Improve "reference-to" message somewhat

Author: CodaFi

include/swift/AST/DiagnosticsSema.def

@@ -894,6 +894,8 @@ ERROR(precedence_group_redeclared,none,
       "precedence group redeclared", ())
 NOTE(previous_precedence_group_decl,none,
      "previous precedence group declaration here", ())
+NOTE(circular_reference_through_precedence_group, none,
+     "through reference to precedence group %0 here", (Identifier))
 
 //------------------------------------------------------------------------------
 // MARK: Expression Type Checking Errors

include/swift/AST/TypeCheckRequests.h

@@ -1449,11 +1449,15 @@ class InterfaceTypeRequest :
 };
 
 struct PrecedenceGroupDescriptor {
+  enum PathDirection : bool {
+    LowerThan = false,
+    HigherThan = true,
+  };
   DeclContext *dc;
   Identifier ident;
   SourceLoc nameLoc;
   // Exists for diagnostics. Does not contribute to the descriptor otherwise.
-  Optional<bool> pathDirection;
+  Optional<PathDirection> pathDirection;
 
   SourceLoc getLoc() const;
 

lib/AST/TypeCheckRequests.cpp

@@ -1039,15 +1039,16 @@ SourceLoc LookupPrecedenceGroupRequest::getNearestLoc() const {
 void LookupPrecedenceGroupRequest::diagnoseCycle(DiagnosticEngine &diags) const {
   auto &desc = std::get<0>(getStorage());
   if (auto pathDir = desc.pathDirection) {
-    diags.diagnose(desc.nameLoc, diag::precedence_group_cycle, *pathDir);
+    diags.diagnose(desc.nameLoc, diag::precedence_group_cycle, (bool)*pathDir);
   } else {
     diags.diagnose(desc.nameLoc, diag::circular_reference);
   }
 }
 
-void LookupPrecedenceGroupRequest::noteCycleStep(DiagnosticEngine &diags) const {
+void LookupPrecedenceGroupRequest::noteCycleStep(DiagnosticEngine &diag) const {
   auto &desc = std::get<0>(getStorage());
-  diags.diagnose(desc.nameLoc, diag::circular_reference_through);
+  diag.diagnose(desc.nameLoc,
+                 diag::circular_reference_through_precedence_group, desc.ident);
 }
 
 SourceLoc PrecedenceGroupDescriptor::getLoc() const {

lib/Sema/TypeCheckDecl.cpp

@@ -1860,14 +1860,15 @@ static void validatePrecedenceGroup(PrecedenceGroupDecl *PGD) {
     return;
 
   auto &Diags = PGD->getASTContext().Diags;
-  
+
   // Validate the higherThan relationships.
   bool addedHigherThan = false;
   for (auto &rel : PGD->getMutableHigherThan()) {
-    if (rel.Group) continue;
+    if (rel.Group)
+      continue;
 
-    PrecedenceGroupDescriptor desc{PGD->getDeclContext(), rel.Name,
-                                   rel.NameLoc, true};
+    PrecedenceGroupDescriptor desc{PGD->getDeclContext(), rel.Name, rel.NameLoc,
+                                   PrecedenceGroupDescriptor::HigherThan};
     auto group = evaluateOrDefault(PGD->getASTContext().evaluator,
                                    LookupPrecedenceGroupRequest{desc}, nullptr);
     if (group) {
@@ -1882,11 +1883,12 @@ static void validatePrecedenceGroup(PrecedenceGroupDecl *PGD) {
 
   // Validate the lowerThan relationships.
   for (auto &rel : PGD->getMutableLowerThan()) {
-    if (rel.Group) continue;
+    if (rel.Group)
+      continue;
 
     auto dc = PGD->getDeclContext();
-    PrecedenceGroupDescriptor desc{PGD->getDeclContext(), rel.Name,
-                                   rel.NameLoc, false};
+    PrecedenceGroupDescriptor desc{PGD->getDeclContext(), rel.Name, rel.NameLoc,
+                                   PrecedenceGroupDescriptor::LowerThan};
     auto group = evaluateOrDefault(PGD->getASTContext().evaluator,
                                    LookupPrecedenceGroupRequest{desc}, nullptr);
     bool hadError = false;
@@ -1906,8 +1908,7 @@ static void validatePrecedenceGroup(PrecedenceGroupDecl *PGD) {
     if (group &&
         group->getDeclContext()->getParentModule() == dc->getParentModule()) {
       if (!PGD->isInvalid()) {
-        Diags.diagnose(rel.NameLoc,
-                       diag::precedence_group_lower_within_module);
+        Diags.diagnose(rel.NameLoc, diag::precedence_group_lower_within_module);
         Diags.diagnose(group->getNameLoc(), diag::kind_declared_here,
                        DescriptiveDeclKind::PrecedenceGroup);
       }
@@ -1918,7 +1919,7 @@ static void validatePrecedenceGroup(PrecedenceGroupDecl *PGD) {
       PGD->setInvalid();
   }
 
-  // Try to catch trickier cycles that request evaluation alone can't.
+  // Try to diagnose trickier cycles that request evaluation alone can't catch.
   if (addedHigherThan)
     checkPrecedenceCircularity(Diags, PGD);
 }

test/decl/precedencegroup/circularity.swift

@@ -18,17 +18,17 @@ precedencegroup C0 {
   higherThan: C1 // expected-error {{cycle in 'higherThan' relation}}
 }
 precedencegroup C1 {
-  higherThan: C0 // expected-note{{through reference here}}
+  higherThan: C0 // expected-note{{through reference to precedence group 'C0' here}}
 }
 
 precedencegroup D0 {
   higherThan: D1 // expected-error {{cycle in 'higherThan' relation}}
 }
 precedencegroup D1 {
-  higherThan: D2 // expected-note{{through reference here}}
+  higherThan: D2 // expected-note{{through reference to precedence group 'D2' here}}
 }
 precedencegroup D2 {
-  higherThan: D0 // expected-note{{through reference here}}
+  higherThan: D0 // expected-note{{through reference to precedence group 'D0' here}}
 }
 
 precedencegroup E0 {