AST: Synthesize ExtensionDecls for conditional conformances of Builtin.TheTupleType to Sendable and Copyable

Author: slavapestov

lib/AST/ASTContext.cpp

@@ -6296,10 +6296,44 @@ BuiltinTupleDecl *ASTContext::getBuiltinTupleDecl() {
   if (result)
     return result;
 
-  result = new (*this) BuiltinTupleDecl(Id_TheTupleType,
-                                        TheBuiltinModule->getFiles()[0]);
+  auto *dc = TheBuiltinModule->getFiles()[0];
+
+  result = new (*this) BuiltinTupleDecl(Id_TheTupleType, dc);
   result->setAccess(AccessLevel::Public);
 
+  // Cook up conditional conformances to Sendable and Copyable.
+  auto buildFakeExtension = [&](ProtocolDecl *proto) {
+    auto protoTy = proto->getDeclaredInterfaceType();
+
+    // extension Builtin.TheTupleType: P { ... }
+    SmallVector<InheritedEntry, 1> inherited;
+    inherited.emplace_back(TypeLoc::withoutLoc(protoTy));
+    auto *ext = ExtensionDecl::create(*this, SourceLoc(), nullptr,
+                                      AllocateCopy(inherited),
+                                      dc, nullptr);
+
+    // <each T where repeat each T: P>
+    auto genericSig = result->getGenericSignature();
+    auto params = genericSig.getGenericParams();
+    assert(params.size() == 1);
+    Requirement req(RequirementKind::Conformance, params[0], protoTy);
+    genericSig = GenericSignature::get(params, req);
+    ext->setGenericSignature(genericSig);
+
+    // Bind the extension.
+    evaluator.cacheOutput(ExtendedTypeRequest{ext},
+                          result->getDeclaredInterfaceType());
+    ext->setExtendedNominal(result);
+
+    result->addExtension(ext);
+  };
+
+  if (auto *proto = getProtocol(KnownProtocolKind::Sendable))
+    buildFakeExtension(proto);
+
+  if (auto *proto = getProtocol(KnownProtocolKind::Copyable))
+    buildFakeExtension(proto);
+
   return result;
 }