[LLDB][NativePDB] Implement FindNamespace (#151950)

`FindNamespace` was not implemented for `SymbolFileNativePDB`. Without
it, it wasn't possible to lookup items through namespaces when
evaluating expressions.

This is mostly the same as in
[SymbolFilePDB](https://github.com/llvm/llvm-project/blob/f1eb869bae2ab86726ee3a5a5c7980d5b2acbd5d/lldb/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp#L1664-L1696)
as well as
[PDBAstParser](https://github.com/llvm/llvm-project/blob/f1eb869bae2ab86726ee3a5a5c7980d5b2acbd5d/lldb/source/Plugins/SymbolFile/PDB/PDBASTParser.cpp#L1126-L1150):
The AST parser/builder saves the created namespaces in a map to lookup
when a namespace is requested.

This is working towards making
[Shell/SymbolFile/PDB/expressions.test](https://github.com/llvm/llvm-project/blob/f1eb869bae2ab86726ee3a5a5c7980d5b2acbd5d/lldb/test/Shell/SymbolFile/PDB/expressions.test)
pass with the native PDB plugin.

Author: Nerixyz

lldb/source/Plugins/SymbolFile/NativePDB/PdbAstBuilder.cpp

@@ -644,9 +644,12 @@ clang::Decl *PdbAstBuilder::TryGetDecl(PdbSymUid uid) const {
 clang::NamespaceDecl *
 PdbAstBuilder::GetOrCreateNamespaceDecl(const char *name,
                                         clang::DeclContext &context) {
-  return m_clang.GetUniqueNamespaceDeclaration(
+  clang::NamespaceDecl *ns = m_clang.GetUniqueNamespaceDeclaration(
       IsAnonymousNamespaceName(name) ? nullptr : name, &context,
       OptionalClangModuleID());
+  m_known_namespaces.insert(ns);
+  m_parent_to_namespaces[&context].insert(ns);
+  return ns;
 }
 
 clang::BlockDecl *
@@ -1452,3 +1455,30 @@ PdbAstBuilder::FromCompilerDeclContext(CompilerDeclContext context) {
 void PdbAstBuilder::Dump(Stream &stream, llvm::StringRef filter) {
   m_clang.Dump(stream.AsRawOstream(), filter);
 }
+
+clang::NamespaceDecl *
+PdbAstBuilder::FindNamespaceDecl(const clang::DeclContext *parent,
+                                 llvm::StringRef name) {
+  NamespaceSet *set;
+  if (parent) {
+    auto it = m_parent_to_namespaces.find(parent);
+    if (it == m_parent_to_namespaces.end())
+      return nullptr;
+
+    set = &it->second;
+  } else {
+    // In this case, search through all known namespaces
+    set = &m_known_namespaces;
+  }
+  assert(set);
+
+  for (clang::NamespaceDecl *namespace_decl : *set)
+    if (namespace_decl->getName() == name)
+      return namespace_decl;
+
+  for (clang::NamespaceDecl *namespace_decl : *set)
+    if (namespace_decl->isAnonymousNamespace())
+      return FindNamespaceDecl(namespace_decl, name);
+
+  return nullptr;
+}

lldb/source/Plugins/SymbolFile/NativePDB/PdbAstBuilder.h

@@ -89,6 +89,9 @@ class PdbAstBuilder {
 
   void Dump(Stream &stream, llvm::StringRef filter);
 
+  clang::NamespaceDecl *FindNamespaceDecl(const clang::DeclContext *parent,
+                                          llvm::StringRef name);
+
 private:
   clang::Decl *TryGetDecl(PdbSymUid uid) const;
 
@@ -150,7 +153,15 @@ class PdbAstBuilder {
   llvm::DenseMap<lldb::opaque_compiler_type_t,
                  llvm::SmallSet<std::pair<llvm::StringRef, CompilerType>, 8>>
       m_cxx_record_map;
-  llvm::DenseSet<clang::NamespaceDecl *> m_parsed_namespaces;
+
+  using NamespaceSet = llvm::DenseSet<clang::NamespaceDecl *>;
+
+  // These namespaces are fully parsed
+  NamespaceSet m_parsed_namespaces;
+
+  // We know about these namespaces, but they might not be completely parsed yet
+  NamespaceSet m_known_namespaces;
+  llvm::DenseMap<clang::DeclContext *, NamespaceSet> m_parent_to_namespaces;
 };
 
 } // namespace npdb

lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp

@@ -2168,9 +2168,36 @@ void SymbolFileNativePDB::GetTypes(lldb_private::SymbolContextScope *sc_scope,
                                    TypeClass type_mask,
                                    lldb_private::TypeList &type_list) {}
 
-CompilerDeclContext SymbolFileNativePDB::FindNamespace(
-    ConstString name, const CompilerDeclContext &parent_decl_ctx, bool) {
-  return {};
+CompilerDeclContext
+SymbolFileNativePDB::FindNamespace(ConstString name,
+                                   const CompilerDeclContext &parent_decl_ctx,
+                                   bool /* only_root_namespaces */) {
+  std::lock_guard<std::recursive_mutex> guard(GetModuleMutex());
+  auto ts_or_err = GetTypeSystemForLanguage(lldb::eLanguageTypeC_plus_plus);
+  if (auto err = ts_or_err.takeError())
+    return {};
+  auto ts = *ts_or_err;
+  if (!ts)
+    return {};
+  auto *clang = llvm::dyn_cast_or_null<TypeSystemClang>(ts.get());
+  if (!clang)
+    return {};
+
+  PdbAstBuilder *ast_builder = clang->GetNativePDBParser();
+  if (!ast_builder)
+    return {};
+
+  clang::DeclContext *decl_context = nullptr;
+  if (parent_decl_ctx)
+    decl_context = static_cast<clang::DeclContext *>(
+        parent_decl_ctx.GetOpaqueDeclContext());
+
+  auto *namespace_decl =
+      ast_builder->FindNamespaceDecl(decl_context, name.GetStringRef());
+  if (!namespace_decl)
+    return CompilerDeclContext();
+
+  return clang->CreateDeclContext(namespace_decl);
 }
 
 llvm::Expected<lldb::TypeSystemSP>

lldb/test/Shell/SymbolFile/NativePDB/namespace-access.test

@@ -77,8 +77,17 @@ type lookup Outer::Inner2::S
 type lookup Outer::A
 type lookup A
 type lookup ::A
+# Test that Clang can find the namespaces as well
 expr sizeof(S)
+expr sizeof(::S)
+expr sizeof(Outer::S)
+expr sizeof(Outer::Inner1::S)
+expr sizeof(Inner1::S)
+expr sizeof(Outer::Inner1::Inner2::S)
+expr sizeof(Outer::Inner2::S)
+expr sizeof(Outer::A)
 expr sizeof(A)
+expr sizeof(::A)
 
 quit
 
@@ -131,5 +140,21 @@ quit
 # CHECK-NEXT: }
 # CHECK-NEXT: (lldb) expr sizeof(S) 
 # CHECK-NEXT: (__size_t) $0 = 1
+# CHECK-NEXT: (lldb) expr sizeof(::S)
+# CHECK-NEXT: (__size_t) $1 = 1
+# CHECK-NEXT: (lldb) expr sizeof(Outer::S)
+# CHECK-NEXT: (__size_t) $2 = 2
+# CHECK-NEXT: (lldb) expr sizeof(Outer::Inner1::S)
+# CHECK-NEXT: (__size_t) $3 = 3
+# CHECK-NEXT: (lldb) expr sizeof(Inner1::S)
+# CHECK-NEXT: (__size_t) $4 = 3
+# CHECK-NEXT: (lldb) expr sizeof(Outer::Inner1::Inner2::S)
+# CHECK-NEXT: (__size_t) $5 = 4
+# CHECK-NEXT: (lldb) expr sizeof(Outer::Inner2::S)
+# CHECK-NEXT: (__size_t) $6 = 5
+# CHECK-NEXT: (lldb) expr sizeof(Outer::A)
+# CHECK-NEXT: (__size_t) $7 = 6
 # CHECK-NEXT: (lldb) expr sizeof(A)
-# CHECK-NEXT: (__size_t) $1 = 7
+# CHECK-NEXT: (__size_t) $8 = 7
+# CHECK-NEXT: (lldb) expr sizeof(::A)
+# CHECK-NEXT: (__size_t) $9 = 7