[Windows] Introduce a switch for the `lldb-server` mode on Windows

[aleksandr.urakov]

Summary

This patch introduces a switch, based on the environment variable LLDB_USE_LLDB_SERVER, to determine whether to use the ProcessWindows plugin (the old way) or the lldb-server way for debugging on Windows.

[labath]

Sounds reasonable. Thanks for doing this.

[amccarth]

Why an environment variable rather than a command line option?

[aleksandr.urakov]

I've made it in the way similar to Zachary have made for the SymbolFileNativePDB plugin. An environment variable could be more convenient e.g. to run a bunch of tests using the lldb-test option.

[aleksandr.urakov]

In D68258#1690756, @aleksandr.urakov wrote:

I've made it in the way similar to Zachary have made for the SymbolFileNativePDB plugin. An environment variable could be more convenient e.g. to run a bunch of tests using the lldb-test option.

I'm sorry, sure I mean the lldb-server option.

[amccarth]

In D68258#1690757, @aleksandr.urakov wrote:

In D68258#1690756, @aleksandr.urakov wrote:

I've made it in the way similar to Zachary have made for the SymbolFileNativePDB plugin. An environment variable could be more convenient e.g. to run a bunch of tests using the lldb-test option.

The environment variable for using the native PDB was always intended to be temporary, since the native PDB reader would eventually be the only PDB reader.

In general, I find environment variables harder to manage (especially on Windows) than command line options. They're invisible global variables that compound all the environmental issues that make building and testing so flaky and hard to diagnose.

[labath]

In D68258#1691485, @amccarth wrote:

The environment variable for using the native PDB was always intended to be temporary, since the native PDB reader would eventually be the only PDB reader.

I don't know whether that's good or bad, but I think this variable is precisely the same kind of "temporary" as the other one. :)

[amccarth]

Given Pavel's comment, this LGTM.

[aleksandr.urakov]

Hello! I am sorry for a delay with reply, I was OOO. Thanks all for the review!

lldb/source/Plugins/Process/Windows/Common/ProcessWindows.cpp

 namespace lldb_private {
 
 ProcessSP ProcessWindows::CreateInstance(lldb::TargetSP target_sp,
                                          lldb::ListenerSP listener_sp,
                                          const FileSpec *) {
   return ProcessSP(new ProcessWindows(target_sp, listener_sp));
 }
 
+static bool ShouldUseLLDBServer() {
+  llvm::StringRef use_lldb_server = ::getenv("LLDB_USE_LLDB_SERVER");
+  return use_lldb_server.equals_lower("on") ||
+         use_lldb_server.equals_lower("yes") ||
+         use_lldb_server.equals_lower("1") ||
+         use_lldb_server.equals_lower("true");
+}
+
 void ProcessWindows::Initialize() {
+  if (!ShouldUseLLDBServer()) {
     static llvm::once_flag g_once_flag;
 
     llvm::call_once(g_once_flag, []() {
       PluginManager::RegisterPlugin(GetPluginNameStatic(),
-                                  GetPluginDescriptionStatic(), CreateInstance);
+                                    GetPluginDescriptionStatic(),
+                                    CreateInstance);
     });
   }
+}
 
 void ProcessWindows::Terminate() {}
 
 lldb_private::ConstString ProcessWindows::GetPluginNameStatic() {
   static ConstString g_name("windows");
   return g_name;
 }