AST: ModuleDecl::lookupConformance() looks for conformances on Builtin.TheTupleType given a tuple type

Author: slavapestov

lib/AST/Module.cpp

@@ -1137,9 +1137,45 @@ ProtocolConformanceRef ModuleDecl::lookupConformance(Type type,
 static ProtocolConformanceRef getBuiltinTupleTypeConformance(
     Type type, const TupleType *tupleType, ProtocolDecl *protocol,
     ModuleDecl *module) {
+  ASTContext &ctx = protocol->getASTContext();
+
+  // This is the new code path.
+  //
+  // FIXME: Remove the Sendable stuff below.
+  auto *tupleDecl = ctx.getBuiltinTupleDecl();
+
+  // Find the (unspecialized) conformance.
+  SmallVector<ProtocolConformance *, 2> conformances;
+  if (tupleDecl->lookupConformance(protocol, conformances)) {
+    // If we have multiple conformances, first try to filter out any that are
+    // unavailable on the current deployment target.
+    //
+    // FIXME: Conformance lookup should really depend on source location for
+    // this to be 100% correct.
+    if (conformances.size() > 1) {
+      SmallVector<ProtocolConformance *, 2> availableConformances;
+
+      for (auto *conformance : conformances) {
+        if (conformance->getDeclContext()->isAlwaysAvailableConformanceContext())
+          availableConformances.push_back(conformance);
+      }
+
+      // Don't filter anything out if all conformances are unavailable.
+      if (!availableConformances.empty())
+        std::swap(availableConformances, conformances);
+    }
+
+    auto *conformance = cast<NormalProtocolConformance>(conformances.front());
+    auto subMap = type->getContextSubstitutionMap(module,
+                                                  conformance->getDeclContext());
+
+    // TODO: labels
+    auto *specialized = ctx.getSpecializedConformance(type, conformance, subMap);
+    return ProtocolConformanceRef(specialized);
+  }
+
   // Tuple type are Sendable when all of their element types are Sendable.
   if (protocol->isSpecificProtocol(KnownProtocolKind::Sendable)) {
-    ASTContext &ctx = protocol->getASTContext();
 
     // Create the pieces for a generic tuple type (T1, T2, ... TN) and a
     // generic signature <T1, T2, ..., TN>.