[clangd] Replace HighlightingKind::NumKinds with LastKind. NFC

[ilya-biryukov]

Summary

The latter simplifies the client code by avoiding the need to handle it
as a separate case statement.

[hokein]

LGTM, though I think the current implementation is a common pattern.

[ilya-biryukov]

In D67277#1662669, @hokein wrote:

LGTM, though I think the current implementation is a common pattern.

Thanks.

It's indeed a common pattern. The problem is that it forces clients to handle this extra case in every switch statement (otherwise we get compiler warnings).
LastKind avoids this, therefore it's arguably a little better for the clients.

clang-tools-extra/clangd/ClangdLSPServer.cpp

CompletionItemKindBitset defaultCompletionItemKinds() {
   return Defaults;
 }
 
 // Build a lookup table (HighlightingKind => {TextMate Scopes}), which is sent
 // to the LSP client.
 std::vector<std::vector<std::string>> buildHighlightScopeLookupTable() {
   std::vector<std::vector<std::string>> LookupTable;
   // HighlightingKind is using as the index.
-  for (int KindValue = 0; KindValue < (int)HighlightingKind::NumKinds;
+  for (int KindValue = 0; KindValue <= (int)HighlightingKind::LastKind;
        ++KindValue)
     LookupTable.push_back({toTextMateScope((HighlightingKind)(KindValue))});
   return LookupTable;
 }
 
 } // namespace
 
 // MessageHandler dispatches incoming LSP messages.

clang-tools-extra/clangd/SemanticHighlighting.h

enum class HighlightingKind {
   Class,
   Enum,
   EnumConstant,
   Namespace,
   TemplateParameter,
   Primitive,
   Macro,
 
-  NumKinds,
+  LastKind = Macro
 };
 llvm::raw_ostream& operator<<(llvm::raw_ostream &OS, HighlightingKind K);
 
 // Contains all information needed for the highlighting a token.
 struct HighlightingToken {
   HighlightingKind Kind;
   Range R;
 };

clang-tools-extra/clangd/SemanticHighlighting.cpp

llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, HighlightingKind K) {
   case HighlightingKind::Namespace:
     return OS << "Namespace";
   case HighlightingKind::TemplateParameter:
     return OS << "TemplateParameter";
   case HighlightingKind::Primitive:
     return OS << "Primitive";
   case HighlightingKind::Macro:
     return OS << "Macro";
-  case HighlightingKind::NumKinds:
-    llvm_unreachable("NumKinds is not a valid HighlightingKind");
   }
+  llvm_unreachable("invalid HighlightingKind");
 }
 
 std::vector<LineHighlightings>
 diffHighlightings(ArrayRef<HighlightingToken> New,
                   ArrayRef<HighlightingToken> Old) {
   assert(std::is_sorted(New.begin(), New.end()) &&
          "New must be a sorted vector");
   assert(std::is_sorted(Old.begin(), Old.end()) &&
llvm::StringRef toTextMateScope(HighlightingKind Kind) {
   case HighlightingKind::Namespace:
     return "entity.name.namespace.cpp";
   case HighlightingKind::TemplateParameter:
     return "entity.name.type.template.cpp";
   case HighlightingKind::Primitive:
     return "storage.type.primitive.cpp";
   case HighlightingKind::Macro:
     return "entity.name.function.preprocessor.cpp";
-  case HighlightingKind::NumKinds:
-    llvm_unreachable("must not pass NumKinds to the function");
   }
   llvm_unreachable("unhandled HighlightingKind");
 }
 
 } // namespace clangd
 } // namespace clang