[lldb/Lua] Make lldb.debugger et al available to Lua

The Python script interpreter makes the current debugger, target,
process, thread and frame available to interactive scripting sessions
through convenience variables. This patch does the same for Lua.

Differential revision: https://reviews.llvm.org/D71801

4 files changed, 40 insertions, 3 deletions

diff --git a/lldb/source/Plugins/ScriptInterpreter/Lua/Lua.cpp b/lldb/source/Plugins/ScriptInterpreter/Lua/Lua.cpp
index dc64139..1dd0a9e 100644
--- a/lldb/source/Plugins/ScriptInterpreter/Lua/Lua.cpp
+++ b/lldb/source/Plugins/ScriptInterpreter/Lua/Lua.cpp
@@ -10,9 +10,9 @@
 #include "llvm/Support/FormatVariadic.h"
 
 using namespace lldb_private;
+using namespace lldb;
 
 llvm::Error Lua::Run(llvm::StringRef buffer) {
-  std::lock_guard<std::mutex> lock(m_mutex);
   int error =
       luaL_loadbuffer(m_lua_state, buffer.data(), buffer.size(), "buffer") ||
       lua_pcall(m_lua_state, 0, 0, 0);
diff --git a/lldb/source/Plugins/ScriptInterpreter/Lua/Lua.h b/lldb/source/Plugins/ScriptInterpreter/Lua/Lua.h
index ed1d159..adc6c61 100644
--- a/lldb/source/Plugins/ScriptInterpreter/Lua/Lua.h
+++ b/lldb/source/Plugins/ScriptInterpreter/Lua/Lua.h
@@ -9,6 +9,7 @@
 #ifndef liblldb_Lua_h_
 #define liblldb_Lua_h_
 
+#include "lldb/lldb-types.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Error.h"
 
@@ -38,7 +39,6 @@ public:
   llvm::Error Run(llvm::StringRef buffer);
 
 private:
-  std::mutex m_mutex;
   lua_State *m_lua_state;
 };
 
diff --git a/lldb/source/Plugins/ScriptInterpreter/Lua/ScriptInterpreterLua.cpp b/lldb/source/Plugins/ScriptInterpreter/Lua/ScriptInterpreterLua.cpp
index d5423b7..e46851c 100644
--- a/lldb/source/Plugins/ScriptInterpreter/Lua/ScriptInterpreterLua.cpp
+++ b/lldb/source/Plugins/ScriptInterpreter/Lua/ScriptInterpreterLua.cpp
@@ -27,7 +27,13 @@ public:
       : IOHandlerEditline(debugger, IOHandler::Type::LuaInterpreter, "lua",
                           ">>> ", "..> ", true, debugger.GetUseColor(), 0,
                           *this, nullptr),
-        m_script_interpreter(script_interpreter) {}
+        m_script_interpreter(script_interpreter) {
+    llvm::cantFail(m_script_interpreter.EnterSession(debugger.GetID()));
+  }
+
+  ~IOHandlerLuaInterpreter() {
+    llvm::cantFail(m_script_interpreter.LeaveSession());
+  }
 
   void IOHandlerInputComplete(IOHandler &io_handler,
                               std::string &data) override {
@@ -89,6 +95,33 @@ void ScriptInterpreterLua::Initialize() {
 
 void ScriptInterpreterLua::Terminate() {}
 
+llvm::Error ScriptInterpreterLua::EnterSession(user_id_t debugger_id) {
+  if (m_session_is_active)
+    return llvm::Error::success();
+
+  const char *fmt_str =
+      "lldb.debugger = lldb.SBDebugger.FindDebuggerWithID({0}); "
+      "lldb.target = lldb.debugger:GetSelectedTarget(); "
+      "lldb.process = lldb.target:GetProcess(); "
+      "lldb.thread = lldb.process:GetSelectedThread(); "
+      "lldb.frame = lldb.thread:GetSelectedFrame()";
+  return m_lua->Run(llvm::formatv(fmt_str, debugger_id).str());
+}
+
+llvm::Error ScriptInterpreterLua::LeaveSession() {
+  if (!m_session_is_active)
+    return llvm::Error::success();
+
+  m_session_is_active = false;
+
+  llvm::StringRef str = "lldb.debugger = nil; "
+                        "lldb.target = nil; "
+                        "lldb.process = nil; "
+                        "lldb.thread = nil; "
+                        "lldb.frame = nil";
+  return m_lua->Run(str);
+}
+
 lldb::ScriptInterpreterSP
 ScriptInterpreterLua::CreateInstance(Debugger &debugger) {
   return std::make_shared<ScriptInterpreterLua>(debugger);
diff --git a/lldb/source/Plugins/ScriptInterpreter/Lua/ScriptInterpreterLua.h b/lldb/source/Plugins/ScriptInterpreter/Lua/ScriptInterpreterLua.h
index b34c7d0..550e1035 100644
--- a/lldb/source/Plugins/ScriptInterpreter/Lua/ScriptInterpreterLua.h
+++ b/lldb/source/Plugins/ScriptInterpreter/Lua/ScriptInterpreterLua.h
@@ -43,8 +43,12 @@ public:
 
   Lua &GetLua();
 
+  llvm::Error EnterSession(lldb::user_id_t debugger_id);
+  llvm::Error LeaveSession();
+
 private:
   std::unique_ptr<Lua> m_lua;
+  bool m_session_is_active = false;
 };
 
 } // namespace lldb_private