[clangd] Include "final" when printing class declaration

[tom-anders]

Summary

Fixes https://github.com/clangd/clangd/issues/1184

[sammccall]

clang/lib/AST/DeclPrinter.cpp

1010

isEffectivelyFinal returns true for
struct X { ~X() final; }

I don't think we want to print struct X final {} in that case.

Probably want to replicate the check for FinalAttr instead?

[tom-anders]

clang/lib/AST/DeclPrinter.cpp

1010

Agreed. Would probably make sense to add a bool hasFinalAttribute() const to CXXRecordDecl?

[sammccall]

clang/lib/AST/DeclPrinter.cpp

1010

I'm not sure such a method pays for itself, the abstraction it might provides over hasAttr() is:

• it handles the case where there's no definition... but maybe "return false" isn't the right thing to do in all circumstances?
• a simple hasFinal() could avoid thinking about syntactic details - but here we explicitly care about them.
• it hides the detail that final is stored as an attribute rather than e.g. a bit. This is the only piece that seems useful.

Given that, I think it's probably best here just to inline the logic, but I don't feel strongly.

[tom-anders]

Check for FinalAttr instead of using isEffectivelyFinal()

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

const std::function<void(HoverInfo &)> ExpectedBuilder;
          HI.Definition = "template <> class vector<int> {}";
        }},
       // Class template
       {R"cpp(
           template <template<typename, bool...> class C,
                     typename = char,
                     int = 0,
                     bool Q = false,
-                    class... Ts> class Foo {};
+                    class... Ts> class Foo final {};
           template <template<typename, bool...> class T>
           [[F^oo]]<T> foo;
           )cpp",
        [](HoverInfo &HI) {
          HI.NamespaceScope = "";
          HI.Name = "Foo";
          HI.Kind = index::SymbolKind::Class;
          HI.Definition =
              R"cpp(template <template <typename, bool...> class C, typename = char, int = 0,
           bool Q = false, class... Ts>
-class Foo {})cpp";
+class Foo final {})cpp";
          HI.TemplateParameters = {
              {{"template <typename, bool...> class"},
               std::string("C"),
               llvm::None},
              {{"typename"}, llvm::None, std::string("char")},
              {{"int"}, llvm::None, std::string("0")},
              {{"bool"}, std::string("Q"), std::string("false")},
              {{"class..."}, std::string("Ts"), llvm::None},

clang/lib/AST/DeclPrinter.cpp

if (auto S = dyn_cast<ClassTemplateSpecializationDecl>(D)) {
           if (const auto *TST =
                   dyn_cast<TemplateSpecializationType>(TSI->getType()))
             Args = TST->template_arguments();
       printTemplateArguments(
           Args, S->getSpecializedTemplate()->getTemplateParameters());
     }
   }
 
+  if (auto *Def = D->getDefinition()) {
+      if (D->hasAttr<FinalAttr>()) {
+          Out << " final";
+      }
+  }
+
   if (D->isCompleteDefinition()) {
     // Print the base classes
     if (D->getNumBases()) {
       Out << " : ";
       for (CXXRecordDecl::base_class_iterator Base = D->bases_begin(),
              BaseEnd = D->bases_end(); Base != BaseEnd; ++Base) {
         if (Base != D->bases_begin())
           Out << ", ";