[clangd] Support typeHierarchy/resolve for children of parents as well

[nridge]

Summary

The initial implementation of typeHierarchy/resolve only supported
cases where an initial request was made for children, and then
typeHierarchy/resolve was used to get additional levels of children.

However, a client may also want to make an initial request for
parents, and then show other children of those parents, so support
typeHierarchy/resolve for items returned in response to a request
for parents as well.

[sammccall]

clang-tools-extra/clangd/XRefs.cpp

1233

nit: use getSymbolID from AST.h instead

[nridge]

Address nit

[sammccall]

May have broken tests: http://lab.llvm.org:8011/builders/clang-x86_64-debian-fast/builds/30458/steps/test-check-all/logs/FAIL%3A%20Clangd%3A%3A%20type-hierarchy.test

[nridge]

In D81845#2093056, @sammccall wrote:

May have broken tests: http://lab.llvm.org:8011/builders/clang-x86_64-debian-fast/builds/30458/steps/test-check-all/logs/FAIL%3A%20Clangd%3A%3A%20type-hierarchy.test

Sorry about that, pushed a follow up to fix the lit test: https://github.com/llvm/llvm-project/commit/d1505233c85360bf3d9ab07af803b2bb478547a6

clang-tools-extra/clangd/XRefs.cpp

declToTypeHierarchyItem(ASTContext &Ctx, const NamedDecl &ND,
   if (!THI.range.contains(THI.selectionRange)) {
     // 'selectionRange' must be contained in 'range', so in cases where clang
     // reports unrelated ranges we need to reconcile somehow.
     THI.range = THI.selectionRange;
   }
 
   THI.uri = URIForFile::canonicalize(*FilePath, *TUPath);
 
+  // Compute the SymbolID and store it in the 'data' field.
+  // This allows typeHierarchy/resolve to be used to
+  // resolve children of items returned in a previous request
+  // for parents.
+  if (auto ID = getSymbolID(&ND)) {
+    THI.data = ID->str();
+  }
+
   return THI;
 }
 
 static Optional<TypeHierarchyItem>
 symbolToTypeHierarchyItem(const Symbol &S, const SymbolIndex *Index,
                           PathRef TUPath) {
   auto Loc = symbolToLocation(S, TUPath);
   if (!Loc) {