[lldb][PlatformDarwin] Only parse SDK from debug-info if target language is Objective-C

[Michael137]

Summary

The call to HostInfoMacOSX::GetSDKRoot can noticeably slow down the first
expression evaluation in an LLDB session. For C++ expressions we don't
actually ever use the results of the ClangDeclVendor, so getting the
flags right isn't necessary. Thus skip SDK parsing logic for C++
targets.

An alternative would be to entirely omit the setup of the
ClangDeclVendor (and other Objective-C machinery) for C++ targets.

[jingham]

It's fairly common for AppKit developers to use access to static methods under NSApplication to see the state of the application. Since you aren't actually accessing the frame variables for this purpose, it's also pretty common for those folks to do:

(lldb) process interrupt
(lldb) p [{NSApplication sharedApplication] someRequest]

That works today w/o having to specify a language. It would be good if this change didn't break that...

[aprantl]

Apart from Jim's comment (does this still work?) this seems like a reasonable heuristic.

lldb/source/Plugins/Platform/MacOSX/PlatformDarwin.cpp

 #include <algorithm>
 #include <memory>
 #include <mutex>
 #include <optional>
 
 #include "lldb/Breakpoint/BreakpointLocation.h"
 #include "lldb/Breakpoint/BreakpointSite.h"
 #include "lldb/Core/Debugger.h"
+#include "lldb/Target/Language.h"
 #include "lldb/Core/Module.h"
 #include "lldb/Core/ModuleSpec.h"
 #include "lldb/Core/PluginManager.h"
 #include "lldb/Core/Section.h"
 #include "lldb/Host/Host.h"
 #include "lldb/Host/HostInfo.h"
 #include "lldb/Host/XML.h"
 #include "lldb/Interpreter/CommandInterpreter.h"
case XcodeSDK::Type::unknown:
       return;
     }
     minimum_version_option << version.getAsString();
     options.emplace_back(std::string(minimum_version_option.GetString()));
   }
 
   FileSpec sysroot_spec;
 
-  if (target) {
+  if (target && Language::LanguageIsObjC(target->GetLanguage())) {
     if (ModuleSP exe_module_sp = target->GetExecutableModule()) {
       auto path_or_err = ResolveSDKPathFromDebugInfo(*exe_module_sp);
       if (path_or_err) {
         sysroot_spec = FileSpec(*path_or_err);
       } else {
         LLDB_LOG_ERROR(GetLog(LLDBLog::Types | LLDBLog::Host),
                        path_or_err.takeError(),
                        "Failed to resolve SDK path: {0}");