AST: Allow ModuleDecl::lookupConformance() to construct PackConformances for PackTypes

lib/AST/Module.cpp

@@ -32,6 +32,7 @@
 #include "swift/AST/ModuleLoader.h"
 #include "swift/AST/NameLookup.h"
 #include "swift/AST/NameLookupRequests.h"
+#include "swift/AST/PackConformance.h"
 #include "swift/AST/ParseRequests.h"
 #include "swift/AST/PrettyStackTrace.h"
 #include "swift/AST/PrintOptions.h"
@@ -1259,6 +1260,33 @@ static ProtocolConformanceRef getBuiltinBuiltinTypeConformance(
   return ProtocolConformanceRef::forMissingOrInvalid(type, protocol);
 }
 
+static ProtocolConformanceRef getPackTypeConformance(
+    PackType *type, ProtocolDecl *protocol, ModuleDecl *mod) {
+  SmallVector<ProtocolConformanceRef, 2> patternConformances;
+
+  for (auto packElement : type->getElementTypes()) {
+    if (auto *packExpansion = packElement->getAs<PackExpansionType>()) {
+      auto patternType = packExpansion->getPatternType();
+
+      auto patternConformance =
+          (patternType->isTypeParameter()
+           ? ProtocolConformanceRef(protocol)
+           : mod->lookupConformance(patternType, protocol));
+      patternConformances.push_back(patternConformance);
+      continue;
+    }
+
+    auto patternConformance =
+        (packElement->isTypeParameter()
+         ? ProtocolConformanceRef(protocol)
+         : mod->lookupConformance(packElement, protocol));
+    patternConformances.push_back(patternConformance);
+  }
+
+  return ProtocolConformanceRef(
+      PackConformance::get(type, protocol, patternConformances));
+}
+
 ProtocolConformanceRef
 LookupConformanceInModuleRequest::evaluate(
     Evaluator &evaluator, LookupConformanceDescriptor desc) const {
@@ -1322,6 +1350,11 @@ LookupConformanceInModuleRequest::evaluate(
   if (type->is<UnresolvedType>() || type->is<PlaceholderType>())
     return ProtocolConformanceRef(protocol);
 
+  // Pack types can conform to protocols.
+  if (auto packType = type->getAs<PackType>()) {
+    return getPackTypeConformance(packType, protocol, mod);
+  }
+
   // Tuple types can conform to protocols.
   if (auto tupleType = type->getAs<TupleType>()) {
     return getBuiltinTupleTypeConformance(type, tupleType, protocol, mod);