AST: Tailored circularity diagnostic for StructuralTypeRequest

Author: slavapestov

include/swift/AST/TypeCheckRequests.h

@@ -874,6 +874,7 @@ class StructuralTypeRequest :
 public:
   // Caching.
   bool isCached() const { return true; }
+  void diagnoseCycle(DiagnosticEngine &diags) const;
 };
 
 /// Request the fragile function kind for the context.

lib/AST/TypeCheckRequests.cpp

@@ -819,6 +819,17 @@ void UnderlyingTypeRequest::diagnoseCycle(DiagnosticEngine &diags) const {
                  aliasDecl->getName());
 }
 
+//----------------------------------------------------------------------------//
+// StructuralTypeRequest computation.
+//----------------------------------------------------------------------------//
+
+void StructuralTypeRequest::diagnoseCycle(DiagnosticEngine &diags) const {
+  auto aliasDecl = std::get<0>(getStorage());
+  diags.diagnose(aliasDecl, diag::recursive_decl_reference,
+                 aliasDecl->getDescriptiveKind(),
+                 aliasDecl->getName());
+}
+
 //----------------------------------------------------------------------------//
 // EnumRawValuesRequest computation.
 //----------------------------------------------------------------------------//