[clangd] Drop returntype/type when hovering over type-ish names

[kadircet]

Summary

Some names, e.g. constructor/destructor/conversions, already contain
the type info, no need to duplicate them in the hoverinfo.

Fixes https://github.com/clangd/clangd/issues/252

[merge_guards_bot]

Unit tests: pass. 62057 tests passed, 0 failed and 784 were skipped.

clang-tidy: unknown.

clang-format: pass.

Build artifacts: diff.json, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

clang-tools-extra/clangd/Hover.cpp

if (!PVD->getName().empty())
       P.Name = PVD->getNameAsString();
     if (PVD->hasDefaultArg()) {
       P.Default.emplace();
       llvm::raw_string_ostream Out(*P.Default);
       PVD->getDefaultArg()->printPretty(Out, nullptr, Policy);
     }
   }
 
-  if (const auto *CCD = llvm::dyn_cast<CXXConstructorDecl>(FD)) {
-    // Constructor's "return type" is the class type.
-    HI.ReturnType = declaredType(CCD->getParent()).getAsString(Policy);
-    // Don't provide any type for the constructor itself.
-  } else if (llvm::isa<CXXDestructorDecl>(FD)) {
-    HI.ReturnType = "void";
-  } else {
-    HI.ReturnType = printType(FD->getReturnType(), Policy);
+  // We don't want any type info, if name already contains it. This is true for
+  // constructors/destructors and conversion operators.
+  const auto NK = FD->getDeclName().getNameKind();
+  if (NK == DeclarationName::CXXConstructorName ||
+      NK == DeclarationName::CXXDestructorName ||
+      NK == DeclarationName::CXXConversionFunctionName)
+    return;
 
-    QualType QT = FD->getType();
-    if (const VarDecl *VD = llvm::dyn_cast<VarDecl>(D)) // Lambdas
-      QT = VD->getType().getDesugaredType(D->getASTContext());
-    HI.Type = printType(QT, Policy);
-  }
+  HI.ReturnType = printType(FD->getReturnType(), Policy);
   // FIXME: handle variadics.
 }
 
 llvm::Optional<std::string> printExprValue(const Expr *E,
                                            const ASTContext &Ctx) {
   Expr::EvalResult Constant;
   // Evaluating [[foo]]() as "&foo" isn't useful, and prevents us walking up
   // to the enclosing call.

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

class Foo {})cpp";
           template<typename, typename=void> struct X;
           template<typename T> struct X<T*>{ [[^X]](); };
           )cpp",
        [](HoverInfo &HI) {
          HI.NamespaceScope = "";
          HI.Name = "X";
          HI.LocalScope = "X<T *>::"; // FIXME: X<T *, void>::
          HI.Kind = index::SymbolKind::Constructor;
-         HI.ReturnType = "X<T *>";
          HI.Definition = "X()";
          HI.Parameters.emplace();
        }},
       {"class X { [[^~]]X(); };", // FIXME: Should be [[~X]]()
        [](HoverInfo &HI) {
          HI.NamespaceScope = "";
          HI.Name = "~X";
          HI.LocalScope = "X::";
          HI.Kind = index::SymbolKind::Destructor;
-         HI.ReturnType = "void";
          HI.Definition = "~X()";
          HI.Parameters.emplace();
        }},
+      {"class X { operator [[in^t]](); };",
+       [](HoverInfo &HI) {
+         HI.NamespaceScope = "";
+         HI.Name = "operator int";
+         HI.LocalScope = "X::";
+         HI.Kind = index::SymbolKind::ConversionFunction;
+         HI.Definition = "operator int()";
+         HI.Parameters.emplace();
+       }},
 
       // auto on lambda
       {R"cpp(
         void foo() {
           [[au^to]] lamb = []{};
         }
         )cpp",
        [](HoverInfo &HI) {