[lldb/Lua] add support for multiline scripted breakpoints

1 - Partial Statements

The interpreter loop runs every line it receives, so partial
Lua statements are not being handled properly. This is a problem for
multiline breakpoint scripts since the interpreter loop, for this
particular case, is just an abstraction to a partially parsed function
body declaration.

This patch addresses this issue and as a side effect improves the
general Lua interpreter loop as well. It's now possible to write partial
statements in the 'script' command.

Example:
   (lldb) script
   >>>   do
   ..>   local a = 123
   ..>   print(a)
   ..>   end
   123

The technique implemented is the same as the one employed by Lua's own REPL implementation.
Partial statements always errors out with the '<eof>' tag in the error
message.

2 - CheckSyntax in Lua.h

In order to support (1), we need an API for just checking the syntax of string buffers.

3 - Multiline scripted breakpoints

Finally, with all the base features implemented this feature is
straightforward. The interpreter loop behaves exactly the same, the
difference is that it will aggregate all Lua statements into the body of
the breakpoint function. An explicit 'quit' statement is needed to exit the
interpreter loop.

Example:
   (lldb) breakpoint command add -s lua
   Enter your Lua command(s). Type 'quit' to end.
   The commands are compiled as the body of the following Lua function
   function (frame, bp_loc, ...) end
   ..> print(456)
   ..> a = 123
   ..> quit

Differential Revision: https://reviews.llvm.org/D93481

lldb/source/Plugins/ScriptInterpreter/Lua/Lua.cpp

@@ -105,6 +105,23 @@ Lua::CallBreakpointCallback(void *baton, lldb::StackFrameSP stop_frame_sp,
                                                bp_loc_sp);
 }
 
+llvm::Error Lua::CheckSyntax(llvm::StringRef buffer) {
+  int error =
+      luaL_loadbuffer(m_lua_state, buffer.data(), buffer.size(), "buffer");
+  if (error == LUA_OK) {
+    // Pop buffer
+    lua_pop(m_lua_state, 1);
+    return llvm::Error::success();
+  }
+
+  llvm::Error e = llvm::make_error<llvm::StringError>(
+      llvm::formatv("{0}\n", lua_tostring(m_lua_state, -1)),
+      llvm::inconvertibleErrorCode());
+  // Pop error message from the stack.
+  lua_pop(m_lua_state, 1);
+  return e;
+}
+
 llvm::Error Lua::LoadModule(llvm::StringRef filename) {
   FileSpec file(filename);
   if (!FileSystem::Instance().Exists(file)) {

lldb/source/Plugins/ScriptInterpreter/Lua/Lua.h

@@ -36,6 +36,7 @@ public:
   CallBreakpointCallback(void *baton, lldb::StackFrameSP stop_frame_sp,
                          lldb::BreakpointLocationSP bp_loc_sp);
   llvm::Error LoadModule(llvm::StringRef filename);
+  llvm::Error CheckSyntax(llvm::StringRef buffer);
   llvm::Error ChangeIO(FILE *out, FILE *err);
 
 private:

lldb/source/Plugins/ScriptInterpreter/Lua/ScriptInterpreterLua.cpp

@@ -17,23 +17,33 @@
 #include "lldb/Utility/Stream.h"
 #include "lldb/Utility/StringList.h"
 #include "lldb/Utility/Timer.h"
+#include "llvm/ADT/StringRef.h"
 #include "llvm/Support/FormatAdapters.h"
 #include <memory>
+#include <vector>
 
 using namespace lldb;
 using namespace lldb_private;
 
 LLDB_PLUGIN_DEFINE(ScriptInterpreterLua)
 
+enum ActiveIOHandler {
+  eIOHandlerNone,
+  eIOHandlerBreakpoint,
+  eIOHandlerWatchpoint
+};
+
 class IOHandlerLuaInterpreter : public IOHandlerDelegate,
                                 public IOHandlerEditline {
 public:
   IOHandlerLuaInterpreter(Debugger &debugger,
-                          ScriptInterpreterLua &script_interpreter)
+                          ScriptInterpreterLua &script_interpreter,
+                          ActiveIOHandler active_io_handler = eIOHandlerNone)
       : IOHandlerEditline(debugger, IOHandler::Type::LuaInterpreter, "lua",
                           ">>> ", "..> ", true, debugger.GetUseColor(), 0,
                           *this, nullptr),
-        m_script_interpreter(script_interpreter) {
+        m_script_interpreter(script_interpreter),
+        m_active_io_handler(active_io_handler) {
     llvm::cantFail(m_script_interpreter.GetLua().ChangeIO(
         debugger.GetOutputFile().GetStream(),
         debugger.GetErrorFile().GetStream()));
@@ -44,20 +54,79 @@ public:
     llvm::cantFail(m_script_interpreter.LeaveSession());
   }
 
+  void IOHandlerActivated(IOHandler &io_handler, bool interactive) override {
+    const char *instructions = nullptr;
+    switch (m_active_io_handler) {
+    case eIOHandlerNone:
+    case eIOHandlerWatchpoint:
+      break;
+    case eIOHandlerBreakpoint:
+      instructions = "Enter your Lua command(s). Type 'quit' to end.\n"
+                     "The commands are compiled as the body of the following "
+                     "Lua function\n"
+                     "function (frame, bp_loc, ...) end\n";
+      SetPrompt(llvm::StringRef("..> "));
+      break;
+    }
+    if (instructions == nullptr)
+      return;
+    if (interactive)
+      *io_handler.GetOutputStreamFileSP() << instructions;
+  }
+
+  bool IOHandlerIsInputComplete(IOHandler &io_handler,
+                                StringList &lines) override {
+    size_t last = lines.GetSize() - 1;
+    if (IsQuitCommand(lines.GetStringAtIndex(last))) {
+      if (m_active_io_handler == eIOHandlerBreakpoint)
+        lines.DeleteStringAtIndex(last);
+      return true;
+    }
+    StreamString str;
+    lines.Join("\n", str);
+    if (llvm::Error E =
+            m_script_interpreter.GetLua().CheckSyntax(str.GetString())) {
+      std::string error_str = toString(std::move(E));
+      // Lua always errors out to incomplete code with '<eof>'
+      return error_str.find("<eof>") == std::string::npos;
+    }
+    // The breakpoint handler only exits with a explicit 'quit'
+    return m_active_io_handler != eIOHandlerBreakpoint;
+  }
+
   void IOHandlerInputComplete(IOHandler &io_handler,
                               std::string &data) override {
-    if (llvm::StringRef(data).rtrim() == "quit") {
+    switch (m_active_io_handler) {
+    case eIOHandlerBreakpoint: {
+      auto *bp_options_vec = static_cast<std::vector<BreakpointOptions *> *>(
+          io_handler.GetUserData());
+      for (auto *bp_options : *bp_options_vec) {
+        Status error = m_script_interpreter.SetBreakpointCommandCallback(
+            bp_options, data.c_str());
+        if (error.Fail())
+          *io_handler.GetErrorStreamFileSP() << error.AsCString() << '\n';
+      }
       io_handler.SetIsDone(true);
-      return;
-    }
-
-    if (llvm::Error error = m_script_interpreter.GetLua().Run(data)) {
-      *GetOutputStreamFileSP() << llvm::toString(std::move(error));
+    } break;
+    case eIOHandlerWatchpoint:
+      io_handler.SetIsDone(true);
+      break;
+    case eIOHandlerNone:
+      if (IsQuitCommand(data)) {
+        io_handler.SetIsDone(true);
+        return;
+      }
+      if (llvm::Error error = m_script_interpreter.GetLua().Run(data))
+        *io_handler.GetErrorStreamFileSP() << toString(std::move(error));
+      break;
     }
   }
 
 private:
   ScriptInterpreterLua &m_script_interpreter;
+  ActiveIOHandler m_active_io_handler;
+
+  bool IsQuitCommand(llvm::StringRef cmd) { return cmd.rtrim() == "quit"; }
 };
 
 ScriptInterpreterLua::ScriptInterpreterLua(Debugger &debugger)
@@ -205,6 +274,15 @@ bool ScriptInterpreterLua::BreakpointCallbackFunction(
   return *BoolOrErr;
 }
 
+void ScriptInterpreterLua::CollectDataForBreakpointCommandCallback(
+    std::vector<BreakpointOptions *> &bp_options_vec,
+    CommandReturnObject &result) {
+  IOHandlerSP io_handler_sp(
+      new IOHandlerLuaInterpreter(m_debugger, *this, eIOHandlerBreakpoint));
+  io_handler_sp->SetUserData(&bp_options_vec);
+  m_debugger.RunIOHandlerAsync(io_handler_sp);
+}
+
 Status ScriptInterpreterLua::SetBreakpointCommandCallback(
     BreakpointOptions *bp_options, const char *command_body_text) {
   Status error;

lldb/source/Plugins/ScriptInterpreter/Lua/ScriptInterpreterLua.h

@@ -65,6 +65,10 @@ public:
   llvm::Error EnterSession(lldb::user_id_t debugger_id);
   llvm::Error LeaveSession();
 
+  void CollectDataForBreakpointCommandCallback(
+      std::vector<BreakpointOptions *> &bp_options_vec,
+      CommandReturnObject &result) override;
+
   Status SetBreakpointCommandCallback(BreakpointOptions *bp_options,
                                       const char *command_body_text) override;
 

lldb/test/Shell/ScriptInterpreter/Lua/breakpoint_callback.test

@@ -1,5 +1,13 @@
 # REQUIRES: lua
-# RUN: %lldb -s %s --script-language lua 2>&1 | FileCheck %s
+# RUN: echo "int main() { return 0; }" | %clang_host -x c - -o %t
+# RUN: %lldb -s %s --script-language lua %t 2>&1 | FileCheck %s
 b main
 breakpoint command add -s lua
-# CHECK: error: This script interpreter does not support breakpoint callbacks
+local a = 123
+print(a)
+quit
+run
+# CHECK: 123
+breakpoint command add -s lua
+789_nil
+# CHECK: unexpected symbol near '789'

lldb/test/Shell/ScriptInterpreter/Lua/partial_statements.test

@@ -0,0 +1,15 @@
+# REQUIRES: lua
+# RUN: %lldb -s %s --script-language lua 2>&1 | FileCheck %s
+script
+do
+local a = 123
+print(a)
+end
+# CHECK: 123
+str = 'hello there!'
+function callme()
+print(str)
+end
+callme()
+# CHECK: hello there!
+# CHECK-NOT: error