Merge remote-tracking branch 'origin/master' into master-next

lib/AST/ASTPrinter.cpp

@@ -203,7 +203,8 @@ struct SynthesizedExtensionAnalyzer::Implementation {
   unsigned countInherits(ExtensionDecl *ED) {
     unsigned Count = 0;
     for (auto TL : ED->getInherited()) {
-      if (shouldPrint(TL.getType()->getAnyNominal(), Options))
+      auto *nominal = TL.getType()->getAnyNominal();
+      if (nominal && shouldPrint(nominal, Options))
         Count ++;
     }
     return Count;

lib/AST/Decl.cpp

@@ -2106,9 +2106,42 @@ bool NominalTypeDecl::derivesProtocolConformance(ProtocolDecl *protocol) const {
       return isObjC() && enumDecl->hasCases()
           && enumDecl->hasOnlyCasesWithoutAssociatedValues();
 
+    // Enums without associated values and enums with a raw type of String
+    // or Int can explicitly derive CodingKey conformance.
+    case KnownProtocolKind::CodingKey: {
+      Type rawType = enumDecl->getRawType();
+      if (rawType) {
+        auto parentDC = enumDecl->getDeclContext();
+        ASTContext &C = parentDC->getASTContext();
+
+        auto nominal = rawType->getAnyNominal();
+        return nominal == C.getStringDecl() || nominal == C.getIntDecl();
+      }
+
+      // hasOnlyCasesWithoutAssociatedValues will return true for empty enums;
+      // empty enumas are allowed to conform as well.
+      return enumDecl->hasOnlyCasesWithoutAssociatedValues();
+    }
+
     default:
       return false;
     }
+  } else if (isa<StructDecl>(this) || isa<ClassDecl>(this)) {
+    // Structs and classes can explicitly derive Encodable and Decodable
+    // conformance (explicitly meaning we can synthesize an implementation if
+    // a type conforms manually).
+    if (*knownProtocol == KnownProtocolKind::Encodable ||
+        *knownProtocol == KnownProtocolKind::Decodable) {
+      // FIXME: This is not actually correct. We cannot promise to always
+      // provide a witness here for all structs and classes. Unfortunately,
+      // figuring out whether this is actually possible requires much more
+      // context -- a TypeChecker and the parent decl context at least -- and is
+      // tightly coupled to the logic within DerivedConformance.
+      // This unfortunately means that we expect a witness even if one will not
+      // be produced, which requires DerivedConformance::deriveCodable to output
+      // its own diagnostics.
+      return true;
+    }
   }
   return false;
 }