AST: Introduce @_primaryAssociatedType attribute

Author: slavapestov

include/swift/AST/Attr.def

@@ -657,7 +657,10 @@ CONTEXTUAL_SIMPLE_DECL_ATTR(distributed, DistributedActor,
   APIBreakingToAdd | APIBreakingToRemove,
   118)
 
-// 119 is unused
+SIMPLE_DECL_ATTR(_primaryAssociatedType,
+  PrimaryAssociatedType, OnAssociatedType | UserInaccessible |
+  APIStableToAdd | ABIStableToAdd | APIBreakingToRemove | ABIStableToRemove,
+  119)
 
 SIMPLE_DECL_ATTR(_assemblyVision, EmitAssemblyVisionRemarks,
   OnFunc | UserInaccessible | NotSerialized | OnNominalType |

lib/Sema/TypeCheckAttr.cpp

@@ -273,6 +273,8 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
   void visitNoImplicitCopyAttr(NoImplicitCopyAttr *attr);
 
   void visitUnavailableFromAsyncAttr(UnavailableFromAsyncAttr *attr);
+
+  void visitPrimaryAssociatedTypeAttr(PrimaryAssociatedTypeAttr *attr);
 };
 
 } // end anonymous namespace
@@ -5777,6 +5779,10 @@ void AttributeChecker::visitUnavailableFromAsyncAttr(
   }
 }
 
+void AttributeChecker::visitPrimaryAssociatedTypeAttr(
+    PrimaryAssociatedTypeAttr *attr) {
+}
+
 namespace {
 
 class ClosureAttributeChecker

lib/Sema/TypeCheckDeclOverride.cpp

@@ -1564,6 +1564,9 @@ namespace  {
 
     UNINTERESTING_ATTR(TypeSequence)
     UNINTERESTING_ATTR(CompileTimeConst)
+
+    UNINTERESTING_ATTR(PrimaryAssociatedType)
+
 #undef UNINTERESTING_ATTR
 
     void visitAvailableAttr(AvailableAttr *attr) {