[c++20][clangd] Simplify code using the new `ConceptReference` nodes.

[massberg]

Summary

Directly traverse ConceptReferences in FindTarget.cpp.

There is no need for the extra logic for AutoTypeLocs in SemanticHightlighting.cpp as the concept information is stored in a ConceptReference which is now traversed.

[sammccall]

clang-tools-extra/clangd/FindTarget.cpp

1059–1061

I think this can just be VisitConceptReference, then no need to call into base

[massberg]

Use VisitConceptReference instead of TraverseConceptReference

clang-tools-extra/clangd/FindTarget.cpp

llvm::SmallVector<ReferenceLoc> refInStmt(const Stmt *S,
                                           const HeuristicResolver *Resolver) {
   struct Visitor : ConstStmtVisitor<Visitor> {
     Visitor(const HeuristicResolver *Resolver) : Resolver(Resolver) {}
 
     const HeuristicResolver *Resolver;
     // FIXME: handle more complicated cases: more ObjC, designated initializers.
     llvm::SmallVector<ReferenceLoc> Refs;
 
-    void VisitConceptSpecializationExpr(const ConceptSpecializationExpr *E) {
-      Refs.push_back(ReferenceLoc{E->getNestedNameSpecifierLoc(),
-                                  E->getConceptNameLoc(),
-                                  /*IsDecl=*/false,
-                                  {E->getNamedConcept()}});
-    }
-
     void VisitDeclRefExpr(const DeclRefExpr *E) {
       Refs.push_back(ReferenceLoc{E->getQualifierLoc(),
                                   E->getNameInfo().getLoc(),
                                   /*IsDecl=*/false,
                                   {E->getFoundDecl()}});
     }
 
     void VisitDependentScopeDeclRefExpr(const DependentScopeDeclRefExpr *E) {
bool TraverseObjCProtocolLoc(ObjCProtocolLoc ProtocolLoc) {
     return true;
   }
 
   bool TraverseConstructorInitializer(CXXCtorInitializer *Init) {
     visitNode(DynTypedNode::create(*Init));
     return RecursiveASTVisitor::TraverseConstructorInitializer(Init);
   }
 
-  bool TraverseTypeConstraint(const TypeConstraint *TC) {
-    // We want to handle all ConceptReferences but RAV is missing a
-    // polymorphic Visit or Traverse method for it, so we handle
-    // TypeConstraints specially here.
-    Out(ReferenceLoc{TC->getNestedNameSpecifierLoc(),
-                     TC->getConceptNameLoc(),
+  bool VisitConceptReference(ConceptReference *ConceptRef) {
+    Out(ReferenceLoc{ConceptRef->getNestedNameSpecifierLoc(),
+                     ConceptRef->getConceptNameLoc(),
                      /*IsDecl=*/false,
-                     {TC->getNamedConcept()}});
-    return RecursiveASTVisitor::TraverseTypeConstraint(TC);
+                     {ConceptRef->getNamedConcept()}});
+    return true;
   }
 
 private:
   /// Obtain information about a reference directly defined in \p N. Does not
   /// recurse into child nodes, e.g. do not expect references for constructor
   /// initializers
   ///
   /// Any of the fields in the returned structure can be empty, but not all of

clang-tools-extra/clangd/SemanticHighlighting.cpp

bool VisitMemberExpr(MemberExpr *E) {
     return true;
   }
 
   bool VisitTemplateSpecializationTypeLoc(TemplateSpecializationTypeLoc L) {
     H.addAngleBracketTokens(L.getLAngleLoc(), L.getRAngleLoc());
     return true;
   }
 
-  bool VisitAutoTypeLoc(AutoTypeLoc L) {
-    if (L.isConstrained()) {
-      H.addAngleBracketTokens(L.getLAngleLoc(), L.getRAngleLoc());
-      H.addToken(L.getConceptNameInfo().getLoc(), HighlightingKind::Concept);
-    }
-    return true;
-  }
-
   bool VisitFunctionDecl(FunctionDecl *D) {
     if (D->isOverloadedOperator()) {
       const auto AddOpDeclToken = [&](SourceLocation Loc) {
         auto &Token = H.addToken(Loc, HighlightingKind::Operator)
                           .addModifier(HighlightingModifier::Declaration);
         if (D->isThisDeclarationADefinition())
           Token.addModifier(HighlightingModifier::Definition);
       };