[lldb-dap] Support cancel requests and add explicit DAP structures.

[ashgti]

This is a refactor of lldb-dap focused on supporting cancel requests and well defined Debug Adapter Protocol (DAP) structures.

Existing request handlers today tend to use unstructured llvm::json::Object's to represent requests and replies. The lack of structure makes it hard for us to apply some unfirom handling around requests to better support cancellation. To address this, this change includes a new Protocol.h file with a set of well defined POD structures to represent the types in the DAP and includes toJSON/fromJSON serialization support.

Building on these types, this includes a new approach to registering request handlers with these new well defined types.

template <typename Args, typename Body>
void DAP::RegisterRequest(llvm::StringLiteral command,
                          RequestHandler<Args, Body> handler);
...
llvm::Expected<SourceResponseBody> request_source(DAP &dap, const SourceArguments &args) {
  SourceResponseBody body;
  ...
  if (/*some error*/)
    return llvm::make_error<DAPError>("msg");
  return std::move(body);
}
...
  dap.RegisterRequest("source", request_source);
...

The main features of this refactor are:

• Created a queue of pending protocol messages to allow for preemptive cancellations and active cancellations.
• A cleaner separation between the Debug Adapter Protocol types and lldb types that include serialization support toJSON/fromJSON.
• Improved error handling using toJSON/fromJSON.
• Unified handling of responses and errors.
• Unified handling of cancel requests.

This change include minimal support to implement the Debug Adapter Protocol 'source' request, 'evaluate' request and the 'exited' event.

[github-actions]

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff 998b28f19672ba49925e25f1a78c1252f017c247 481369f8107a43fd101e161c9bd9bb374e38f2af --extensions c,h,cpp -- lldb/test/API/tools/lldb-dap/cancel/main.c lldb/tools/lldb-dap/Protocol.cpp lldb/tools/lldb-dap/Protocol.h lldb/tools/lldb-dap/DAP.cpp lldb/tools/lldb-dap/DAP.h lldb/tools/lldb-dap/IOStream.cpp lldb/tools/lldb-dap/IOStream.h lldb/tools/lldb-dap/JSONUtils.cpp lldb/tools/lldb-dap/JSONUtils.h lldb/tools/lldb-dap/lldb-dap.cpp

View the diff from clang-format here.

diff --git a/lldb/tools/lldb-dap/DAP.cpp b/lldb/tools/lldb-dap/DAP.cpp
index 1bfed616bd..4ddb3491bd 100644
--- a/lldb/tools/lldb-dap/DAP.cpp
+++ b/lldb/tools/lldb-dap/DAP.cpp
@@ -930,7 +930,7 @@ llvm::Error DAP::Run() {
 
       if (protocol::Request *req = std::get_if<protocol::Request>(&next)) {
         active_request_seq = req->seq;
-        
+
         // If we have a request check if we should preemptively cancel it.
         bool cancelled = false;
         for (const auto &message : messages) {
diff --git a/lldb/tools/lldb-dap/DAP.h b/lldb/tools/lldb-dap/DAP.h
index 1bb58bff0d..2f4ab4abe5 100644
--- a/lldb/tools/lldb-dap/DAP.h
+++ b/lldb/tools/lldb-dap/DAP.h
@@ -162,21 +162,21 @@ struct Variables {
 
 struct StartDebuggingRequestHandler : public lldb::SBCommandPluginInterface {
   DAP &dap;
-  explicit StartDebuggingRequestHandler(DAP &d) : dap(d){};
+  explicit StartDebuggingRequestHandler(DAP &d) : dap(d) {};
   bool DoExecute(lldb::SBDebugger debugger, char **command,
                  lldb::SBCommandReturnObject &result) override;
 };
 
 struct ReplModeRequestHandler : public lldb::SBCommandPluginInterface {
   DAP &dap;
-  explicit ReplModeRequestHandler(DAP &d) : dap(d){};
+  explicit ReplModeRequestHandler(DAP &d) : dap(d) {};
   bool DoExecute(lldb::SBDebugger debugger, char **command,
                  lldb::SBCommandReturnObject &result) override;
 };
 
 struct SendEventRequestHandler : public lldb::SBCommandPluginInterface {
   DAP &dap;
-  explicit SendEventRequestHandler(DAP &d) : dap(d){};
+  explicit SendEventRequestHandler(DAP &d) : dap(d) {};
   bool DoExecute(lldb::SBDebugger debugger, char **command,
                  lldb::SBCommandReturnObject &result) override;
 };
diff --git a/lldb/tools/lldb-dap/Protocol.h b/lldb/tools/lldb-dap/Protocol.h
index b1c39a9a34..098180eab2 100644
--- a/lldb/tools/lldb-dap/Protocol.h
+++ b/lldb/tools/lldb-dap/Protocol.h
@@ -23,11 +23,11 @@
 #include "llvm/Support/JSON.h"
 #include <cstddef>
 #include <cstdint>
+#include <map>
 #include <optional>
 #include <string>
 #include <variant>
 #include <vector>
-#include <map>
 
 namespace lldb_dap {
 namespace protocol {