[clangd] Type hierarchy: don't resolve parents if the client only asked for children

[nridge]

Summary

Also reorganize the code for computing supertypes to make it more symmetric to subtypes.

[nridge]

This is an issue I noticed while writing the unit test for D64308.

[kadircet]

clang-tools-extra/clangd/XRefs.cpp

1238

having a function named getTypeAncestors with a parameter ResolveParents doesn't make much sense. maybe move the check to caller side and simply don't call it if we are not interested in parents?

I think it makes sense to make this part also similar to subtypes:

• let's generate the item in here with Optional<TypeHierarchyItem> Result = declToTypeHierarchyItem(ASTCtx, CXXRD);, which is used by both parents and children.
• bail out if we couldn't get the item.
• fill in parents if need be
• fill in children if need be

WDYT?

[nridge]

Address review comment

[nridge]

clang-tools-extra/clangd/XRefs.cpp

1238

Agreed, this makes the code cleaner.

[nridge]

(Changed reviewer to Kadir as he reviewed the previous version.)

[kadircet]

LGTM, thanks!

clang-tools-extra/clangd/XRefs.cpp

Index->relations(Req, [&](const SymbolID &Subject, const Symbol &Object) {
     }
   });
 }
 
 using RecursionProtectionSet = llvm::SmallSet<const CXXRecordDecl *, 4>;
 
 static Optional<TypeHierarchyItem>
 getTypeAncestors(const CXXRecordDecl &CXXRD, ASTContext &ASTCtx,
-                 RecursionProtectionSet &RPSet) {
+                 RecursionProtectionSet &RPSet, bool ResolveParents = true) {
   Optional<TypeHierarchyItem> Result = declToTypeHierarchyItem(ASTCtx, CXXRD);
-  if (!Result)
+  if (!Result || !ResolveParents)
     return Result;
 
   Result->parents.emplace();
 
   // typeParents() will replace dependent template specializations
   // with their class template, so to avoid infinite recursion for
   // certain types of hierarchies, keep the templates encountered
   // along the parent chain in a set, and stop the recursion if one

 getTypeHierarchy(ParsedAST &AST, Position Pos, int ResolveLevels,
                  TypeHierarchyDirection Direction, const SymbolIndex *Index,
                  PathRef TUPath) {
   const CXXRecordDecl *CXXRD = findRecordTypeAt(AST, Pos);
   if (!CXXRD)
     return llvm::None;
 
   RecursionProtectionSet RPSet;
+  bool ResolveParents = (Direction == TypeHierarchyDirection::Parents ||
+                         Direction == TypeHierarchyDirection::Both);
   Optional<TypeHierarchyItem> Result =
-      getTypeAncestors(*CXXRD, AST.getASTContext(), RPSet);
+      getTypeAncestors(*CXXRD, AST.getASTContext(), RPSet, ResolveParents);
   if (!Result)
     return Result;
 
   if ((Direction == TypeHierarchyDirection::Children ||
        Direction == TypeHierarchyDirection::Both) &&
       ResolveLevels > 0) {
     Result->children.emplace();
 

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

)cpp");
   auto Index = TU.index();
 
   llvm::Optional<TypeHierarchyItem> Result = getTypeHierarchy(
       AST, Source.point(), /*ResolveLevels=*/1,
       TypeHierarchyDirection::Children, Index.get(), "/clangd-test/TestTU.cpp");
   ASSERT_TRUE(bool(Result));
   EXPECT_THAT(
       *Result,
-      AllOf(WithName("Parent"), WithKind(SymbolKind::Struct), Parents(),
+      AllOf(WithName("Parent"), WithKind(SymbolKind::Struct),
+            ParentsNotResolved(),
             Children(AllOf(WithName("Child1"), WithKind(SymbolKind::Struct),
                            ParentsNotResolved(), ChildrenNotResolved()))));
 
   resolveTypeHierarchy((*Result->children)[0], /*ResolveLevels=*/1,
                        TypeHierarchyDirection::Children, Index.get());
 
   EXPECT_THAT(
       (*Result->children)[0],