[clangd] Semantic highlighting for dependent template name in template argument

[nridge]

Summary

Fixes https://github.com/clangd/clangd/issues/484

[hokein]

clang-tools-extra/clangd/SemanticHighlighting.cpp

305

nit: move the trailing ; to a new line.

[nridge]

clang-tools-extra/clangd/SemanticHighlighting.cpp

305

I have done this, but clang-format moves it back... do we really want to fight wit it?

[nridge]

Address nit

[nridge]

clang-tools-extra/clangd/SemanticHighlighting.cpp

305

I wrote it as:

default:
  break;

instead, I think that may be more idiomatic anyways.

clang-tools-extra/clangd/SemanticHighlighting.cpp

public:
   }
 
   bool VisitDependentTemplateSpecializationTypeLoc(
       DependentTemplateSpecializationTypeLoc L) {
     H.addToken(L.getTemplateNameLoc(), HighlightingKind::DependentType);
     return true;
   }
 
+  bool TraverseTemplateArgumentLoc(TemplateArgumentLoc L) {
+    switch (L.getArgument().getKind()) {
+    case TemplateArgument::Template:
+    case TemplateArgument::TemplateExpansion:
+      H.addToken(L.getTemplateNameLoc(), HighlightingKind::DependentType);
+      break;
+    default:
+      break;
+    }
+    return RecursiveASTVisitor::TraverseTemplateArgumentLoc(L);
+  }
+
   // findExplicitReferences will walk nested-name-specifiers and
   // find anything that can be resolved to a Decl. However, non-leaf
   // components of nested-name-specifiers which are dependent names
   // (kind "Identifier") cannot be resolved to a decl, so we visit
   // them here.
   bool TraverseNestedNameSpecifierLoc(NestedNameSpecifierLoc Q) {
     if (NestedNameSpecifier *NNS = Q.getNestedNameSpecifier()) {
       if (NNS->getKind() == NestedNameSpecifier::Identifier)

clang-tools-extra/clangd/unittests/SemanticHighlightingTests.cpp

)cpp",
           requires($TemplateParameter[[T]] $Parameter[[F]]) {
             $Parameter[[F]].$DependentName[[foo]]();
           };
       template <typename $TemplateParameter[[T]]>
           requires $Concept[[Fooable]]<$TemplateParameter[[T]]>
       void $Function[[bar]]($TemplateParameter[[T]] $Parameter[[F]]) {
         $Parameter[[F]].$DependentName[[foo]]();
       }
+    )cpp",
+      // Dependent template name
+      R"cpp(
+      template <template <typename> class> struct $Class[[A]] {};
+      template <typename $TemplateParameter[[T]]>
+      using $Typedef[[W]] = $Class[[A]]<
+        $TemplateParameter[[T]]::template $DependentType[[Waldo]]
+      >;
     )cpp"};
   for (const auto &TestCase : TestCases) {
     checkHighlightings(TestCase);
   }
 
   checkHighlightings(R"cpp(
     class $Class[[A]] {
       #include "imp.h"