AST: Don't add duplicate synthesized conformances

If an enum has a raw type, and a SynthesizedProtocolAttr, don't add
two duplicate conformances, since that triggers an assertion.

Instead, make sure to only add each conformance once. We cannot just
drop the SynthesizedProtocolAttr in this case, because we need to
pull the LazyConformanceLoader out of it.

Author: slavapestov

lib/AST/ProtocolConformance.cpp

@@ -817,37 +817,37 @@ void NominalTypeDecl::prepareConformanceTable() const {
     return;
   }
 
-  // Add any synthesized conformances.
+  SmallPtrSet<ProtocolDecl *, 2> protocols;
+
+  auto addSynthesized = [&](KnownProtocolKind kind) {
+    if (auto *proto = getASTContext().getProtocol(kind)) {
+      if (protocols.count(proto) == 0) {
+        ConformanceTable->addSynthesizedConformance(mutableThis, proto);
+        protocols.insert(proto);
+      }
+    }
+  };
+
+  // Add protocols for any synthesized protocol attributes.
+  for (auto attr : getAttrs().getAttributes<SynthesizedProtocolAttr>()) {
+    addSynthesized(attr->getProtocolKind());
+  }
+
+  // Add any implicit conformances.
   if (auto theEnum = dyn_cast<EnumDecl>(mutableThis)) {
     if (theEnum->hasCases() && theEnum->hasOnlyCasesWithoutAssociatedValues()) {
       // Simple enumerations conform to Equatable.
-      if (auto equatable = ctx.getProtocol(KnownProtocolKind::Equatable)) {
-        ConformanceTable->addSynthesizedConformance(mutableThis, equatable);
-      }
+      addSynthesized(KnownProtocolKind::Equatable);
 
       // Simple enumerations conform to Hashable.
-      if (auto hashable = getASTContext().getProtocol(
-                            KnownProtocolKind::Hashable)) {
-        ConformanceTable->addSynthesizedConformance(mutableThis, hashable);
-      }
+      addSynthesized(KnownProtocolKind::Hashable);
     }
 
     // Enumerations with a raw type conform to RawRepresentable.
     if (resolver)
       resolver->resolveRawType(theEnum);
     if (theEnum->hasRawType()) {
-      if (auto rawRepresentable =
-            ctx.getProtocol(KnownProtocolKind::RawRepresentable)) {
-        ConformanceTable->addSynthesizedConformance(mutableThis,
-                                                    rawRepresentable);
-      }
-    }
-  }
-
-  // Add protocols for any synthesized protocol attributes.
-  for (auto attr : getAttrs().getAttributes<SynthesizedProtocolAttr>()) {
-    if (auto proto = getASTContext().getProtocol(attr->getProtocolKind())) {
-      ConformanceTable->addSynthesizedConformance(mutableThis, proto);
+      addSynthesized(KnownProtocolKind::RawRepresentable);
     }
   }
 }