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Our standard conception of suppressible features assumes we should always suppress the feature if the compiler doesn't support it. This presumes that there's no harm in suppressing the feature, and that's a fine assumption for features that are just adding information or suppressing new diagnostics. Features that are semantically relevant, maybe even ABI-breaking, are not a good fit for this, and so instead of reprinting the decl with the feature suppressed, we just have to hide the decl entirely. The missing middle here is that it's sometimes useful to be able to adopt a type change to an existing declaration, and we'd like older compilers to be able to use the older version of the declaration. Making a type change this way is, of course, only really acceptable for @_alwaysEmitIntoClient declarations; but those represent quite a few declarations that we'd like to be able to refine the types of. Rather than trying to come up with heuristics based on @_alwaysEmitIntoClient or other sources of information, this design just requires the declaration to opt in with a new attribute, @_allowFeatureSuppress. When a declaration opts in to suppression for a conditionally-suppressible feature, the printer uses the suppression serially-print-with-downgraded-options approach; otherwise it uses the print-only-if-feature-is-available approach.
71 lines
2.3 KiB
C++
71 lines
2.3 KiB
C++
//===--- Feature.h - Helpers related to Swift features ----------*- C++ -*-===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See https://swift.org/LICENSE.txt for license information
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// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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#ifndef SWIFT_BASIC_FEATURES_H
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#define SWIFT_BASIC_FEATURES_H
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#include "llvm/ADT/StringRef.h"
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#include <optional>
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namespace swift {
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class LangOptions;
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/// Enumeration describing all of the named features.
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enum class Feature {
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#define LANGUAGE_FEATURE(FeatureName, SENumber, Description) FeatureName,
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#include "swift/Basic/Features.def"
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};
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constexpr unsigned numFeatures() {
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enum Features {
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#define LANGUAGE_FEATURE(FeatureName, SENumber, Description) FeatureName,
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#include "swift/Basic/Features.def"
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NumFeatures
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};
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return NumFeatures;
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}
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/// Check whether the given feature is available in production compilers.
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bool isFeatureAvailableInProduction(Feature feature);
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/// Determine the in-source name of the given feature.
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llvm::StringRef getFeatureName(Feature feature);
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/// Determine whether the first feature is more recent (and thus implies
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/// the existence of) the second feature. Only meaningful for suppressible
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/// features.
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inline bool featureImpliesFeature(Feature feature, Feature implied) {
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// Suppressible features are expected to be listed in order of
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// addition in Features.def.
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return (unsigned) feature < (unsigned) implied;
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}
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/// Get the feature corresponding to this "future" feature, if there is one.
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std::optional<Feature> getUpcomingFeature(llvm::StringRef name);
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/// Get the feature corresponding to this "experimental" feature, if there is
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/// one.
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std::optional<Feature> getExperimentalFeature(llvm::StringRef name);
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/// Get the major language version in which this feature was introduced, or
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/// \c None if it does not have such a version.
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std::optional<unsigned> getFeatureLanguageVersion(Feature feature);
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/// Determine whether this feature should be included in the
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/// module interface
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bool includeInModuleInterface(Feature feature);
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}
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#endif // SWIFT_BASIC_FEATURES_H
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