Revert "[lldb][darwin] force BuiltinHeadersInSystemModules to be always false (llvm#144913)"

This reverts commit 487581b.

Author: charles-zablit

lldb/include/lldb/Utility/XcodeSDK.h

@@ -93,6 +93,19 @@ class XcodeSDK {
   static bool SDKSupportsModules(Type type, llvm::VersionTuple version);
   static bool SDKSupportsModules(Type desired_type, const FileSpec &sdk_path);
 
+  /// Returns true if the SDK for the specified triple supports
+  /// builtin modules in system headers.
+  ///
+  /// NOTE: should be kept in sync with sdkSupportsBuiltinModules in
+  /// Toolchains/Darwin.cpp
+  ///
+  /// FIXME: this function will be removed once LLDB's ClangExpressionParser
+  /// constructs the compiler instance through the driver/toolchain. See \ref
+  /// SetupImportStdModuleLangOpts
+  ///
+  static bool SDKSupportsBuiltinModules(const llvm::Triple &target_triple,
+                                        llvm::VersionTuple sdk_version);
+
   /// Return the canonical SDK name, such as "macosx" for the macOS SDK.
   static std::string GetCanonicalName(Info info);
   /// Return the best-matching SDK type for a specific triple.

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

@@ -319,6 +319,49 @@ class ClangDiagnosticManagerAdapter : public clang::DiagnosticConsumer {
   StringRef m_filename;
 };
 
+/// Returns true if the SDK for the specified triple supports
+/// builtin modules in system headers. This is used to decide
+/// whether to pass -fbuiltin-headers-in-system-modules to
+/// the compiler instance when compiling the `std` module.
+static llvm::Expected<bool>
+sdkSupportsBuiltinModules(lldb_private::Target &target) {
+  auto arch_spec = target.GetArchitecture();
+  auto const &triple = arch_spec.GetTriple();
+  auto module_sp = target.GetExecutableModule();
+  if (!module_sp)
+    return llvm::createStringError("Executable module not found.");
+
+  // Get SDK path that the target was compiled against.
+  auto platform_sp = target.GetPlatform();
+  if (!platform_sp)
+    return llvm::createStringError("No Platform plugin found on target.");
+
+  auto sdk_or_err = platform_sp->GetSDKPathFromDebugInfo(*module_sp);
+  if (!sdk_or_err)
+    return sdk_or_err.takeError();
+
+  // Use the SDK path from debug-info to find a local matching SDK directory.
+  auto sdk_path_or_err =
+      HostInfo::GetSDKRoot(HostInfo::SDKOptions{std::move(sdk_or_err->first)});
+  if (!sdk_path_or_err)
+    return sdk_path_or_err.takeError();
+
+  auto VFS = FileSystem::Instance().GetVirtualFileSystem();
+  if (!VFS)
+    return llvm::createStringError("No virtual filesystem available.");
+
+  // Extract SDK version from the /path/to/some.sdk/SDKSettings.json
+  auto parsed_or_err = clang::parseDarwinSDKInfo(*VFS, *sdk_path_or_err);
+  if (!parsed_or_err)
+    return parsed_or_err.takeError();
+
+  auto maybe_sdk = *parsed_or_err;
+  if (!maybe_sdk)
+    return llvm::createStringError("Couldn't find Darwin SDK info.");
+
+  return XcodeSDK::SDKSupportsBuiltinModules(triple, maybe_sdk->getVersion());
+}
+
 static void SetupModuleHeaderPaths(CompilerInstance *compiler,
                                    std::vector<std::string> include_directories,
                                    lldb::TargetSP target_sp) {
@@ -662,6 +705,7 @@ static void SetupLangOpts(CompilerInstance &compiler,
 
 static void SetupImportStdModuleLangOpts(CompilerInstance &compiler,
                                          lldb_private::Target &target) {
+  Log *log = GetLog(LLDBLog::Expressions);
   LangOptions &lang_opts = compiler.getLangOpts();
   lang_opts.Modules = true;
   // We want to implicitly build modules.
@@ -679,7 +723,12 @@ static void SetupImportStdModuleLangOpts(CompilerInstance &compiler,
   lang_opts.GNUKeywords = true;
   lang_opts.CPlusPlus11 = true;
 
-  lang_opts.BuiltinHeadersInSystemModules = false;
+  if (auto supported_or_err = sdkSupportsBuiltinModules(target))
+    lang_opts.BuiltinHeadersInSystemModules = !*supported_or_err;
+  else
+    LLDB_LOG_ERROR(log, supported_or_err.takeError(),
+                   "Failed to determine BuiltinHeadersInSystemModules when "
+                   "setting up import-std-module: {0}");
 
   // The Darwin libc expects this macro to be set.
   lang_opts.GNUCVersion = 40201;

lldb/source/Utility/XcodeSDK.cpp

@@ -266,6 +266,27 @@ bool XcodeSDK::SupportsSwift() const {
   }
 }
 
+bool XcodeSDK::SDKSupportsBuiltinModules(const llvm::Triple &target_triple,
+                                         llvm::VersionTuple sdk_version) {
+  using namespace llvm;
+
+  switch (target_triple.getOS()) {
+  case Triple::OSType::MacOSX:
+    return sdk_version >= VersionTuple(15U);
+  case Triple::OSType::IOS:
+    return sdk_version >= VersionTuple(18U);
+  case Triple::OSType::TvOS:
+    return sdk_version >= VersionTuple(18U);
+  case Triple::OSType::WatchOS:
+    return sdk_version >= VersionTuple(11U);
+  case Triple::OSType::XROS:
+    return sdk_version >= VersionTuple(2U);
+  default:
+    // New SDKs support builtin modules from the start.
+    return true;
+  }
+}
+
 bool XcodeSDK::SDKSupportsModules(XcodeSDK::Type desired_type,
                                   const FileSpec &sdk_path) {
   ConstString last_path_component = sdk_path.GetFilename();