[clangd] Fix hover crash on invalid decls

[kadircet]

Summary

This also changes the way we display Size and Offset to be independent.

[kadircet]

Inline OffsetBits

[sammccall]

Thanks!

clang-tools-extra/clangd/Hover.cpp

if (auto *RD = llvm::dyn_cast<RecordDecl>(&ND)) {
     return;
   }
 
   if (const auto *FD = llvm::dyn_cast<FieldDecl>(&ND)) {
     const auto *Record = FD->getParent();
     if (Record)
       Record = Record->getDefinition();
     if (Record && !Record->isDependentType()) {
-      uint64_t OffsetBits = Ctx.getFieldOffset(FD);
-      if (auto Size = Ctx.getTypeSizeInCharsIfKnown(FD->getType())) {
+      if (auto Size = Ctx.getTypeSizeInCharsIfKnown(FD->getType()))
         HI.Size = Size->getQuantity();
-        HI.Offset = OffsetBits / 8;
-      }
+      if (!FD->isInvalidDecl())
+        HI.Offset = Ctx.getFieldOffset(FD) / 8;
     }
     return;
   }
 }
 
 // If N is passed as argument to a function, fill HI.CalleeArgInfo with
 // information about that argument.
 void maybeAddCalleeArgInfo(const SelectionTree::Node *N, HoverInfo &HI,

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

class Foo {})cpp";
          HI.CalleeArgInfo.emplace();
          HI.CalleeArgInfo->Name = "arg_a";
          HI.CalleeArgInfo->Type = "int";
          HI.CalleeArgInfo->Default = "3";
          HI.CallPassType.emplace();
          HI.CallPassType->PassBy = PassMode::Value;
          HI.CallPassType->Converted = false;
        }},
+      {// Dont crash on invalid decl
+       R"cpp(
+        // error-ok
+        struct Foo {
+          Bar [[x^x]];
+        };)cpp",
+       [](HoverInfo &HI) {
+         HI.Name = "xx";
+         HI.Kind = index::SymbolKind::Field;
+         HI.NamespaceScope = "";
+         HI.Definition = "int xx";
+         HI.LocalScope = "Foo::";
+         HI.Size = 4;
+         HI.Type = "int";
+         HI.AccessSpecifier = "public";
+       }},
   };
   for (const auto &Case : Cases) {
     SCOPED_TRACE(Case.Code);
 
     Annotations T(Case.Code);
     TestTU TU = TestTU::withCode(T.code());
     TU.ExtraArgs.push_back("-std=c++17");
     // Types might be different depending on the target triplet, we chose a