[clangd] Don't show header for namespace decl in Hover

[hokein]

Summary

The header for namespace symbol is barely useful.

[VitaNuo]

Thanks!

clang-tools-extra/clangd/Hover.cpp

if (const SelectionTree::Node *N = ST.commonAncestor()) {
         HI = getHoverContents(DeclToUse, PP, Index, TB);
         // Layout info only shown when hovering on the field/class itself.
         if (DeclToUse == N->ASTNode.get<Decl>())
           addLayoutInfo(*DeclToUse, *HI);
         // Look for a close enclosing expression to show the value of.
         if (!HI->Value)
           HI->Value = printExprValue(N, AST.getASTContext()).PrintedValue;
         maybeAddCalleeArgInfo(N, *HI, PP);
-        maybeAddSymbolProviders(AST, *HI, include_cleaner::Symbol{*DeclToUse});
+
+        if (!isa<NamespaceDecl>(DeclToUse))
+          maybeAddSymbolProviders(AST, *HI,
+                                  include_cleaner::Symbol{*DeclToUse});
       } else if (const Expr *E = N->ASTNode.get<Expr>()) {
         HoverCountMetric.record(1, "expr");
         HI = getHoverContents(N, E, AST, PP, Index);
       } else if (const Attr *A = N->ASTNode.get<Attr>()) {
         HoverCountMetric.record(1, "attribute");
         HI = getHoverContents(A, AST);
       }
       // FIXME: support hovers for other nodes?

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

const std::function<void(HoverInfo &)> ExpectedBuilder;
                // Hover selects the underlying decl of the using decl
                {R"cpp(
                   #include "foo.h"
                   namespace ns {
                     using ::Foo;
                   }
                   ns::F^oo d;
                 )cpp",
-                [](HoverInfo &HI) { HI.Provider = "\"foo.h\""; }}};
+                [](HoverInfo &HI) { HI.Provider = "\"foo.h\""; }},
+                {R"cpp(
+                  namespace foo {};
+                  using namespace fo^o;
+                )cpp",
+                [](HoverInfo &HI) { HI.Provider = ""; }},
+                };
 
   for (const auto &Case : Cases) {
     Annotations Code{Case.Code};
     SCOPED_TRACE(Code.code());
 
     TestTU TU;
     TU.Filename = "foo.cpp";
     TU.Code = Code.code();