Reflection: Add a DEBUG_TYPE_LOWERING #ifdef for diagnosing problems

To avoid crashing tools, we just propagate failure instead of
asserting. This makes debugging more difficult, though. When
this macro is enabled, messages are printed to standard error
to pinpoint the exact reason that type lowering bailed out.

Author: slavapestov

stdlib/public/Reflection/TypeLowering.cpp

@@ -24,6 +24,12 @@
 
 #include <iostream>
 
+#ifdef DEBUG_TYPE_LOWERING
+  #define DEBUG(expr) expr;
+#else
+  #define DEBUG(expr)
+#endif
+
 [[noreturn]]
 static void unreachable(const char *Message) {
   std::cerr << "fatal error: " << Message << "\n";
@@ -239,6 +245,7 @@ class ExistentialTypeInfoBuilder {
 
       const FieldDescriptor *FD = TC.getBuilder().getFieldTypeInfo(P);
       if (FD == nullptr) {
+        DEBUG(std::cerr << "No field descriptor: "; P->dump())
         Invalid = true;
         continue;
       }
@@ -275,6 +282,7 @@ class ExistentialTypeInfoBuilder {
     if (auto *P = dyn_cast<const ProtocolTypeRef>(TR)) {
       Protocols.push_back(P);
     } else {
+      DEBUG(std::cerr << "Not a protocol: "; TR->dump())
       Invalid = true;
     }
   }
@@ -286,8 +294,10 @@ class ExistentialTypeInfoBuilder {
       return nullptr;
 
     if (ObjC) {
-      if (WitnessTableCount > 0)
+      if (WitnessTableCount > 0) {
+        DEBUG(std::cerr << "@objc existential with witness tables\n");
         return nullptr;
+      }
 
       return TC.getReferenceTypeInfo(ReferenceKind::Strong,
                                      ReferenceCounting::Unknown);
@@ -316,8 +326,10 @@ class ExistentialTypeInfoBuilder {
       break;
     case ExistentialTypeRepresentation::Opaque: {
       auto *TI = TC.getTypeInfo(TC.getRawPointerTypeRef());
-      if (TI == nullptr)
+      if (TI == nullptr) {
+        DEBUG(std::cerr << "No TypeInfo for RawPointer\n");
         return nullptr;
+      }
 
       // Non-class existentials consist of a three-word buffer,
       // value metadata, and finally zero or more witness tables.
@@ -345,8 +357,10 @@ class ExistentialTypeInfoBuilder {
       return nullptr;
 
     if (ObjC) {
-      if (WitnessTableCount > 0)
+      if (WitnessTableCount > 0) {
+        DEBUG(std::cerr << "@objc existential with witness tables\n");
         return nullptr;
+      }
 
       return TC.getAnyMetatypeTypeInfo();
     }
@@ -390,6 +404,7 @@ void RecordTypeInfoBuilder::addField(const std::string &Name,
                                      const TypeRef *TR) {
   const TypeInfo *TI = TC.getTypeInfo(TR);
   if (TI == nullptr) {
+    DEBUG(std::cerr << "No TypeInfo for field type: "; TR->dump());
     Invalid = true;
     return;
   }
@@ -436,8 +451,10 @@ TypeConverter::getReferenceTypeInfo(ReferenceKind Kind,
   // Weak references do not have any extra inhabitants.
 
   auto *BuiltinTI = Builder.getBuiltinTypeInfo(TR);
-  if (BuiltinTI == nullptr)
+  if (BuiltinTI == nullptr) {
+    DEBUG(std::cerr << "No TypeInfo for reference type: "; TR->dump());
     return nullptr;
+  }
 
   unsigned numExtraInhabitants = BuiltinTI->NumExtraInhabitants;
   if (Kind == ReferenceKind::Weak)
@@ -461,8 +478,10 @@ TypeConverter::getThinFunctionTypeInfo() {
 
   auto *descriptor = getBuilder().getBuiltinTypeInfo(
       getThinFunctionTypeRef());
-  if (descriptor == nullptr)
+  if (descriptor == nullptr) {
+    DEBUG(std::cerr << "No TypeInfo for function type\n");
     return nullptr;
+  }
 
   ThinFunctionTI = makeTypeInfo<BuiltinTypeInfo>(descriptor);
 
@@ -495,8 +514,10 @@ TypeConverter::getAnyMetatypeTypeInfo() {
 
   auto *descriptor = getBuilder().getBuiltinTypeInfo(
       getAnyMetatypeTypeRef());
-  if (descriptor == nullptr)
+  if (descriptor == nullptr) {
+    DEBUG(std::cerr << "No TypeInfo for metatype type\n");
     return nullptr;
+  }
 
   AnyMetatypeTI = makeTypeInfo<BuiltinTypeInfo>(descriptor);
 
@@ -837,6 +858,7 @@ class EnumTypeInfoBuilder {
   void addCase(const std::string &Name, const TypeRef *TR,
                const TypeInfo *TI) {
     if (TI == nullptr) {
+      DEBUG(std::cerr << "No TypeInfo for case type: "; TR->dump());
       Invalid = true;
       return;
     }
@@ -967,8 +989,10 @@ class LowerType
     /// Otherwise, get the fixed layout information from reflection
     /// metadata.
     auto *descriptor = TC.getBuilder().getBuiltinTypeInfo(B);
-    if (descriptor == nullptr)
+    if (descriptor == nullptr) {
+      DEBUG(std::cerr << "No TypeInfo for builtin type: "; B->dump());
       return nullptr;
+    }
     return TC.makeTypeInfo<BuiltinTypeInfo>(descriptor);
   }
 
@@ -982,6 +1006,7 @@ class LowerType
         return TC.makeTypeInfo<BuiltinTypeInfo>(ImportedTypeDescriptor);
 
       // Otherwise, we're out of luck.
+      DEBUG(std::cerr << "No TypeInfo for nominal type: "; TR->dump());
       return nullptr;
     }
 
@@ -1009,7 +1034,7 @@ class LowerType
     case FieldDescriptorKind::ObjCProtocol:
     case FieldDescriptorKind::ClassProtocol:
     case FieldDescriptorKind::Protocol:
-      // Invalid field descriptor
+      DEBUG(std::cerr << "Invalid field descriptor: "; TR->dump());
       return nullptr;
     }
   }
@@ -1060,6 +1085,7 @@ class LowerType
   const TypeInfo *visitMetatypeTypeRef(const MetatypeTypeRef *M) {
     switch (HasSingletonMetatype().visit(M)) {
     case MetatypeRepresentation::Unknown:
+      DEBUG(std::cerr << "Unknown metatype representation: "; M->dump());
       return nullptr;
     case MetatypeRepresentation::Thin:
       return TC.getEmptyTypeInfo();
@@ -1079,7 +1105,7 @@ class LowerType
       for (auto *P : PC->getProtocols())
         builder.addProtocol(P);
     } else {
-      // Invalid TypeRef
+      DEBUG(std::cerr << "Invalid existential metatype: "; EM->dump());
       return nullptr;
     }
 
@@ -1114,8 +1140,10 @@ class LowerType
   const TypeInfo *
   rebuildStorageTypeInfo(const TypeInfo *TI, ReferenceKind Kind) {
     // If we can't lower the original storage type, give up.
-    if (TI == nullptr)
+    if (TI == nullptr) {
+      DEBUG(std::cerr << "Invalid reference type");
       return nullptr;
+    }
 
     // Simple case: Just change the reference kind
     if (auto *ReferenceTI = dyn_cast<ReferenceTypeInfo>(TI))
@@ -1156,6 +1184,7 @@ class LowerType
     }
 
     // Anything else -- give up
+    DEBUG(std::cerr << "Invalid reference type");
     return nullptr;
   }
 
@@ -1213,8 +1242,10 @@ const TypeInfo *TypeConverter::getClassInstanceTypeInfo(const TypeRef *TR,
                                                         unsigned start,
                                                         unsigned align) {
   const FieldDescriptor *FD = getBuilder().getFieldTypeInfo(TR);
-  if (FD == nullptr)
+  if (FD == nullptr) {
+    DEBUG(std::cerr << "No field descriptor: "; TR->dump());
     return nullptr;
+  }
 
   switch (FD->Kind) {
   case FieldDescriptorKind::Class:
@@ -1238,6 +1269,7 @@ const TypeInfo *TypeConverter::getClassInstanceTypeInfo(const TypeRef *TR,
   case FieldDescriptorKind::ClassProtocol:
   case FieldDescriptorKind::Protocol:
     // Invalid field descriptor.
+    DEBUG(std::cerr << "Invalid field descriptor: "; TR->dump());
     return nullptr;
   }
 }