[lldb] Support CommandInterpreter print callbacks (#125006)

Xcode uses a pseudoterminal for the debugger console.

- The upside of this apporach is that it means that it can rely on
LLDB's IOHandlers for multiline and script input.
- The downside of this approach is that the command output is printed to
the PTY and you don't get a SBCommandReturnObject. Adrian added support
for inline diagnostics (#110901) and we'd like to access those from the
IDE.

This patch adds support for registering a callback in the command
interpreter that gives access to the `(SB)CommandReturnObject` right
before it will be printed. The callback implementation can choose
whether it likes to handle printing the result or defer to lldb. If the
callback indicated it handled the result, the command interpreter will
skip printing the result.

We considered a few other alternatives to solve this problem:

- The most obvious one is using `HandleCommand`, which returns a
`SBCommandReturnObject`. The problem with this approach is the multiline
input mentioned above. We would need a way to tell the IDE that it
should expect multiline input, which isn't known until LLDB starts
handling the command.
- To address the multiline issue,we considered exposing (some of the)
IOHandler machinery through the SB API. To solve this particular issue,
that would require reimplementing a ton of logic that already exists
today in the CommandInterpeter. Furthermore that seems like overkill
compared to the proposed solution.

rdar://141254310

lldb/bindings/python/python-swigsafecast.swig

@@ -9,6 +9,10 @@ PythonObject SWIGBridge::ToSWIGWrapper(std::unique_ptr<lldb::SBValue> value_sb)
   return ToSWIGHelper(value_sb.release(), SWIGTYPE_p_lldb__SBValue);
 }
 
+PythonObject SWIGBridge::ToSWIGWrapper(std::unique_ptr<lldb::SBCommandReturnObject> result_up) {
+  return ToSWIGHelper(result_up.release(), SWIGTYPE_p_lldb__SBCommandReturnObject);
+}
+
 PythonObject SWIGBridge::ToSWIGWrapper(lldb::ValueObjectSP value_sp) {
   return ToSWIGWrapper(std::unique_ptr<lldb::SBValue>(new lldb::SBValue(value_sp)));
 }

lldb/bindings/python/python-typemaps.swig

@@ -476,6 +476,25 @@ template <> bool SetNumberFromPyObject<double>(double &number, PyObject *obj) {
   $1 = $1 || PyCallable_Check(reinterpret_cast<PyObject *>($input));
 }
 
+// For lldb::SBCommandPrintCallback
+%typemap(in) (lldb::SBCommandPrintCallback callback, void *baton) {
+  if (!($input == Py_None ||
+        PyCallable_Check(reinterpret_cast<PyObject *>($input)))) {
+    PyErr_SetString(PyExc_TypeError, "Need a callable object or None!");
+    SWIG_fail;
+  }
+
+  // Don't lose the callback reference.
+  Py_INCREF($input);
+  $1 = LLDBSwigPythonCallPythonCommandPrintCallback;
+  $2 = $input;
+}
+
+%typemap(typecheck) (lldb::SBCommandPrintCallback callback, void *baton) {
+  $1 = $input == Py_None;
+  $1 = $1 || PyCallable_Check(reinterpret_cast<PyObject *>($input));
+}
+
 %typemap(in) (lldb::CommandOverrideCallback callback, void *baton) {
   if (!($input == Py_None ||
         PyCallable_Check(reinterpret_cast<PyObject *>($input)))) {

lldb/bindings/python/python-wrapper.swig

@@ -727,7 +727,7 @@ lldb_private::python::SWIGBridge::LLDBSwigPythonHandleOptionArgumentCompletionFo
     dict_sp->AddBooleanItem("no-completion", true);
     return dict_sp;
   }
-    
+
 
   // Convert the return dictionary to a DictionarySP.
   StructuredData::ObjectSP result_obj_sp = result.CreateStructuredObject();
@@ -753,7 +753,7 @@ bool lldb_private::python::SWIGBridge::LLDBSwigPythonCallParsedCommandObject(
   auto pfunc = self.ResolveName<PythonCallable>("__call__");
 
   if (!pfunc.IsAllocated()) {
-    cmd_retobj.AppendError("Could not find '__call__' method in implementation class"); 
+    cmd_retobj.AppendError("Could not find '__call__' method in implementation class");
     return false;
   }
 
@@ -1012,6 +1012,26 @@ static void LLDBSwigPythonCallPythonLogOutputCallback(const char *str,
   }
 }
 
+// For CommandPrintCallback functions
+static CommandReturnObjectCallbackResult LLDBSwigPythonCallPythonCommandPrintCallback(SBCommandReturnObject& result, void *callback_baton) {
+  SWIG_Python_Thread_Block swig_thread_block;
+
+  PyErr_Cleaner py_err_cleaner(true);
+
+  PythonObject result_arg = SWIGBridge::ToSWIGWrapper(
+      std::make_unique<SBCommandReturnObject>(result));
+  PythonCallable callable =
+      Retain<PythonCallable>(reinterpret_cast<PyObject *>(callback_baton));
+
+  if (!callable.IsValid())
+    return eCommandReturnObjectPrintCallbackSkipped;
+
+  PythonObject callback_result = callable(result_arg);
+
+  long long ret_val = unwrapOrSetPythonException(As<long long>(callback_result));
+  return (CommandReturnObjectCallbackResult)ret_val;
+}
+
 // For DebuggerTerminateCallback functions
 static void LLDBSwigPythonCallPythonSBDebuggerTerminateCallback(lldb::user_id_t debugger_id,
                                                       void *baton) {

lldb/include/lldb/API/SBCommandInterpreter.h

@@ -247,13 +247,13 @@ public:
                                        lldb::SBStringList &matches,
                                        lldb::SBStringList &descriptions);
 
-  /// Returns whether an interrupt flag was raised either by the SBDebugger - 
+  /// Returns whether an interrupt flag was raised either by the SBDebugger -
   /// when the function is not running on the RunCommandInterpreter thread, or
   /// by SBCommandInterpreter::InterruptCommand if it is.  If your code is doing
-  /// interruptible work, check this API periodically, and interrupt if it 
+  /// interruptible work, check this API periodically, and interrupt if it
   /// returns true.
   bool WasInterrupted() const;
-  
+
   /// Interrupts the command currently executing in the RunCommandInterpreter
   /// thread.
   ///
@@ -331,6 +331,8 @@ public:
   /// this list. Otherwise this list is empty.
   SBStructuredData GetTranscript();
 
+  void SetPrintCallback(lldb::SBCommandPrintCallback callback, void *baton);
+
 protected:
   friend class lldb_private::CommandPluginInterfaceImplementation;
 

lldb/include/lldb/API/SBDefines.h

@@ -144,6 +144,9 @@ typedef bool (*SBBreakpointHitCallback)(void *baton, lldb::SBProcess &process,
 typedef void (*SBDebuggerDestroyCallback)(lldb::user_id_t debugger_id,
                                           void *baton);
 
+typedef CommandReturnObjectCallbackResult (*SBCommandPrintCallback)(
+    lldb::SBCommandReturnObject &result, void *baton);
+
 typedef lldb::SBError (*SBPlatformLocateModuleCallback)(
     void *baton, const lldb::SBModuleSpec &module_spec,
     lldb::SBFileSpec &module_file_spec, lldb::SBFileSpec &symbol_file_spec);

lldb/include/lldb/Interpreter/CommandInterpreter.h

@@ -16,6 +16,7 @@
 #include "lldb/Interpreter/CommandObject.h"
 #include "lldb/Interpreter/ScriptInterpreter.h"
 #include "lldb/Utility/Args.h"
+#include "lldb/Utility/Baton.h"
 #include "lldb/Utility/Broadcaster.h"
 #include "lldb/Utility/CompletionRequest.h"
 #include "lldb/Utility/Event.h"
@@ -253,6 +254,10 @@ public:
     eCommandTypesAllThem = 0xFFFF  //< all commands
   };
 
+  using CommandReturnObjectCallback =
+      std::function<lldb::CommandReturnObjectCallbackResult(
+          CommandReturnObject &)>;
+
   // The CommandAlias and CommandInterpreter both have a hand in
   // substituting for alias commands.  They work by writing special tokens
   // in the template form of the Alias command, and then detecting them when the
@@ -664,6 +669,8 @@ public:
     ++m_command_usages[cmd_obj.GetCommandName()];
   }
 
+  void SetPrintCallback(CommandReturnObjectCallback callback);
+
   llvm::json::Value GetStatistics();
   const StructuredData::Array &GetTranscript() const;
 
@@ -774,6 +781,9 @@ private:
   std::vector<uint32_t> m_command_source_flags;
   CommandInterpreterRunResult m_result;
 
+  /// An optional callback to handle printing the CommandReturnObject.
+  CommandReturnObjectCallback m_print_callback;
+
   // The exit code the user has requested when calling the 'quit' command.
   // No value means the user hasn't set a custom exit code so far.
   std::optional<int> m_quit_exit_code;

lldb/include/lldb/lldb-enumerations.h

@@ -1368,6 +1368,15 @@ enum Severity {
   eSeverityInfo, // Equivalent to Remark used in clang.
 };
 
+/// Callback return value, indicating whether it handled printing the
+/// CommandReturnObject or deferred doing so to the CommandInterpreter.
+enum CommandReturnObjectCallbackResult {
+  /// The callback deferred printing the command return object.
+  eCommandReturnObjectPrintCallbackSkipped = 0,
+  /// The callback handled printing the command return object.
+  eCommandReturnObjectPrintCallbackHandled = 1,
+};
+
 } // namespace lldb
 
 #endif // LLDB_LLDB_ENUMERATIONS_H

lldb/source/API/SBCommandInterpreter.cpp

@@ -98,8 +98,8 @@ SBCommandInterpreter::SBCommandInterpreter(const SBCommandInterpreter &rhs)
 
 SBCommandInterpreter::~SBCommandInterpreter() = default;
 
-const SBCommandInterpreter &SBCommandInterpreter::
-operator=(const SBCommandInterpreter &rhs) {
+const SBCommandInterpreter &
+SBCommandInterpreter::operator=(const SBCommandInterpreter &rhs) {
   LLDB_INSTRUMENT_VA(this, rhs);
 
   m_opaque_ptr = rhs.m_opaque_ptr;
@@ -151,7 +151,7 @@ bool SBCommandInterpreter::WasInterrupted() const {
 
 bool SBCommandInterpreter::InterruptCommand() {
   LLDB_INSTRUMENT_VA(this);
-  
+
   return (IsValid() ? m_opaque_ptr->InterruptCommand() : false);
 }
 
@@ -222,8 +222,7 @@ void SBCommandInterpreter::HandleCommandsFromFile(
   if (override_context.get())
     m_opaque_ptr->HandleCommandsFromFile(tmp_spec,
                                          override_context.get()->Lock(true),
-                                         options.ref(),
-                                         result.ref());
+                                         options.ref(), result.ref());
 
   else
     m_opaque_ptr->HandleCommandsFromFile(tmp_spec, options.ref(), result.ref());
@@ -649,7 +648,8 @@ SBCommand::operator bool() const {
 const char *SBCommand::GetName() {
   LLDB_INSTRUMENT_VA(this);
 
-  return (IsValid() ? ConstString(m_opaque_sp->GetCommandName()).AsCString() : nullptr);
+  return (IsValid() ? ConstString(m_opaque_sp->GetCommandName()).AsCString()
+                    : nullptr);
 }
 
 const char *SBCommand::GetHelp() {
@@ -743,3 +743,15 @@ void SBCommand::SetFlags(uint32_t flags) {
   if (IsValid())
     m_opaque_sp->GetFlags().Set(flags);
 }
+
+void SBCommandInterpreter::SetPrintCallback(
+    lldb::SBCommandPrintCallback callback, void *baton) {
+  LLDB_INSTRUMENT_VA(this, callback, baton);
+
+  if (m_opaque_ptr)
+    m_opaque_ptr->SetPrintCallback(
+        [callback, baton](lldb_private::CommandReturnObject &result) {
+          SBCommandReturnObject sb_result(result);
+          return callback(sb_result, baton);
+        });
+}

lldb/source/Interpreter/CommandInterpreter.cpp

@@ -3186,30 +3186,40 @@ void CommandInterpreter::IOHandlerInputComplete(IOHandler &io_handler,
   if ((result.Succeeded() &&
        io_handler.GetFlags().Test(eHandleCommandFlagPrintResult)) ||
       io_handler.GetFlags().Test(eHandleCommandFlagPrintErrors)) {
-    // Display any inline diagnostics first.
-    const bool inline_diagnostics = !result.GetImmediateErrorStream() &&
-                                    GetDebugger().GetShowInlineDiagnostics();
-    if (inline_diagnostics) {
-      unsigned prompt_len = m_debugger.GetPrompt().size();
-      if (auto indent = result.GetDiagnosticIndent()) {
-        std::string diags =
-            result.GetInlineDiagnosticString(prompt_len + *indent);
-        PrintCommandOutput(io_handler, diags, true);
+    auto DefaultPrintCallback = [&](const CommandReturnObject &result) {
+      // Display any inline diagnostics first.
+      const bool inline_diagnostics = !result.GetImmediateErrorStream() &&
+                                      GetDebugger().GetShowInlineDiagnostics();
+      if (inline_diagnostics) {
+        unsigned prompt_len = m_debugger.GetPrompt().size();
+        if (auto indent = result.GetDiagnosticIndent()) {
+          std::string diags =
+              result.GetInlineDiagnosticString(prompt_len + *indent);
+          PrintCommandOutput(io_handler, diags, true);
+        }
       }
-    }
 
-    // Display any STDOUT/STDERR _prior_ to emitting the command result text.
-    GetProcessOutput();
+      // Display any STDOUT/STDERR _prior_ to emitting the command result text.
+      GetProcessOutput();
 
-    if (!result.GetImmediateOutputStream()) {
-      llvm::StringRef output = result.GetOutputString();
-      PrintCommandOutput(io_handler, output, true);
-    }
+      if (!result.GetImmediateOutputStream()) {
+        llvm::StringRef output = result.GetOutputString();
+        PrintCommandOutput(io_handler, output, true);
+      }
 
-    // Now emit the command error text from the command we just executed.
-    if (!result.GetImmediateErrorStream()) {
-      std::string error = result.GetErrorString(!inline_diagnostics);
-      PrintCommandOutput(io_handler, error, false);
+      // Now emit the command error text from the command we just executed.
+      if (!result.GetImmediateErrorStream()) {
+        std::string error = result.GetErrorString(!inline_diagnostics);
+        PrintCommandOutput(io_handler, error, false);
+      }
+    };
+
+    if (m_print_callback) {
+      const auto callback_result = m_print_callback(result);
+      if (callback_result == eCommandReturnObjectPrintCallbackSkipped)
+        DefaultPrintCallback(result);
+    } else {
+      DefaultPrintCallback(result);
     }
   }
 
@@ -3660,3 +3670,8 @@ llvm::json::Value CommandInterpreter::GetStatistics() {
 const StructuredData::Array &CommandInterpreter::GetTranscript() const {
   return m_transcript;
 }
+
+void CommandInterpreter::SetPrintCallback(
+    CommandReturnObjectCallback callback) {
+  m_print_callback = callback;
+}

lldb/source/Plugins/ScriptInterpreter/Python/SWIGPythonBridge.h

@@ -81,6 +81,8 @@ private:
 class SWIGBridge {
 public:
   static PythonObject ToSWIGWrapper(std::unique_ptr<lldb::SBValue> value_sb);
+  static PythonObject
+  ToSWIGWrapper(std::unique_ptr<lldb::SBCommandReturnObject> result_up);
   static PythonObject ToSWIGWrapper(lldb::ValueObjectSP value_sp);
   static PythonObject ToSWIGWrapper(lldb::TargetSP target_sp);
   static PythonObject ToSWIGWrapper(lldb::ProcessSP process_sp);
@@ -190,12 +192,11 @@ public:
                                   lldb::DebuggerSP debugger, const char *args,
                                   lldb_private::CommandReturnObject &cmd_retobj,
                                   lldb::ExecutionContextRefSP exe_ctx_ref_sp);
-  static bool
-  LLDBSwigPythonCallParsedCommandObject(PyObject *implementor,
-                                  lldb::DebuggerSP debugger,  
-                                  StructuredDataImpl &args_impl,
-                                  lldb_private::CommandReturnObject &cmd_retobj,
-                                  lldb::ExecutionContextRefSP exe_ctx_ref_sp);
+  static bool LLDBSwigPythonCallParsedCommandObject(
+      PyObject *implementor, lldb::DebuggerSP debugger,
+      StructuredDataImpl &args_impl,
+      lldb_private::CommandReturnObject &cmd_retobj,
+      lldb::ExecutionContextRefSP exe_ctx_ref_sp);
 
   static std::optional<std::string>
   LLDBSwigPythonGetRepeatCommandForScriptedCommand(PyObject *implementor,

lldb/test/API/python_api/interpreter_callback/Makefile

@@ -0,0 +1,3 @@
+C_SOURCES := main.c
+
+include Makefile.rules

lldb/test/API/python_api/interpreter_callback/TestCommandInterepterPrintCallback.py

@@ -0,0 +1,66 @@
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class CommandInterepterPrintCallbackTest(TestBase):
+    NO_DEBUG_INFO_TESTCASE = True
+
+    def run_command_interpreter_with_output_file(self, out_filename, input_str):
+        with open(out_filename, "w") as f:
+            self.dbg.SetOutputFileHandle(f, False)
+            self.dbg.SetInputString(input_str)
+            opts = lldb.SBCommandInterpreterRunOptions()
+            self.dbg.RunCommandInterpreter(True, False, opts, 0, False, False)
+
+    def test_command_interpreter_print_callback(self):
+        """Test the command interpreter print callback."""
+        self.build()
+        exe = self.getBuildArtifact("a.out")
+
+        target = self.dbg.CreateTarget(exe)
+        self.assertTrue(target, VALID_TARGET)
+
+        lldbutil.run_to_source_breakpoint(
+            self, "// Break here", lldb.SBFileSpec("main.c")
+        )
+
+        out_filename = self.getBuildArtifact("output")
+        ci = self.dbg.GetCommandInterpreter()
+        called = False
+
+        # The string we'll be looking for in the command output.
+        needle = "Show a list of all debugger commands"
+
+        # Test registering a callback that handles the printing. Make sure the
+        # result is passed to the callback and that we don't print the result.
+        def handling_callback(return_object):
+            nonlocal called
+            called = True
+            self.assertIn(needle, return_object.GetOutput())
+            return lldb.eCommandReturnObjectPrintCallbackHandled
+
+        ci.SetPrintCallback(handling_callback)
+        self.assertFalse(called)
+        self.run_command_interpreter_with_output_file(out_filename, "help help\n")
+        with open(out_filename, "r") as f:
+            self.assertNotIn(needle, f.read())
+
+        # Test registering a callback that defers the printing to lldb. Make
+        # sure the result is passed to the callback and that the result is
+        # printed by lldb.
+        def non_handling_callback(return_object):
+            nonlocal called
+            called = True
+            self.assertIn(needle, return_object.GetOutput())
+            return lldb.eCommandReturnObjectPrintCallbackSkipped
+
+        called = False
+        ci.SetPrintCallback(non_handling_callback)
+        self.assertFalse(called)
+        self.run_command_interpreter_with_output_file(out_filename, "help help\n")
+        self.assertTrue(called)
+
+        with open(out_filename, "r") as f:
+            self.assertIn(needle, f.read())

lldb/test/API/python_api/interpreter_callback/main.c

@@ -0,0 +1,6 @@
+#include <stdio.h>
+
+int main() {
+  int i = 1;
+  return i; // Break here
+}