[Sema] Pass down ProtocolConformance to DerivedConformance

Previously `getHashableConformance` was attempting
to find the conformance itself, which could fail
(rdar://129620291). Instead, pass down the
known protocol conformance that we're deriving
a witness for. No test case unfortunately as I
haven't been able to come up with a reproducer.

rdar://129620291

Author: hamishknight

lib/Sema/AssociatedTypeInference.cpp

@@ -2489,20 +2489,16 @@ AssociatedTypeInference::computeDefaultTypeWitness(
 }
 
 static std::pair<Type, TypeDecl *>
-deriveTypeWitness(DeclContext *DC,
-                  NominalTypeDecl *TypeDecl,
-                  AssociatedTypeDecl *AssocType) {
+deriveTypeWitness(const NormalProtocolConformance *Conformance,
+                  NominalTypeDecl *TypeDecl, AssociatedTypeDecl *AssocType) {
   auto *protocol = cast<ProtocolDecl>(AssocType->getDeclContext());
 
   auto knownKind = protocol->getKnownProtocolKind();
 
   if (!knownKind)
     return std::make_pair(nullptr, nullptr);
 
-  auto Decl = DC->getInnermostDeclarationDeclContext();
-
-  DerivedConformance derived(TypeDecl->getASTContext(), Decl, TypeDecl,
-                             protocol);
+  DerivedConformance derived(Conformance, TypeDecl, protocol);
   switch (*knownKind) {
   case KnownProtocolKind::RawRepresentable:
     return std::make_pair(derived.deriveRawRepresentable(AssocType), nullptr);
@@ -2536,7 +2532,7 @@ AssociatedTypeInference::computeDerivedTypeWitness(
     return std::make_pair(Type(), nullptr);
 
   // Try to derive the type witness.
-  auto result = deriveTypeWitness(dc, derivingTypeDecl, assocType);
+  auto result = deriveTypeWitness(conformance, derivingTypeDecl, assocType);
   if (!result.first)
     return std::make_pair(Type(), nullptr);
 

lib/Sema/DerivedConformanceEquatableHashable.cpp

@@ -953,20 +953,6 @@ getHashValueRequirement(ASTContext &C) {
   return nullptr;
 }
 
-static ProtocolConformance *
-getHashableConformance(const Decl *parentDecl) {
-  ASTContext &C = parentDecl->getASTContext();
-  const auto IDC = cast<IterableDeclContext>(parentDecl);
-  auto hashableProto = C.getProtocol(KnownProtocolKind::Hashable);
-  for (auto conformance: IDC->getLocalConformances(
-           ConformanceLookupKind::NonStructural)) {
-    if (conformance->getProtocol() == hashableProto) {
-      return conformance;
-    }
-  }
-  return nullptr;
-}
-
 bool DerivedConformance::canDeriveHashable(NominalTypeDecl *type) {
   // FIXME: This is not actually correct. We cannot promise to always
   // provide a witness here in all cases. Unfortunately, figuring out
@@ -996,8 +982,7 @@ ValueDecl *DerivedConformance::deriveHashable(ValueDecl *requirement) {
   if (requirement->getBaseName() == Context.Id_hash) {
     // Start by resolving hashValue conformance.
     auto hashValueReq = getHashValueRequirement(Context);
-    auto conformance = getHashableConformance(ConformanceDecl);
-    auto hashValueDecl = conformance->getWitnessDecl(hashValueReq);
+    auto hashValueDecl = Conformance->getWitnessDecl(hashValueReq);
     if (!hashValueDecl) {
       // We won't derive hash(into:) if hashValue cannot be resolved.
       // The hashValue failure will produce a diagnostic elsewhere.

lib/Sema/DerivedConformances.cpp

@@ -29,20 +29,23 @@ using namespace swift;
 
 enum NonconformingMemberKind { AssociatedValue, StoredProperty };
 
-DerivedConformance::DerivedConformance(ASTContext &ctx, Decl *conformanceDecl,
-                                       NominalTypeDecl *nominal,
-                                       ProtocolDecl *protocol)
-    : Context(ctx), ConformanceDecl(conformanceDecl), Nominal(nominal),
-      Protocol(protocol) {
-  assert(getConformanceContext()->getSelfNominalTypeDecl() == nominal);
+DerivedConformance::DerivedConformance(
+    const NormalProtocolConformance *conformance, NominalTypeDecl *nominal,
+    ProtocolDecl *protocol)
+    : Context(nominal->getASTContext()), Conformance(conformance),
+      Nominal(nominal), Protocol(protocol) {
+  auto *DC = Conformance->getDeclContext();
+  ConformanceDecl = DC->getInnermostDeclarationDeclContext();
+  assert(ConformanceDecl);
+  assert(DC->getSelfNominalTypeDecl() == nominal);
 }
 
 DeclContext *DerivedConformance::getConformanceContext() const {
-  return cast<DeclContext>(ConformanceDecl);
+  return Conformance->getDeclContext();
 }
 
 ModuleDecl *DerivedConformance::getParentModule() const {
-  return cast<DeclContext>(ConformanceDecl)->getParentModule();
+  return getConformanceContext()->getParentModule();
 }
 
 void DerivedConformance::addMembersToConformanceContext(

lib/Sema/DerivedConformances.h

@@ -55,11 +55,12 @@ class DerivedConformance {
 
 public:
   ASTContext &Context;
+  const NormalProtocolConformance *Conformance;
   Decl *ConformanceDecl;
   NominalTypeDecl *Nominal;
   ProtocolDecl *Protocol;
 
-  DerivedConformance(ASTContext &ctx, Decl *conformanceDecl,
+  DerivedConformance(const NormalProtocolConformance *conformance,
                      NominalTypeDecl *nominal, ProtocolDecl *protocol);
 
   /// Retrieve the context in which the conformance is declared (either the

lib/Sema/TypeCheckProtocol.cpp

@@ -4500,9 +4500,9 @@ ConformanceChecker::resolveWitnessViaLookup(ValueDecl *requirement) {
   return ResolveWitnessResult::ExplicitFailed;
 }
 
-static ValueDecl *deriveProtocolRequirement(DeclContext *DC,
-                                            NominalTypeDecl *TypeDecl,
-                                            ValueDecl *Requirement) {
+static ValueDecl *
+deriveProtocolRequirement(const NormalProtocolConformance *Conformance,
+                          NominalTypeDecl *TypeDecl, ValueDecl *Requirement) {
   // Note: whenever you update this function, also update
   // DerivedConformance::getDerivableRequirement.
   const auto protocol = cast<ProtocolDecl>(Requirement->getDeclContext());
@@ -4511,12 +4511,12 @@ static ValueDecl *deriveProtocolRequirement(DeclContext *DC,
   if (!derivableKind)
     return nullptr;
 
+  auto *DC = Conformance->getDeclContext();
   const auto Decl = DC->getInnermostDeclarationDeclContext();
   if (Decl->isInvalid())
     return nullptr;
 
-  DerivedConformance derived(TypeDecl->getASTContext(), Decl, TypeDecl,
-                             protocol);
+  DerivedConformance derived(Conformance, TypeDecl, protocol);
 
   switch (*derivableKind) {
   case KnownDerivableProtocolKind::RawRepresentable:
@@ -4597,7 +4597,8 @@ ResolveWitnessResult ConformanceChecker::resolveWitnessViaDerivation(
   }
 
   // Attempt to derive the witness.
-  auto derived = deriveProtocolRequirement(DC, derivingTypeDecl, requirement);
+  auto derived =
+      deriveProtocolRequirement(Conformance, derivingTypeDecl, requirement);
 
   if (!derived) {
     return ResolveWitnessResult::ExplicitFailed;