Merge pull request #78153 from artemcm/ResolveImplicitConformancesDeserialization

[Deserialization] Use `swift::lookupConformance` to resolve implicit conformances

Author: artemcm

lib/Serialization/Deserialization.cpp

@@ -18,6 +18,7 @@
 #include "swift/AST/Attr.h"
 #include "swift/AST/AttrKind.h"
 #include "swift/AST/AutoDiff.h"
+#include "swift/AST/ConformanceLookup.h"
 #include "swift/AST/DiagnosticsSema.h"
 #include "swift/AST/DistributedDecl.h"
 #include "swift/AST/Expr.h"
@@ -957,16 +958,29 @@ ProtocolConformanceDeserializer::readNormalProtocolConformanceXRef(
   if (!module)
     module = MF.getAssociatedModule();
 
-  SmallVector<ProtocolConformance *, 2> conformances;
-  nominal->lookupConformance(proto, conformances);
   PrettyStackTraceModuleFile traceMsg(
       "If you're seeing a crash here, check that your SDK and dependencies "
       "are at least as new as the versions used to build", MF);
-  // This would normally be an assertion but it's more useful to print the
-  // PrettyStackTrace here even in no-asserts builds.
-  if (conformances.empty())
-    abort();
-  return conformances.front();
+
+  // Because Sendable conformances are currently inferred with
+  // 'ImplicitKnownProtocolConformanceRequest' in swift::lookupConformance,
+  // we may end up in a situation where we are deserializing such inferred
+  // conformance but a lookup on the 'NominalDecl' will not succeed nor
+  // will it run inference logic. For now, special-case 'Sendable' lookups
+  // here.
+  // TODO: Sink Sendable derivation into the conformance lookup table
+  if (proto->isSpecificProtocol(KnownProtocolKind::Sendable)) {
+    auto conformanceRef = lookupConformance(nominal->getDeclaredInterfaceType(), proto);
+    if (!conformanceRef.isConcrete())
+      abort();
+    return conformanceRef.getConcrete();
+  } else {
+    SmallVector<ProtocolConformance *, 2> conformances;
+    nominal->lookupConformance(proto, conformances);
+    if (conformances.empty())
+      abort();
+    return conformances.front();
+  }
 }
 
 Expected<ProtocolConformance *>