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[NFC] Implement a small DSL to create metadata objects in unit tests
Some parts of the type metadata system are difficult to unit-test because they rely on structures that contain relative references, which the C compiler cannot generate. We have traditionally just relied on integration testing with the compiler. For constrained existentials, I wanted to do better, so I spent a few days hacking up this little system which can generate graphs of objects with relative references to one another. Currently it's missing the ability to generate a lot of things which I didn't need in order to adequately test the metadata system for constrained existentials.
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‎unittests/runtime/MetadataObjectBuilder.h

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//===--- MetadataObjectBuilder.h -------------------------------*- 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 - 2022 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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//
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// Defines routines for use with ObjectBuilder that are specifically
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// useful for building metadata objects.
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//
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//===----------------------------------------------------------------------===//
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#ifndef METADATA_OBJECT_BUILDER_H
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#define METADATA_OBJECT_BUILDER_H
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#include "ObjectBuilder.h"
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#include "SpecifierDSL.h"
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#include "swift/ABI/Metadata.h"
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#include <sstream>
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#include <type_traits>
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namespace swift {
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using namespace specifierDSL;
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/// Add a simple ModuleContextDescriptor with the given name.
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inline void addModuleContextDescriptor(AnyObjectBuilder &builder,
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StringRef moduleName) {
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// Context descriptor flags
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auto contextFlags = ContextDescriptorFlags(ContextDescriptorKind::Module,
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/*generic*/ false,
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/*unique*/ true,
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/*version*/ 0,
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/*kindSpecific*/ 0);
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builder.add32(contextFlags.getIntValue());
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// Parent
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builder.add32(0);
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// Name
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builder.addRelativeReferenceToString(moduleName);
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}
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/// Add a simple ProtocolDescriptor with the given base protocols
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/// but no other requirements.
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inline void addProtocolDescriptor(AnyObjectBuilder &builder,
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const ModuleContextDescriptor *module,
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StringRef protocolName,
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llvm::ArrayRef<ProtocolSpecifier> baseProtocols) {
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// Context descriptor flags
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auto contextFlags = ContextDescriptorFlags(ContextDescriptorKind::Protocol,
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/*generic*/ false,
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/*unique*/ true,
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/*version*/ 0,
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/*kindSpecific*/ 0);
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builder.add32(contextFlags.getIntValue());
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// Parent
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builder.addRelativeIndirectReference(module, /*addend*/ 1);
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// Name
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builder.addRelativeReferenceToString(protocolName);
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// NumRequirementsInSignature
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builder.add32(baseProtocols.size());
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// NumRequirements
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builder.add32(baseProtocols.size());
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// Associated type names
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builder.add32(0);
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ObjectRef<const char> selfType;
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if (!baseProtocols.empty()) {
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auto subbuilder = builder.createSubobject<const char>(/*align*/ 2);
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mangleGenericParamType(subbuilder, 0, 0);
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selfType = subbuilder.ref();
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}
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// Requirement signature requirement descriptors
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for (auto &baseProtocol : baseProtocols) {
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addConformanceRequirement(builder, selfType, baseProtocol);
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}
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// Protocol requirement descriptors
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for (auto baseProtocol : baseProtocols) {
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(void) baseProtocol; // Requirements don't actually collect specifics here
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// Flags
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auto flags = ProtocolRequirementFlags(
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ProtocolRequirementFlags::Kind::BaseProtocol);
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builder.add32(flags.getIntValue());
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// Default implementation
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builder.add32(0);
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}
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}
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template <class T>
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class GlobalObjectBuilder {
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ObjectBuilder<T> builder;
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public:
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template <class Fn>
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GlobalObjectBuilder(Fn &&fn) {
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std::forward<Fn>(fn)(builder);
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(void) builder.finish();
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}
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const T *get() const { return builder.get(); }
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};
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/// Build a global object with the given lambda.
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///
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/// This uses a static local to magically cache and preserve the
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/// global object. This global caching is uniqued by the template
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/// arguments to this function, so callers should not re-use lambdas
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/// for different calls.
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template <class T, class Fn>
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inline const T *buildGlobalObject(Fn &&fn) {
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static const GlobalObjectBuilder<T> builder(std::forward<Fn>(fn));
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return builder.get();
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}
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/// Build a global ModuleContextDescriptor with the name returned by the
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/// given lambda.
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///
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/// This uses a static local to magically cache and preserve the
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/// global object. This global caching is uniqued by the template
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/// arguments to this function, so callers should not re-use lambdas
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/// for different calls.
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template <class Fn>
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inline const ModuleContextDescriptor *
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buildGlobalModuleContextDescriptor(Fn &&fn) {
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static const GlobalObjectBuilder<ModuleContextDescriptor> builder(
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[&](AnyObjectBuilder &builder) {
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addModuleContextDescriptor(builder, std::forward<Fn>(fn)());
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});
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return builder.get();
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}
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/// Build a global protocol descriptor for an empty protocol with
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/// the name returned by the given lambda.
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///
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/// This uses a static local to magically cache and preserve the
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/// global object. This global caching is uniqued by the template
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/// arguments to this function, so callers should not re-use lambdas
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/// for different calls.
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template <class Fn>
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inline const ProtocolDescriptor *
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buildGlobalProtocolDescriptor(const ModuleContextDescriptor *module, Fn &&fn) {
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static const GlobalObjectBuilder<ProtocolDescriptor> builder(
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[&](AnyObjectBuilder &builder) {
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addProtocolDescriptor(builder, module, std::forward<Fn>(fn)(), {});
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});
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return builder.get();
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}
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} // end namespace swift
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#endif

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