[lldb] Add SBType::FindDirectNestedType() function (#68705)

This patch adds a `SBType::FindDirectNestedType(name)` function which performs a non-recursive search in given class for a type with specified name. The intent is to perform a fast search in debug info, so that it can be used in formatters, and let them remain responsive.

This is driven by my work on formatters for Clang and LLVM types. In particular, by [`PointerIntPairInfo::MaskAndShiftConstants`](https://github.com/llvm/llvm-project/blob/cde9f9df79805a0850310870d6dcc64004292727/llvm/include/llvm/ADT/PointerIntPair.h#L174C16-L174C16), which is required to extract pointer and integer from `PointerIntPair`.

Related Discourse thread: https://discourse.llvm.org/t/traversing-member-types-of-a-type/72452

Author: Endilll

lldb/bindings/interface/SBTypeDocstrings.i

@@ -720,6 +720,14 @@ SBType supports the eq/ne operator. For example,::
     "
 ) lldb::SBType::GetTypeFlags;
 
+%feature("docstring",
+    "Searches for a directly nested type that has the provided name.
+
+    Returns the type if it was found.
+    Returns invalid type if nothing was found.
+    "
+) lldb::SBType::FindDirectNestedType;
+
 %feature("docstring",
 "Represents a list of :py:class:`SBType` s.
 

lldb/include/lldb/API/SBType.h

@@ -215,6 +215,8 @@ class SBType {
   bool GetDescription(lldb::SBStream &description,
                       lldb::DescriptionLevel description_level);
 
+  lldb::SBType FindDirectNestedType(const char *name);
+
   lldb::SBType &operator=(const lldb::SBType &rhs);
 
   bool operator==(lldb::SBType &rhs);

lldb/include/lldb/Symbol/Type.h

@@ -304,6 +304,8 @@ class TypeImpl {
   bool GetDescription(lldb_private::Stream &strm,
                       lldb::DescriptionLevel description_level);
 
+  CompilerType FindDirectNestedType(llvm::StringRef name);
+
 private:
   bool CheckModule(lldb::ModuleSP &module_sp) const;
   bool CheckExeModule(lldb::ModuleSP &module_sp) const;

lldb/include/lldb/Symbol/TypeSystem.h

@@ -142,6 +142,10 @@ class TypeSystem : public PluginInterface,
 
   virtual lldb::LanguageType DeclContextGetLanguage(void *opaque_decl_ctx) = 0;
 
+  /// Returns the direct parent context of specified type
+  virtual CompilerDeclContext
+  GetCompilerDeclContextForType(const CompilerType &type);
+
   // Tests
 #ifndef NDEBUG
   /// Verify the integrity of the type to catch CompilerTypes that mix

lldb/source/API/SBType.cpp

@@ -586,6 +586,14 @@ lldb::TemplateArgumentKind SBType::GetTemplateArgumentKind(uint32_t idx) {
   return eTemplateArgumentKindNull;
 }
 
+SBType SBType::FindDirectNestedType(const char *name) {
+  LLDB_INSTRUMENT_VA(this, name);
+
+  if (!IsValid())
+    return SBType();
+  return SBType(m_opaque_sp->FindDirectNestedType(name));
+}
+
 SBTypeList::SBTypeList() : m_opaque_up(new TypeListImpl()) {
   LLDB_INSTRUMENT_VA(this);
 }

lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp

@@ -2637,6 +2637,13 @@ TypeSystemClang::GetDeclContextForType(const CompilerType &type) {
   return GetDeclContextForType(ClangUtil::GetQualType(type));
 }
 
+CompilerDeclContext
+TypeSystemClang::GetCompilerDeclContextForType(const CompilerType &type) {
+  if (auto *decl_context = GetDeclContextForType(type))
+    return CreateDeclContext(decl_context);
+  return CompilerDeclContext();
+}
+
 /// Aggressively desugar the provided type, skipping past various kinds of
 /// syntactic sugar and other constructs one typically wants to ignore.
 /// The \p mask argument allows one to skip certain kinds of simplifications,

lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.h

@@ -219,6 +219,9 @@ class TypeSystemClang : public TypeSystem {
 
   static clang::DeclContext *GetDeclContextForType(const CompilerType &type);
 
+  CompilerDeclContext
+  GetCompilerDeclContextForType(const CompilerType &type) override;
+
   uint32_t GetPointerByteSize() override;
 
   clang::TranslationUnitDecl *GetTranslationUnitDecl() {

lldb/source/Symbol/Type.cpp

@@ -1040,6 +1040,23 @@ bool TypeImpl::GetDescription(lldb_private::Stream &strm,
   return true;
 }
 
+CompilerType TypeImpl::FindDirectNestedType(llvm::StringRef name) {
+  if (name.empty())
+    return CompilerType();
+  auto type_system = GetTypeSystem(/*prefer_dynamic*/ false);
+  auto *symbol_file = type_system->GetSymbolFile();
+  auto decl_context = type_system->GetCompilerDeclContextForType(m_static_type);
+  if (!decl_context.IsValid())
+    return CompilerType();
+  llvm::DenseSet<lldb_private::SymbolFile *> searched_symbol_files;
+  TypeMap search_result;
+  symbol_file->FindTypes(ConstString(name), decl_context, /*max_matches*/ 1,
+                         searched_symbol_files, search_result);
+  if (search_result.Empty())
+    return CompilerType();
+  return search_result.GetTypeAtIndex(0)->GetFullCompilerType();
+}
+
 bool TypeMemberFunctionImpl::IsValid() {
   return m_type.IsValid() && m_kind != lldb::eMemberFunctionKindUnknown;
 }

lldb/source/Symbol/TypeSystem.cpp

@@ -186,6 +186,11 @@ std::optional<llvm::json::Value> TypeSystem::ReportStatistics() {
   return std::nullopt;
 }
 
+CompilerDeclContext
+TypeSystem::GetCompilerDeclContextForType(const CompilerType &type) {
+  return CompilerDeclContext();
+}
+
 #pragma mark TypeSystemMap
 
 TypeSystemMap::TypeSystemMap() : m_mutex(), m_map() {}

lldb/test/API/python_api/type/TestTypeList.py

@@ -119,6 +119,37 @@ def test(self):
 
         self.assertEqual(task_type, task_head_pointee_type)
 
+        # Check whether we can find a directly nested type by name
+        name_type = task_type.FindDirectNestedType("name")
+        self.assertTrue(name_type)
+        self.DebugSBType(name_type)
+
+        enum_type = task_type.FindDirectNestedType("E")
+        self.assertTrue(enum_type)
+        self.DebugSBType(enum_type)
+
+        union_type = task_type.FindDirectNestedType("U")
+        self.assertTrue(union_type)
+        self.DebugSBType(union_type)
+
+        # Check that we don't find indirectly nested types
+        self.assertTrue(enum_type.size == 1)
+
+        invalid_type = task_type.FindDirectNestedType("E2")
+        self.assertFalse(invalid_type)
+
+        # Check that FindDirectNestedType handles types without DeclContext
+        # and other errorneous inputs
+        task_ptr_type = task_type.GetPointerType()
+        invalid_type = task_ptr_type.FindDirectNestedType("name")
+        self.assertFalse(invalid_type)
+
+        invalid_type = task_type.FindDirectNestedType("")
+        self.assertFalse(invalid_type)
+
+        invalid_type = task_type.FindDirectNestedType(None)
+        self.assertFalse(invalid_type)
+
         # We'll now get the child member 'id' from 'task_head'.
         id = task_head.GetChildMemberWithName("id")
         self.DebugSBValue(id)

lldb/test/API/python_api/type/main.cpp

@@ -21,7 +21,12 @@ class Task {
     } my_type_is_nameless;
     struct name {
       int x;
+      enum E : int {} e;
+      enum E2 {} e2;
     } my_type_is_named;
+    enum E : unsigned char {} e;
+    union U {
+    } u;
     Task(int i, Task *n):
         id(i),
         next(n),

llvm/docs/ReleaseNotes.rst

@@ -191,6 +191,10 @@ Changes to LLDB
 
 * Methods in SBHostOS related to threads have had their implementations
   removed. These methods will return a value indicating failure.
+* ``SBType::FindDirectNestedType`` function is added. It's useful
+  for formatters to quickly find directly nested type when it's known
+  where to search for it, avoiding more expensive global search via
+  ``SBTarget::FindFirstType``.
 
 Changes to Sanitizers
 ---------------------