[lldb] Add support for using variables with C++ keywords names in non-C++ expressions

[teemperor]

Summary

LLDB is currently always activating C++ when parsing expressions as LLDB itself is using C++ features
when creating the final AST that will be codegen'd (specifically, references to variables, namespaces
and using declarations are used).

This is causing problems for users that have variables in non-C++ programs (e.g. plain C or Objective-C)
that have names which are keywords in C++. Expressions referencing those variables fail to parse
as LLDB's Clang parser thinks those identifiers are C++ keywords and not identifiers that may belong
to a declaration.

We can't just disable C++ in the expression parser for those situations as replacing the functionality of the
injected C++ code isn't trivial. So this patch is just disabling most keywords that are exclusive to C++ in
LLDB's Clang parser when we are in a non-C++ expression. There are a few keywords we can't disable for now:

• using as that's currently used in some situations to inject variables into the expression function.
• __null as that's used by LLDB to define NULL/Nil/nil.

Getting rid of these last two keywords is possible but is a large enough change that this will be handled in
follow up patches.

Note that this only changes the keyword status of those tokens but this patch does not remove any C++
functionality from the expression parser. The type system still follows C++ rules and so does the rest
of the expression parser.

There is another small change that gives the hardcoded macro definitions in LLDB a higher precedence
than the macros imported from the Objective-C modules. The reason for this is that the Objective-C
modules in LLDB are actually parsed in Objective-C++ mode and they end up providing the C++ definitions
of certain system macros (like NULL being defined as nullptr). So we have to move the LLDB definition
forward and surround the definition from the module with an #ifdef to make sure that we use the correct
LLDB definition that doesn't reference C++ keywords. Or to give an example, this is how the expression
source code changes:

Before:

#define NULL (nullptr) // injected module definition
#ifndef NULL
#define NULL (__null) // hardcoded LLDB definition
#endif

After:

#ifndef NULL
#define NULL (__null) // hardcoded LLDB definition
#endif
#ifndef NULL
#define NULL (nullptr) // injected module definition
#endif

Fixes rdar://10356912

[teemperor]

• Fixed a typo.
• Added tests for using a struct with a keyword name in a C++ expression.

[shafik]

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

312

I was looking at isCPlusPlusKeyword() and C++14 nor C++17 added any keywords. If note that function does use either of those.

I was also wondering, b/c it was not obvious after looking at this for a bit, if shared keywords like 'register' (although that is deprecated) also get clobbered.

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

354

Is change actually tested? I don't see it being tested but maybe I am missing it.

It also feels like it should be a separate PR.

[labath]

I don't really have much to say on this. At first I though this was going to be very hacky, but it actually looks fairly elegant. It may still make sense to check whether doing this is reasonable with some clang folks, if you haven't already.

lldb/test/API/lang/c/cpp_keyword_identifiers/TestCppKeywordsAsCIdentifiers.py

10

What's up with this?

lldb/test/API/lang/objcxx/cpp_keywords_enabled/TestObjCppKeywordsEnabled.py

11

Should maybe this have @skipUnlessDarwin instead?

[teemperor]

Sorry, this was still on my "Waiting on review" queue as no one pressed the "changes requested" button.

Changes for this revision:

• Moved test decorator to right test.
• Removed C++14/17 from keyword check.
• Refactored the NULL workaround to make it easier to follow (and also more generic).

[teemperor]

• Added a explicit check for the module related change.

[teemperor]

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

354

I described in the review description what this was for, but I change the code now and replaced it with a more generic "put #ifdefs around our defines" approach (which should hopefully be less cryptic and also general seems like a good idea).

The change is tested by the existing LLDB tests that use macros from Clang modules.

lldb/test/API/lang/c/cpp_keyword_identifiers/TestCppKeywordsAsCIdentifiers.py

10

That's me editing the wrong file :)

lldb/test/API/lang/objcxx/cpp_keywords_enabled/TestObjCppKeywordsEnabled.py

11

Jepp, thanks!

[shafik]

LGTM

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

static void SetupModuleHeaderPaths(CompilerInstance *compiler,
   search_opts.ModuleCachePath = std::string(module_cache.str());
   LLDB_LOG(log, "Using module cache path: {0}", module_cache.c_str());
 
   search_opts.ResourceDir = GetClangResourceDir().GetPath();
 
   search_opts.ImplicitModuleMaps = true;
 }
 
+/// Iff the given identifier is a C++ keyword, remove it from the
+/// identifier table (i.e., make the token a normal identifier).
+static void RemoveCppKeyword(IdentifierTable &idents, llvm::StringRef token) {
+  // FIXME: 'using' is used by LLDB for local variables, so we can't remove
+  // this keyword without breaking this functionality.
+  if (token == "using")
+    return;
+  // GCC's '__null' is used by LLDB to define NULL/Nil/nil.
+  if (token == "__null")
+    return;
+
+  LangOptions cpp_lang_opts;
+  cpp_lang_opts.CPlusPlus = true;
+  cpp_lang_opts.CPlusPlus11 = true;
+  cpp_lang_opts.CPlusPlus14 = true;
+  cpp_lang_opts.CPlusPlus17 = true;
+  cpp_lang_opts.CPlusPlus20 = true;
+
+  clang::IdentifierInfo &ii = idents.get(token);
+  // If the identifier is not a keyword in any C++ standard then there is
+  // nothing to do.
+  if (!ii.isCPlusPlusKeyword(cpp_lang_opts))
+    return;
+  // If the token is already an identifier, then there is nothing to do.
+  if (ii.getTokenID() == clang::tok::identifier)
+    return;
+  // Otherwise the token is a C++ keyword, so turn it back into a normal
+  // identifier.
+  ii.revertTokenIDToIdentifier();
+}
+
+/// Remove all C++ keywords from the given identifier table.
+static void RemoveAllCppKeywords(IdentifierTable &idents) {
+#define KEYWORD(NAME, FLAGS) RemoveCppKeyword(idents, llvm::StringRef(#NAME));
+#include "clang/Basic/TokenKinds.def"
+}
+
 //===----------------------------------------------------------------------===//
 // Implementation of ClangExpressionParser
 //===----------------------------------------------------------------------===//
 
 ClangExpressionParser::ClangExpressionParser(
     ExecutionContextScope *exe_scope, Expression &expr,
     bool generate_debug_info, std::vector<std::string> include_directories,
     std::string filename)
ClangExpressionParser::ClangExpressionParser(
   m_compiler->getDiagnostics().setClient(diag_mgr);
 
   // 7. Set up the source management objects inside the compiler
   m_compiler->createFileManager();
   if (!m_compiler->hasSourceManager())
     m_compiler->createSourceManager(m_compiler->getFileManager());
   m_compiler->createPreprocessor(TU_Complete);
 
+  switch (language) {
+  case lldb::eLanguageTypeC:
+  case lldb::eLanguageTypeC89:
+  case lldb::eLanguageTypeC99:
+  case lldb::eLanguageTypeC11:
+  case lldb::eLanguageTypeObjC:
+    // This is not a C++ expression but we enabled C++ as explained above.
+    // Remove all C++ keywords from the PP so that the user can still use
+    // variables that have C++ keywords as names (e.g. 'int template;').
+    RemoveAllCppKeywords(m_compiler->getPreprocessor().getIdentifierTable());
+    break;
+  default:
+    break;
+  }
+
   if (ClangModulesDeclVendor *decl_vendor =
           target_sp->GetClangModulesDeclVendor()) {
     if (auto *clang_persistent_vars = llvm::cast<ClangPersistentVariables>(
             target_sp->GetPersistentExpressionStateForLanguage(
                 lldb::eLanguageTypeC))) {
       std::unique_ptr<PPCallbacks> pp_callbacks(
           new LLDBPreprocessorCallbacks(*decl_vendor, *clang_persistent_vars,
                                         m_compiler->getSourceManager()));

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

void ClangExpressionSourceCode::AddLocalVariableDecls(
   }
 }
 
 bool ClangExpressionSourceCode::GetText(
     std::string &text, ExecutionContext &exe_ctx, bool add_locals,
     bool force_add_all_locals, llvm::ArrayRef<std::string> modules) const {
   const char *target_specific_defines = "typedef signed char BOOL;\n";
   std::string module_macros;
+  llvm::raw_string_ostream module_macros_stream(module_macros);
 
   Target *target = exe_ctx.GetTargetPtr();
   if (target) {
     if (target->GetArchitecture().GetMachine() == llvm::Triple::aarch64 ||
         target->GetArchitecture().GetMachine() == llvm::Triple::aarch64_32) {
       target_specific_defines = "typedef bool BOOL;\n";
     }
     if (target->GetArchitecture().GetMachine() == llvm::Triple::x86_64) {
if (decl_vendor && persistent_vars) {
                   *sc.comp_unit, modules_for_macros, error_stream);
             }
           }
         }
       }
 
       decl_vendor->ForEachMacro(
           modules_for_macros,
-          [&module_macros](const std::string &expansion) -> bool {
-            module_macros.append(expansion);
-            module_macros.append("\n");
+          [&module_macros_stream](llvm::StringRef token,
+                                  llvm::StringRef expansion) -> bool {
+            // LLDB provides these defines already, so don't expand those macros
+            // in case they are defined in a way that doesn't fit to the way
+            // the Clang parser is defined (e.g., 'NULL' being defined as
+            // 'nullptr' but we're currently parsing a C expression).
+            if (token == "NULL" || token == "nil" || token == "Nil")
+              return false;
+            module_macros_stream << expansion << "\n";
             return false;
           });
     }
   }
 
   StreamString debug_macros_stream;
   StreamString lldb_local_var_decls;
   if (StackFrame *frame = exe_ctx.GetFramePtr()) {

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

public:
   /// that are already imported.
   ///
   /// \param[in] modules
   ///     The unique IDs for all modules to query.  Later modules have higher
   ///     priority, just as if you @imported them in that order.  This matters
   ///     if module A #defines a macro and module B #undefs it.
   ///
   /// \param[in] handler
-  ///     A function to call with the text of each #define (including the
-  ///     #define directive).  #undef directives are not included; we simply
-  ///     elide any corresponding #define.  If this function returns true,
-  ///     we stop the iteration immediately.
-  virtual void
-  ForEachMacro(const ModuleVector &modules,
-               std::function<bool(const std::string &)> handler) = 0;
+  ///     A function to call with the identifier of this macro and the text of
+  ///     each #define (including the #define directive). #undef directives are
+  ///     not included; we simply elide any corresponding #define. If this
+  ///     function returns true, we stop the iteration immediately.
+  virtual void ForEachMacro(
+      const ModuleVector &modules,
+      std::function<bool(llvm::StringRef, llvm::StringRef)> handler) = 0;
 
   /// Query whether Clang supports modules for a particular language.
   /// LLDB uses this to decide whether to try to find the modules loaded
   /// by a given compile unit.
   ///
   /// \param[in] language
   ///     The language to query for.
   ///
   /// \return
   ///     True if Clang has modules for the given language.
   static bool LanguageSupportsClangModules(lldb::LanguageType language);
 };
 
 } // namespace lldb_private
 
 #endif // LLDB_SOURCE_PLUGINS_EXPRESSIONPARSER_CLANG_CLANGMODULESDECLVENDOR_H

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

bool AddModule(const SourceModule &module, ModuleVector *exported_modules,
                  Stream &error_stream) override;
 
   bool AddModulesForCompileUnit(CompileUnit &cu, ModuleVector &exported_modules,
                                 Stream &error_stream) override;
 
   uint32_t FindDecls(ConstString name, bool append, uint32_t max_matches,
                      std::vector<CompilerDecl> &decls) override;
 
-  void ForEachMacro(const ModuleVector &modules,
-                    std::function<bool(const std::string &)> handler) override;
+  void ForEachMacro(
+      const ModuleVector &modules,
+      std::function<bool(llvm::StringRef, llvm::StringRef)> handler) override;
+
 private:
   void
   ReportModuleExportsHelper(std::set<ClangModulesDeclVendor::ModuleID> &exports,
                             clang::Module *module);
 
   void ReportModuleExports(ModuleVector &exports, clang::Module *module);
 
   clang::ModuleLoadResult DoGetModule(clang::ModuleIdPath path,
for (clang::NamedDecl *named_decl : lookup_result) {
     ++num_matches;
   }
 
   return num_matches;
 }
 
 void ClangModulesDeclVendorImpl::ForEachMacro(
     const ClangModulesDeclVendor::ModuleVector &modules,
-    std::function<bool(const std::string &)> handler) {
+    std::function<bool(llvm::StringRef, llvm::StringRef)> handler) {
   if (!m_enabled) {
     return;
   }
 
   typedef std::map<ModuleID, ssize_t> ModulePriorityMap;
   ModulePriorityMap module_priorities;
 
   ssize_t priority = 0;
for (clang::ModuleMacro *module_macro :
           macro_info = module_macro->getMacroInfo();
           found_priority = pi->second;
         }
       }
     }
 
     if (macro_info) {
       std::string macro_expansion = "#define ";
-      macro_expansion.append(mi->first->getName().str());
+      llvm::StringRef macro_identifier = mi->first->getName();
+      macro_expansion.append(macro_identifier.str());
 
       {
         if (macro_info->isFunctionLike()) {
           macro_expansion.append("(");
 
           bool first_arg = true;
 
           for (auto pi = macro_info->param_begin(),
if (macro_info) {
               break;
             default:
               macro_expansion.append(ti->getName());
               break;
             }
           }
         }
 
-        if (handler(macro_expansion)) {
+        if (handler(macro_identifier, macro_expansion)) {
           return;
         }
       }
     }
   }
 }
 
 clang::ModuleLoadResult

lldb/test/API/lang/c/cpp_keyword_identifiers/Makefile

+C_SOURCES := main.c
+
+include Makefile.rules

lldb/test/API/lang/c/cpp_keyword_identifiers/TestCppKeywordsAsCIdentifiers.py

+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+class TestCase(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    @skipUnlessDarwin
+    @no_debug_info_test
+    def test(self):
+        self.build()
+        lldbutil.run_to_source_breakpoint(self, "// break here", lldb.SBFileSpec("main.c"))
+
+        # Test several variables with C++ keyword names and make sure they
+        # work as intended in the expression parser.
+        self.expect_expr("alignas", result_type="int", result_value="1")
+        self.expect_expr("alignof", result_type="int", result_value="1")
+        self.expect_expr("and", result_type="int", result_value="1")
+        self.expect_expr("and_eq", result_type="int", result_value="1")
+        self.expect_expr("atomic_cancel", result_type="int", result_value="1")
+        self.expect_expr("atomic_commit", result_type="int", result_value="1")
+        self.expect_expr("atomic_noexcept", result_type="int", result_value="1")
+        self.expect_expr("bitand", result_type="int", result_value="1")
+        self.expect_expr("bitor", result_type="int", result_value="1")
+        self.expect_expr("catch", result_type="int", result_value="1")
+        self.expect_expr("char8_t", result_type="int", result_value="1")
+        self.expect_expr("char16_t", result_type="int", result_value="1")
+        self.expect_expr("char32_t", result_type="int", result_value="1")
+        self.expect_expr("class", result_type="int", result_value="1")
+        self.expect_expr("compl", result_type="int", result_value="1")
+        self.expect_expr("concept", result_type="int", result_value="1")
+        self.expect_expr("consteval", result_type="int", result_value="1")
+        self.expect_expr("constexpr", result_type="int", result_value="1")
+        self.expect_expr("constinit", result_type="int", result_value="1")
+        self.expect_expr("const_cast", result_type="int", result_value="1")
+        self.expect_expr("co_await", result_type="int", result_value="1")
+        self.expect_expr("co_return", result_type="int", result_value="1")
+        self.expect_expr("co_yield", result_type="int", result_value="1")
+        self.expect_expr("decltype", result_type="int", result_value="1")
+        self.expect_expr("delete", result_type="int", result_value="1")
+        self.expect_expr("dynamic_cast", result_type="int", result_value="1")
+        self.expect_expr("explicit", result_type="int", result_value="1")
+        self.expect_expr("export", result_type="int", result_value="1")
+        self.expect_expr("friend", result_type="int", result_value="1")
+        self.expect_expr("mutable", result_type="int", result_value="1")
+        self.expect_expr("namespace", result_type="int", result_value="1")
+        self.expect_expr("new", result_type="int", result_value="1")
+        self.expect_expr("noexcept", result_type="int", result_value="1")
+        self.expect_expr("not", result_type="int", result_value="1")
+        self.expect_expr("not_eq", result_type="int", result_value="1")
+        self.expect_expr("operator", result_type="int", result_value="1")
+        self.expect_expr("or", result_type="int", result_value="1")
+        self.expect_expr("or_eq", result_type="int", result_value="1")
+        self.expect_expr("private", result_type="int", result_value="1")
+        self.expect_expr("protected", result_type="int", result_value="1")
+        self.expect_expr("public", result_type="int", result_value="1")
+        self.expect_expr("reflexpr", result_type="int", result_value="1")
+        self.expect_expr("reinterpret_cast", result_type="int", result_value="1")
+        self.expect_expr("requires", result_type="int", result_value="1")
+        self.expect_expr("static_assert", result_type="int", result_value="1")
+        self.expect_expr("static_cast", result_type="int", result_value="1")
+        self.expect_expr("synchronized", result_type="int", result_value="1")
+        self.expect_expr("template", result_type="int", result_value="1")
+        self.expect_expr("this", result_type="int", result_value="1")
+        self.expect_expr("thread_local", result_type="int", result_value="1")
+        self.expect_expr("throw", result_type="int", result_value="1")
+        self.expect_expr("try", result_type="int", result_value="1")
+        self.expect_expr("typeid", result_type="int", result_value="1")
+        self.expect_expr("typename", result_type="int", result_value="1")
+        self.expect_expr("virtual", result_type="int", result_value="1")
+        self.expect_expr("xor", result_type="int", result_value="1")
+        self.expect_expr("xor_eq", result_type="int", result_value="1")
+
+        # Some keywords are not available in LLDB as their language feature
+        # is enabled by default.
+
+        # 'using' is used by LLDB for local variables.
+        self.expect("expr using", error=True, substrs=["expected unqualified-id"])
+
+        # 'wchar_t' supported is enabled in LLDB.
+        self.expect("expr wchar_t", error=True, substrs=["expected unqualified-id"])
+
+        # LLDB enables 'bool' support by default.
+        self.expect("expr bool", error=True, substrs=["expected unqualified-id"])
+        self.expect("expr false", error=True, substrs=["expected unqualified-id"])
+        self.expect("expr true", error=True, substrs=["expected unqualified-id"])

lldb/test/API/lang/c/cpp_keyword_identifiers/main.c

+int main() {
+  // Disable clang-format as it gets confused by the keyword identifiers.
+  // clang-format off
+  int alignas = 1;
+  int alignof = 1;
+  int and = 1;
+  int and_eq = 1;
+  int atomic_cancel = 1;
+  int atomic_commit = 1;
+  int atomic_noexcept = 1;
+  int bitand = 1;
+  int bitor = 1;
+  int bool = 1;
+  int catch = 1;
+  int char8_t = 1;
+  int char16_t = 1;
+  int char32_t = 1;
+  int class = 1;
+  int compl = 1;
+  int concept = 1;
+  int consteval = 1;
+  int constexpr = 1;
+  int constinit = 1;
+  int const_cast = 1;
+  int co_await = 1;
+  int co_return = 1;
+  int co_yield = 1;
+  int decltype = 1;
+  int delete = 1;
+  int dynamic_cast = 1;
+  int explicit = 1;
+  int export = 1;
+  int false = 1;
+  int friend = 1;
+  int mutable = 1;
+  int namespace = 1;
+  int new = 1;
+  int noexcept = 1;
+  int not = 1;
+  int not_eq = 1;
+  int operator= 1;
+  int or = 1;
+  int or_eq = 1;
+  int private = 1;
+  int protected = 1;
+  int public = 1;
+  int reflexpr = 1;
+  int reinterpret_cast = 1;
+  int requires = 1;
+  int static_assert = 1;
+  int static_cast = 1;
+  int synchronized = 1;
+  int template = 1;
+  int this = 1;
+  int thread_local = 1;
+  int throw = 1;
+  int true = 1;
+  int try = 1;
+  int typeid = 1;
+  int typename = 1;
+  int using = 1;
+  int virtual = 1;
+  int wchar_t = 1;
+  int xor = 1;
+  int xor_eq = 1;
+  // clang-format on
+  return 0; // break here
+}

lldb/test/API/lang/cpp/keywords_enabled/TestCppKeywordsEnabled.py

+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class TestCase(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    @no_debug_info_test
+    def test_keyword(self):
+      # Make sure that C++ keywords work in the expression parser.
+      self.expect("expr -l c++ -- constexpr int i = 3 + 3; i", substrs=["= 6"])

lldb/test/API/lang/cpp/struct_with_keyword_name/Makefile

+C_SOURCES := main.c
+
+include Makefile.rules

lldb/test/API/lang/cpp/struct_with_keyword_name/TestStructWithKeywordName.py

+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+class TestCase(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    @no_debug_info_test
+    def test(self):
+        self.build()
+        lldbutil.run_to_source_breakpoint(self, "// break here", lldb.SBFileSpec("main.c"))
+
+        # First run this in C which should work.
+        self.expect_expr("constexpr.class", result_type="int", result_value="3")
+
+        # Now try running this in a language that explicitly enables C++.
+        # This isn't expected to work, but at least it shouldn't crash LLDB.
+        self.expect("expr -l c++ -- constexpr.class", error=True, substrs=["expected unqualified-id"])
+        self.expect("expr -l objective-c++ -- constexpr.class", error=True, substrs=["expected unqualified-id"])

lldb/test/API/lang/cpp/struct_with_keyword_name/main.c

+struct class {
+  int class;
+};
+
+int main() {
+  struct class constexpr;
+  constexpr.class = 3;
+  return constexpr.class; // break here
+}

lldb/test/API/lang/objc/cpp_keyword_identifiers/Makefile

+OBJC_SOURCES := main.m
+
+include Makefile.rules

lldb/test/API/lang/objc/cpp_keyword_identifiers/TestCppKeywordsAsObjCIdentifiers.py

+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+class TestCase(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    @skipUnlessDarwin
+    @no_debug_info_test
+    def test(self):
+        self.build()
+        lldbutil.run_to_source_breakpoint(self, "// break here", lldb.SBFileSpec("main.m"))
+
+        # Test several variables with C++ keyword names and make sure they
+        # work as intended in the expression parser.
+        self.expect_expr("alignas", result_type="int", result_value="1")
+        self.expect_expr("alignof", result_type="int", result_value="1")
+        self.expect_expr("and", result_type="int", result_value="1")
+        self.expect_expr("and_eq", result_type="int", result_value="1")
+        self.expect_expr("atomic_cancel", result_type="int", result_value="1")
+        self.expect_expr("atomic_commit", result_type="int", result_value="1")
+        self.expect_expr("atomic_noexcept", result_type="int", result_value="1")
+        self.expect_expr("bitand", result_type="int", result_value="1")
+        self.expect_expr("bitor", result_type="int", result_value="1")
+        self.expect_expr("catch", result_type="int", result_value="1")
+        self.expect_expr("char8_t", result_type="int", result_value="1")
+        self.expect_expr("char16_t", result_type="int", result_value="1")
+        self.expect_expr("char32_t", result_type="int", result_value="1")
+        self.expect_expr("class", result_type="int", result_value="1")
+        self.expect_expr("compl", result_type="int", result_value="1")
+        self.expect_expr("concept", result_type="int", result_value="1")
+        self.expect_expr("consteval", result_type="int", result_value="1")
+        self.expect_expr("constexpr", result_type="int", result_value="1")
+        self.expect_expr("constinit", result_type="int", result_value="1")
+        self.expect_expr("const_cast", result_type="int", result_value="1")
+        self.expect_expr("co_await", result_type="int", result_value="1")
+        self.expect_expr("co_return", result_type="int", result_value="1")
+        self.expect_expr("co_yield", result_type="int", result_value="1")
+        self.expect_expr("decltype", result_type="int", result_value="1")
+        self.expect_expr("delete", result_type="int", result_value="1")
+        self.expect_expr("dynamic_cast", result_type="int", result_value="1")
+        self.expect_expr("explicit", result_type="int", result_value="1")
+        self.expect_expr("export", result_type="int", result_value="1")
+        self.expect_expr("friend", result_type="int", result_value="1")
+        self.expect_expr("mutable", result_type="int", result_value="1")
+        self.expect_expr("namespace", result_type="int", result_value="1")
+        self.expect_expr("new", result_type="int", result_value="1")
+        self.expect_expr("noexcept", result_type="int", result_value="1")
+        self.expect_expr("not", result_type="int", result_value="1")
+        self.expect_expr("not_eq", result_type="int", result_value="1")
+        self.expect_expr("operator", result_type="int", result_value="1")
+        self.expect_expr("or", result_type="int", result_value="1")
+        self.expect_expr("or_eq", result_type="int", result_value="1")
+        self.expect_expr("private", result_type="int", result_value="1")
+        self.expect_expr("protected", result_type="int", result_value="1")
+        self.expect_expr("public", result_type="int", result_value="1")
+        self.expect_expr("reflexpr", result_type="int", result_value="1")
+        self.expect_expr("reinterpret_cast", result_type="int", result_value="1")
+        self.expect_expr("requires", result_type="int", result_value="1")
+        self.expect_expr("static_assert", result_type="int", result_value="1")
+        self.expect_expr("static_cast", result_type="int", result_value="1")
+        self.expect_expr("synchronized", result_type="int", result_value="1")
+        self.expect_expr("template", result_type="int", result_value="1")
+        self.expect_expr("this", result_type="int", result_value="1")
+        self.expect_expr("thread_local", result_type="int", result_value="1")
+        self.expect_expr("throw", result_type="int", result_value="1")
+        self.expect_expr("try", result_type="int", result_value="1")
+        self.expect_expr("typeid", result_type="int", result_value="1")
+        self.expect_expr("typename", result_type="int", result_value="1")
+        self.expect_expr("virtual", result_type="int", result_value="1")
+        self.expect_expr("xor", result_type="int", result_value="1")
+        self.expect_expr("xor_eq", result_type="int", result_value="1")
+
+
+        # Some keywords are not available in LLDB as their language feature
+        # is enabled by default.
+
+        # 'using' is used by LLDB for local variables.
+        self.expect("expr using", error=True, substrs=["expected unqualified-id"])
+
+        # 'wchar_t' supported is enabled in LLDB.
+        self.expect("expr wchar_t", error=True, substrs=["expected unqualified-id"])
+
+        # LLDB enables 'bool' support by default.
+        self.expect("expr bool", error=True, substrs=["expected unqualified-id"])
+        self.expect("expr false", error=True, substrs=["expected unqualified-id"])
+        self.expect("expr true", error=True, substrs=["expected unqualified-id"])

lldb/test/API/lang/objc/cpp_keyword_identifiers/main.m

+int main() {
+  // Disable clang-format as it gets confused by the keyword identifiers.
+  // clang-format off
+  int alignas = 1;
+  int alignof = 1;
+  int and = 1;
+  int and_eq = 1;
+  int atomic_cancel = 1;
+  int atomic_commit = 1;
+  int atomic_noexcept = 1;
+  int bitand = 1;
+  int bitor = 1;
+  int bool = 1;
+  int catch = 1;
+  int char8_t = 1;
+  int char16_t = 1;
+  int char32_t = 1;
+  int class = 1;
+  int compl = 1;
+  int concept = 1;
+  int consteval = 1;
+  int constexpr = 1;
+  int constinit = 1;
+  int const_cast = 1;
+  int co_await = 1;
+  int co_return = 1;
+  int co_yield = 1;
+  int decltype = 1;
+  int delete = 1;
+  int dynamic_cast = 1;
+  int explicit = 1;
+  int export = 1;
+  int false = 1;
+  int friend = 1;
+  int mutable = 1;
+  int namespace = 1;
+  int new = 1;
+  int noexcept = 1;
+  int not = 1;
+  int not_eq = 1;
+  int operator= 1;
+  int or = 1;
+  int or_eq = 1;
+  int private = 1;
+  int protected = 1;
+  int public = 1;
+  int reflexpr = 1;
+  int reinterpret_cast = 1;
+  int requires = 1;
+  int static_assert = 1;
+  int static_cast = 1;
+  int synchronized = 1;
+  int template = 1;
+  int this = 1;
+  int thread_local = 1;
+  int throw = 1;
+  int true = 1;
+  int try = 1;
+  int typeid = 1;
+  int typename = 1;
+  int using = 1;
+  int virtual = 1;
+  int wchar_t = 1;
+  int xor = 1;
+  int xor_eq = 1;
+  // clang-format on
+  return 0; // break here
+}

lldb/test/API/lang/objcxx/cpp_keywords_enabled/TestObjCppKeywordsEnabled.py

+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class TestCase(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    @no_debug_info_test
+    def test_keyword(self):
+      # Make sure that C++ keywords work in the expression parser when using
+      # Objective-C++.
+      self.expect("expr -l objective-c++ -- constexpr int i = 3 + 3; i", substrs=["= 6"])