[lldb][NFC] Add unit test for persistent variable lookup with ClangExpressionDeclMap

This adds a unit test for looking up persistent declarations in the scratch AST
context. Also adds the `GetPersistentDecl` hook to the ClangExpressionDeclMap
that this unit test can emulate looking up persistent variables without having
a lldb_private::Target.

lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp

@@ -734,29 +734,33 @@ void ClangExpressionDeclMap::MaybeRegisterFunctionBody(
   }
 }
 
-void ClangExpressionDeclMap::SearchPersistenDecls(NameSearchContext &context,
-                                                  const ConstString name,
-                                                  unsigned int current_id) {
-  Log *log(lldb_private::GetLogIfAllCategoriesSet(LIBLLDB_LOG_EXPRESSIONS));
+clang::NamedDecl *ClangExpressionDeclMap::GetPersistentDecl(ConstString name) {
   if (!m_parser_vars)
-    return;
+    return nullptr;
   Target *target = m_parser_vars->m_exe_ctx.GetTargetPtr();
   if (!target)
-    return;
+    return nullptr;
 
   ClangASTContext *scratch_clang_ast_context =
       ClangASTContext::GetScratch(*target);
 
   if (!scratch_clang_ast_context)
-    return;
+    return nullptr;
 
   ASTContext *scratch_ast_context = scratch_clang_ast_context->getASTContext();
 
   if (!scratch_ast_context)
-    return;
+    return nullptr;
 
-  NamedDecl *persistent_decl =
-      m_parser_vars->m_persistent_vars->GetPersistentDecl(name);
+  return m_parser_vars->m_persistent_vars->GetPersistentDecl(name);
+}
+
+void ClangExpressionDeclMap::SearchPersistenDecls(NameSearchContext &context,
+                                                  const ConstString name,
+                                                  unsigned int current_id) {
+  Log *log(lldb_private::GetLogIfAllCategoriesSet(LIBLLDB_LOG_EXPRESSIONS));
+
+  NamedDecl *persistent_decl = GetPersistentDecl(name);
 
   if (!persistent_decl)
     return;
@@ -1409,6 +1413,10 @@ void ClangExpressionDeclMap::FindExternalVisibleDecls(
     if (name.GetStringRef().startswith("$__lldb"))
       return;
 
+    // No ParserVars means we can't do register or variable lookup.
+    if (!m_parser_vars)
+      return;
+
     ExpressionVariableSP pvar_sp(
         m_parser_vars->m_persistent_vars->GetVariable(name));
 

lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.h

@@ -283,6 +283,14 @@ public:
                                 CompilerDeclContext &namespace_decl,
                                 unsigned int current_id);
 
+protected:
+  /// Retrieves the declaration with the given name from the storage of
+  /// persistent declarations.
+  ///
+  /// \return
+  ///     A persistent decl with the given name or a nullptr.
+  virtual clang::NamedDecl *GetPersistentDecl(ConstString name);
+
 private:
   ExpressionVariableList
       m_found_entities; ///< All entities that were looked up for the parser.

lldb/unittests/Expression/ClangExpressionDeclMapTest.cpp

@@ -11,12 +11,51 @@
 #include "lldb/Host/FileSystem.h"
 #include "lldb/Host/HostInfo.h"
 #include "lldb/Symbol/ClangASTContext.h"
+#include "lldb/Symbol/ClangUtil.h"
 #include "lldb/lldb-defines.h"
 #include "gtest/gtest.h"
 
 using namespace lldb_private;
 using namespace lldb;
 
+static std::unique_ptr<ClangASTContext> createAST() {
+  return std::make_unique<ClangASTContext>(HostInfo::GetTargetTriple());
+}
+
+namespace {
+struct FakeClangExpressionDeclMap : public ClangExpressionDeclMap {
+  FakeClangExpressionDeclMap(const ClangASTImporterSP &importer)
+      : ClangExpressionDeclMap(false, nullptr, lldb::TargetSP(), importer,
+                               nullptr) {
+    m_scratch_context = createAST();
+  }
+  std::unique_ptr<ClangASTContext> m_scratch_context;
+  /// Adds a persistent decl that can be found by the ClangExpressionDeclMap
+  /// via GetPersistentDecl.
+  void AddPersistentDeclForTest(clang::NamedDecl *d) {
+    // The declaration needs to have '$' prefix in its name like every
+    // persistent declaration and must be inside the scratch AST context.
+    assert(d);
+    assert(d->getName().startswith("$"));
+    assert(&d->getASTContext() == m_scratch_context->getASTContext());
+    m_persistent_decls[d->getName()] = d;
+  }
+
+protected:
+  // ClangExpressionDeclMap hooks.
+
+  clang::NamedDecl *GetPersistentDecl(ConstString name) override {
+    // ClangExpressionDeclMap wants to know if there is a persistent decl
+    // with the given name. Check the
+    return m_persistent_decls.lookup(name.GetStringRef());
+  }
+
+private:
+  /// The persistent decls in this test with their names as keys.
+  llvm::DenseMap<llvm::StringRef, clang::NamedDecl *> m_persistent_decls;
+};
+} // namespace
+
 namespace {
 struct ClangExpressionDeclMapTest : public testing::Test {
   static void SetUpTestCase() {
@@ -28,8 +67,25 @@ struct ClangExpressionDeclMapTest : public testing::Test {
     FileSystem::Terminate();
   }
 
-  std::unique_ptr<ClangASTContext> createAST() {
-    return std::make_unique<ClangASTContext>(HostInfo::GetTargetTriple());
+  /// The ClangASTImporter used during the test.
+  ClangASTImporterSP importer;
+  /// The ExpressionDeclMap for the current test case.
+  std::unique_ptr<FakeClangExpressionDeclMap> decl_map;
+
+  /// The target AST that lookup results should be imported to.
+  std::unique_ptr<ClangASTContext> target_ast;
+
+  void SetUp() override {
+    importer = std::make_shared<ClangASTImporter>();
+    decl_map = std::make_unique<FakeClangExpressionDeclMap>(importer);
+    target_ast = createAST();
+    decl_map->InstallASTContext(*target_ast, *target_ast->getFileManager());
+  }
+
+  void TearDown() override {
+    importer.reset();
+    decl_map.reset();
+    target_ast.reset();
   }
 
   clang::DeclarationName getDeclarationName(ClangASTContext &ast,
@@ -37,23 +93,54 @@ struct ClangExpressionDeclMapTest : public testing::Test {
     clang::IdentifierInfo &II = ast.getIdentifierTable()->get(name);
     return ast.getASTContext()->DeclarationNames.getIdentifier(&II);
   }
+
+  CompilerType createRecord(ClangASTContext &ast, llvm::StringRef name) {
+    CompilerType t = ast.CreateRecordType(ast.getASTContext()->getTranslationUnitDecl(),
+                                lldb::AccessType::eAccessPublic, name, 0,
+                                lldb::LanguageType::eLanguageTypeC);
+    ClangASTContext::StartTagDeclarationDefinition(t);
+    ClangASTContext::CompleteTagDeclarationDefinition(t);
+    return t;
+  }
 };
 } // namespace
 
-TEST_F(ClangExpressionDeclMapTest, TestIdentifierLookupInEmptyTU) {
-  ClangASTImporterSP importer = std::make_shared<ClangASTImporter>();
-  ClangExpressionDeclMap map(false, nullptr, lldb::TargetSP(), importer,
-                             nullptr);
-
-  std::unique_ptr<ClangASTContext> ast = createAST();
-  map.InstallASTContext(*ast, *ast->getFileManager());
+TEST_F(ClangExpressionDeclMapTest, TestUnknownIdentifierLookup) {
+  // Tests looking up an identifier that can't be found anywhere.
 
+  // Setup a NameSearchContext for 'foo'.
   llvm::SmallVector<clang::NamedDecl *, 16> decls;
-  clang::DeclarationName name = getDeclarationName(*ast, "does_no_exist");
-  const clang::DeclContext *dc = ast->GetTranslationUnitDecl();
+  clang::DeclarationName name = getDeclarationName(*target_ast, "foo");
+  const clang::DeclContext *dc = target_ast->GetTranslationUnitDecl();
+  NameSearchContext search(*decl_map, decls, name, dc);
 
-  NameSearchContext search(map, decls, name, dc);
-  map.FindExternalVisibleDecls(search);
+  decl_map->FindExternalVisibleDecls(search);
 
+  // This shouldn't exist so we should get no lookups.
   EXPECT_EQ(0U, decls.size());
 }
+
+TEST_F(ClangExpressionDeclMapTest, TestPersistentDeclLookup) {
+  // Tests looking up a persistent decl from the scratch AST context.
+
+  // Create a '$persistent_class' record and add it as a persistent variable
+  // to the scratch AST context.
+  llvm::StringRef decl_name = "$persistent_class";
+  CompilerType persistent_type =
+      createRecord(*decl_map->m_scratch_context, decl_name);
+  decl_map->AddPersistentDeclForTest(ClangUtil::GetAsTagDecl(persistent_type));
+
+  // Setup a NameSearchContext for $persistent_class;
+  llvm::SmallVector<clang::NamedDecl *, 16> decls;
+  clang::DeclarationName name = getDeclarationName(*target_ast, decl_name);
+  const clang::DeclContext *dc = target_ast->GetTranslationUnitDecl();
+  NameSearchContext search(*decl_map, decls, name, dc);
+
+  // Search and check that we found $persistent_class.
+  decl_map->FindExternalVisibleDecls(search);
+  EXPECT_EQ(1U, decls.size());
+  EXPECT_EQ(decl_name, decls.front()->getQualifiedNameAsString());
+  auto *record = llvm::cast<clang::RecordDecl>(decls.front());
+  // The class was minimally imported from the scratch AST context.
+  EXPECT_TRUE(record->hasExternalLexicalStorage());
+}