Ensure that Superclass Requirements Appear First in Minimal Protocol Composites

The requirements are not always going to appear with superclass constraints last, so we still need to ensure that superclass bounds wind up at the head of the set of members.

Author: CodaFi

lib/AST/Type.cpp

@@ -4014,12 +4014,17 @@ CanType ProtocolCompositionType::getMinimalCanonicalType(
     return Reqs.front().getSecondType()->getCanonicalType();
   }
 
+  Type superclass;
   llvm::SmallVector<Type, 2> MinimalMembers;
   bool MinimalHasExplicitAnyObject = false;
   for (const auto &Req : Reqs) {
     switch (Req.getKind()) {
-    case RequirementKind::Conformance:
     case RequirementKind::Superclass:
+      assert((!superclass || superclass->isEqual(Req.getSecondType()))
+             && "Multiple distinct superclass constraints!");
+      superclass = Req.getSecondType();
+      break;
+    case RequirementKind::Conformance:
       MinimalMembers.push_back(Req.getSecondType());
       break;
     case RequirementKind::Layout:
@@ -4030,6 +4035,11 @@ CanType ProtocolCompositionType::getMinimalCanonicalType(
     }
   }
 
+  // Ensure any superclass bounds appears first regardless of its order among
+  // the signature's requirements.
+  if (superclass)
+    MinimalMembers.insert(MinimalMembers.begin(), superclass->getCanonicalType());
+
   // The resulting composition is necessarily canonical.
   return CanType(build(Ctx, MinimalMembers, MinimalHasExplicitAnyObject));
 }