[lldb][ClangExpressionParser] Set BuiltinHeadersInSystemModules depending on SDK version (#102309)

This patch changes the way we initialize `BuiltinHeadersInSystemModules`
which is one of the flags controlling Clang's behaviour when the Darwin
module is split into more fine-grained modules. The
ClangExpressionParser currently unconditionally sets
`-fbuiltin-headers-in-system-modules` when evaluating expressions with
the `target.import-std-module` setting. This flag should, however, be
set depending on the SDK version (which is what the Clang Darwin
toolchain does).

Unfortunately, the compiler instance that we create with
`ClangExpressionParser` never consults the Clang driver, and thus
doesn't correctly infer `BuiltinHeadersInSystemModules`. Note, this
isn't an issue with the `CompilerInstance` that the
`ClangModulesDeclVendor` creates because it uses the `createInovcation`
API, which calls into `Darwin::addClangTargetOptions`.

This patch mimicks how `sdkSupportsBuiltinModules` is used in
`Darwin::addClangTargetOptions`.

This ensures that the `import-std-module` API tests run cleanly
regardless of SDK version.

The plan is to eventually make the `CompilerInstance` construction in
`ClangExpressionParser` go through the driver, so we can avoid
duplicating the logic in LLDB. But we aren't there yet.

**Implementation**
* We look for the `SDKSettings.json` in the sysroot directory that we
found in DWARF (via `DW_AT_LLVM_sysroot`)
* Then parse this file and extract the SDK version number out of it
* Then mimick `sdkSupportsBuiltinModules` from `Toolchains/Darwin.cpp`
and set `BuiltinHeadersInSystemModules` based on it

rdar://116490281

Author: Michael137

lldb/include/lldb/Utility/XcodeSDK.h

@@ -85,6 +85,20 @@ class XcodeSDK {
   /// Whether LLDB feels confident importing Clang modules from this SDK.
   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

@@ -11,6 +11,7 @@
 #include "clang/AST/ExternalASTSource.h"
 #include "clang/AST/PrettyPrinter.h"
 #include "clang/Basic/Builtins.h"
+#include "clang/Basic/DarwinSDKInfo.h"
 #include "clang/Basic/DiagnosticIDs.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/TargetInfo.h"
@@ -39,6 +40,7 @@
 #include "llvm/ExecutionEngine/ExecutionEngine.h"
 #include "llvm/Support/CrashRecoveryContext.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/Error.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/TargetSelect.h"
 
@@ -91,6 +93,8 @@
 #include "lldb/Utility/StringList.h"
 
 #include "Plugins/LanguageRuntime/ObjC/ObjCLanguageRuntime.h"
+#include "Plugins/Platform/MacOSX/PlatformDarwin.h"
+#include "lldb/Utility/XcodeSDK.h"
 
 #include <cctype>
 #include <memory>
@@ -279,6 +283,49 @@ class ClangDiagnosticManagerAdapter : public clang::DiagnosticConsumer {
   std::string m_output;
 };
 
+/// 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) {
+#ifndef __APPLE__
+  return false;
+#else
+  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 sdk_or_err = PlatformDarwin::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());
+#endif
+}
+
 static void SetupModuleHeaderPaths(CompilerInstance *compiler,
                                    std::vector<std::string> include_directories,
                                    lldb::TargetSP target_sp) {
@@ -561,7 +608,9 @@ static void SetupLangOpts(CompilerInstance &compiler,
   lang_opts.NoBuiltin = true;
 }
 
-static void SetupImportStdModuleLangOpts(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.
@@ -578,7 +627,14 @@ static void SetupImportStdModuleLangOpts(CompilerInstance &compiler) {
   lang_opts.GNUMode = true;
   lang_opts.GNUKeywords = true;
   lang_opts.CPlusPlus11 = true;
-  lang_opts.BuiltinHeadersInSystemModules = true;
+
+  auto supported_or_err = sdkSupportsBuiltinModules(target);
+  if (supported_or_err)
+    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;
@@ -659,7 +715,7 @@ ClangExpressionParser::ClangExpressionParser(
   if (auto *clang_expr = dyn_cast<ClangUserExpression>(&m_expr);
       clang_expr && clang_expr->DidImportCxxModules()) {
     LLDB_LOG(log, "Adding lang options for importing C++ modules");
-    SetupImportStdModuleLangOpts(*m_compiler);
+    SetupImportStdModuleLangOpts(*m_compiler, *target_sp);
     SetupModuleHeaderPaths(m_compiler.get(), m_include_directories, target_sp);
   }
 

lldb/source/Utility/XcodeSDK.cpp

@@ -259,6 +259,27 @@ 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();