[Diagnostics] Use the educational note name for the category name

Author: DougGregor

lib/AST/DiagnosticEngine.cpp

@@ -1337,6 +1337,7 @@ DiagnosticEngine::diagnosticInfoForDiagnostic(const Diagnostic &diagnostic,
 
   auto groupID = diagnostic.getGroupID();
   StringRef Category;
+  const char * const *associatedNotes = nullptr;
   if (isAPIDigesterBreakageDiagnostic(diagnostic.getID()))
     Category = "api-digester-breaking-change";
   else if (isNoUsageDiagnostic(diagnostic.getID()))
@@ -1345,6 +1346,10 @@ DiagnosticEngine::diagnosticInfoForDiagnostic(const Diagnostic &diagnostic,
     Category = getDiagGroupInfoByID(groupID).name;
   else if (isDeprecationDiagnostic(diagnostic.getID()))
     Category = "deprecation";
+  else if ((associatedNotes = educationalNotes[(uint32_t)diagnostic.getID()]) &&
+           *associatedNotes) {
+    Category = llvm::sys::path::stem(*associatedNotes);
+  }
 
   auto fixIts = diagnostic.getFixIts();
   if (loc.isValid()) {

test/diagnostics/educational_notes_serialization.swift

@@ -7,13 +7,13 @@
 
 typealias Fn = () -> ()
 extension Fn {}
-// CHECK: [[@LINE-1]]:1: error: non-nominal type 'Fn' (aka '() -> ()') cannot be extended [{{.*}}nominal-types.md] []
+// CHECK: [[@LINE-1]]:1: error: non-nominal type 'Fn' (aka '() -> ()') cannot be extended [{{.*}}nominal-types.md] [nominal-types]
 
 
 // Shares the flag record with `Fn`
 typealias Dup = () -> ()
 extension Dup {}
-// CHECK: [[@LINE-1]]:1: error: non-nominal type 'Dup' (aka '() -> ()') cannot be extended [{{.*}}nominal-types.md] []
+// CHECK: [[@LINE-1]]:1: error: non-nominal type 'Dup' (aka '() -> ()') cannot be extended [{{.*}}nominal-types.md] [nominal-types]
 
 do {
   func noNote(_: Int) {}