[Module interface] Use features in module interface generation. #35839
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When generating a module interface, emit `#if` around any declarations that are tied to specific, named language features. This allows module interfaces to be processed by older Swift compilers that do not support these newer features, such as async/await or actors. The amount of effort required to correctly handle a new kind of feature varies somewhat drastically based on the feature itself. The "simple" case is where a particular declaration can only exist if a feature is available. For example, and `async` declaration is fairly easy to handle; a `@_marker` protocol's conformances are not. Fixes rdar://73326633.
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@swift-ci please smoke test |
lib/AST/ASTPrinter.cpp
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| static bool usesFeatureAsyncAwait(Decl *decl) { | ||
| if (auto func = dyn_cast<AbstractFunctionDecl>(decl)) { | ||
| if (func->hasAsync()) | ||
| return true; | ||
| } | ||
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| return false; | ||
| } | ||
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| static bool usesFeatureMarkerProtocol(Decl *decl) { | ||
| if (auto proto = dyn_cast<ProtocolDecl>(decl)) { | ||
| if (proto->isMarkerProtocol()) | ||
| return true; | ||
| } | ||
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| if (auto ext = dyn_cast<ExtensionDecl>(decl)) { | ||
| for (const auto &req: ext->getGenericRequirements()) { | ||
| if (req.getKind() == RequirementKind::Conformance && | ||
| req.getSecondType()->castTo<ProtocolType>()->getDecl() | ||
| ->isMarkerProtocol()) | ||
| return true; | ||
| } | ||
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| for (const auto &inherited : ext->getInherited()) { | ||
| if (auto inheritedType = inherited.getType()) { | ||
| if (inheritedType->isExistentialType()) { | ||
| auto layout = inheritedType->getExistentialLayout(); | ||
| for (ProtocolType *protoTy : layout.getProtocols()) { | ||
| if (protoTy->getDecl()->isMarkerProtocol()) | ||
| return true; | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| return false; | ||
| } | ||
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| static bool usesFeatureActors(Decl *decl) { | ||
| if (auto classDecl = dyn_cast<ClassDecl>(decl)) { | ||
| if (classDecl->isActor()) | ||
| return true; | ||
| } | ||
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| if (auto ext = dyn_cast<ExtensionDecl>(decl)) { | ||
| if (auto classDecl = ext->getSelfClassDecl()) | ||
| if (classDecl->isActor()) | ||
| return true; | ||
| } | ||
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| return false; | ||
| } |
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Unless I'm mistaken, all three of these probably ought to walk into any parameter or result types and look for the feature being used there, too. For instance, if you write:
public func runAsync(_ fn: () async -> Void) { ... }
That probably ought to be guarded by #if $AsyncAwait, even though runAsync(_:) itself isn't an async function. Similarly:
public func transact(with account: BankAccount)
Probably ought to be guarded by #if $Actors if BankAccount is an actor class, even though transact(with:) isn't itself an actor class.
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I went ahead and did a bunch of this checking. It is not comprehensive, I'm sure, although we could probably do some additional meta programming to make it less boilerplate-y and more comprehensive.
lib/AST/ASTPrinter.cpp
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| static std::vector<Feature> getFeaturesUsed(Decl *decl) { | ||
| std::vector<Feature> features; | ||
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| // Only type- and module-scope declarations have any features to speak of. |
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Note that, by my expanded definition of "having a feature", this comment is no longer true.
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Right, I've zapped this. Thanks!
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@swift-ci please smoke test |
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@swift-ci please smoke test Linux |
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Hi @DougGregor – The test is broken and confusing. Superficially, it needs Also, FYI: |
When generating a module interface, emit
#ifaround any declarationsthat are tied to specific, named language features. This allows module
interfaces to be processed by older Swift compilers that do not
support these newer features, such as async/await or actors.
The amount of effort required to correctly handle a new kind of
feature varies somewhat drastically based on the feature itself. The
"simple" case is where a particular declaration can only exist if a
feature is available. For example, and
asyncdeclaration is fairlyeasy to handle; a
@_markerprotocol's conformances are not.Fixes rdar://73326633.
Design credit to @beccadax, bugs are my own.