to implicit function test
* [Distributed] resolve initializer now marks the isRemote actor flag
* [Distributed] distributedActor_destroy invoked instead, rather than before normal
* [Distributed] Generate distributed thunk for actors
* [distributed] typechecking for _remote_ functions existing, add tests for remote funcs
* adding one XFAIL'ed task & actor lifetime test
The `executor_deinit1` test fails 100% of the time
(from what I've seen) so I thought we could track
and see when/if someone happens to fix this bug.
Also, added extra coverage for #36298 via `executor_deinit2`
* Fix a memory issue with actors in the runtime system, by @phausler
* add new test that now passes because of patch by @phausler
See previous commit in this PR.
Test is based on one from rdar://74281361
* fix all tests that require the _remote_ function stubs
* Do not infer @actorIndependent onto `let` decls
* REVERT_ME: remove some tests that hacky workarounds will fail
* another flaky test, help build toolchain
* [Distributed] experimental distributed implies experimental concurrency
* [Distributed] Allow distributed function that are not marked async or throws
* [Distributed] make attrs SIMPLE to get serialization generated
* [Distributed] ActorAddress must be Hashable
* [Distributed] Implement transport.actorReady call in local init
* cleanup after rebase
* [Distributed] add availability attributes to all distributed actor code
* cleanup - this fixed some things
* fixing up
* fixing up
* [Distributed] introduce new Distributed module
* [Distributed] diagnose when missing 'import _Distributed'
* [Distributed] make all tests import the module
* more docs on address
* [Distributed] fixup merge issues
* cleanup: remove unnecessary code for now SIMPLE attribute
* fix: fix getActorIsolationOfContext
* [Distributed] cmake: depend on _concurrency module
* fixing tests...
* Revert "another flaky test, help build toolchain"
This reverts commit 83ae6654dd.
* remove xfail
* clenup some IR and SIL tests
* cleanup
* [Distributed] fix cmake test and ScanDependencies/can_import_with_map.swift
* [Distributed] fix flags/build tests
* cleanup: use isDistributed wherever possible
* [Distributed] don't import Dispatch in tests
* dont link distributed in stdlib unittest
* trying always append distributed module
* cleanups
* [Distributed] move all tests to Distributed/ directory
* [lit] try to fix lit test discovery
* [Distributed] update tests after diagnostics for implicit async changed
* [Distributed] Disable remote func tests on Windows for now
* Review cleanups
* [Distributed] fix typo, fixes Concurrency/actor_isolation_objc.swift
* [Distributed] attributes are DistributedOnly (only)
* cleanup
* [Distributed] cleanup: rely on DistributedOnly for guarding the keyword
* Update include/swift/AST/ActorIsolation.h
Co-authored-by: Doug Gregor <dgregor@apple.com>
* introduce isAnyThunk, minor cleanup
* wip
* [Distributed] move some type checking to TypeCheckDistributed.cpp
* [TypeCheckAttr] remove extra debug info
* [Distributed/AutoDiff] fix SILDeclRef creation which caused AutoDiff issue
* cleanups
* [lit] remove json import from lit test suite, not needed after all
* [Distributed] distributed functions only in DistributedActor protocols
* [Distributed] fix flag overlap & build setting
* [Distributed] Simplify noteIsolatedActorMember to not take bool distributed param
* [Distributed] make __isRemote not public
Co-authored-by: Dario Rexin <drexin@apple.com>
Co-authored-by: Kavon Farvardin <kfarvardin@apple.com>
Co-authored-by: Doug Gregor <dgregor@apple.com>
Otherwise we set it on all targets/languages in a subdirectory (I forgot if it
propagates up). Regardless, this type of viral stuff is something we want to
move away from since it creates a code that is a "forall" piece of code rather
than a piece of code that only effects a single target.
I also conditionalized the actual definitions being added on the compiled file's
language being C,CXX,OBJC,OBJCXX since as we add Swift sources to the host side
of the compiler, we will not want these flags to propagate to Swift sources.
- Introduce an UnownedSerialExecutor type into the concurrency library.
- Create a SerialExecutor protocol which allows an executor type to
change how it executes jobs.
- Add an unownedExecutor requirement to the Actor protocol.
- Change the ABI for ExecutorRef so that it stores a SerialExecutor
witness table pointer in the implementation field. This effectively
makes ExecutorRef an `unowned(unsafe) SerialExecutor`, except that
default actors are represented without a witness table pointer (just
a bit-pattern).
- Synthesize the unownedExecutor method for default actors (i.e. actors
that don't provide an unownedExecutor property).
- Make synthesized unownedExecutor properties `final`, and give them
a semantics attribute specifying that they're for default actors.
- Split `Builtin.buildSerialExecutorRef` into a few more precise
builtins. We're not using the main-actor one yet, though.
Pitch thread:
https://forums.swift.org/t/support-custom-executors-in-swift-concurrency/44425
The backs out of some early decisions we made about actor layout
that we don't need. Custom actors will use a different approach.
This should suffice for the remainder of rdar://70146827.
Introduce a new Actor protocol, which is a class-bound protocol with only
one requirement:
func enqueue(partialTask: PartialAsyncTask)
All actor classes implicitly conform to this protocol, and will synthesize
a (currently empty) definition of `enqueue(partialTask:)` unless a suitable
one is provided explicitly.
