NCGenerics: avoid synthesizing Equatable, etc.

While certain kinds of enums synthesize Equatable, Hashable, and
RawRepresentable conformances, we can't yet permit noncopyable types to
synthesize those until we upgrade those protocols themselves to not
require `Copyable` conformers. For example, Equatable needs to be
changed in the stdlib to be `protocol Equatable: ~Copyable`, etc.

I'm deferring upgrade work until a bit later.

Author: kavon

lib/AST/ProtocolConformance.cpp

@@ -1076,20 +1076,10 @@ void NominalTypeDecl::prepareConformanceTable() const {
   }
 
   SmallPtrSet<ProtocolDecl *, 2> protocols;
-  const bool haveNoncopyableGenerics =
-      ctx.LangOpts.hasFeature(Feature::NoncopyableGenerics);
-
   auto addSynthesized = [&](ProtocolDecl *proto) {
     if (!proto)
       return;
 
-    // No synthesized conformances for move-only nominals.
-    if (!haveNoncopyableGenerics && !canBeCopyable()) {
-      // assumption is Sendable gets synthesized elsewhere.
-      assert(!proto->isSpecificProtocol(KnownProtocolKind::Sendable));
-      return;
-    }
-
     if (protocols.count(proto) == 0) {
       ConformanceTable->addSynthesizedConformance(
           mutableThis, proto, mutableThis);
@@ -1099,12 +1089,22 @@ void NominalTypeDecl::prepareConformanceTable() const {
 
   // Synthesize the unconditional conformances to invertible protocols.
   // For conditional ones, see findSynthesizedConformances .
-  if (haveNoncopyableGenerics) {
+  if (ctx.LangOpts.hasFeature(Feature::NoncopyableGenerics)) {
+    bool missingOne = false;
     for (auto ip : InvertibleProtocolSet::full()) {
       auto invertible = getMarking(ip);
       if (!invertible.getInverse() || bool(invertible.getPositive()))
         addSynthesized(ctx.getProtocol(getKnownProtocolKind(ip)));
+      else
+        missingOne = true;
     }
+
+    // FIXME: rdar://122289155 (NCGenerics: convert Equatable, Hashable, and RawRepresentable to ~Copyable.)
+    if (missingOne)
+      return;
+
+  } else if (!canBeCopyable()) {
+    return; // No synthesized conformances for move-only nominals.
   }
 
   // Add protocols for any synthesized protocol attributes.