source/Plugins/ScriptInterpreter/Python/PythonExceptionState.cpp

//===-- PythonExceptionState.cpp --------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef LLDB_DISABLE_PYTHON

// LLDB Python header must be included first
#include "lldb-python.h"

#include "PythonExceptionState.h"

#include "llvm/ADT/StringRef.h"
#include "llvm/Support/raw_ostream.h"

using namespace lldb_private;

PythonExceptionState::PythonExceptionState(bool restore_on_exit)
    : m_restore_on_exit(restore_on_exit) {
  Acquire(restore_on_exit);
}

PythonExceptionState::~PythonExceptionState() {
  if (m_restore_on_exit)
    Restore();
}

void PythonExceptionState::Acquire(bool restore_on_exit) {
  // If a state is already acquired, the user needs to decide whether they want
  // to discard or restore it.  Don't allow the potential silent loss of a
  // valid state.
  assert(!IsError());

  if (!HasErrorOccurred())
    return;

  PyObject *py_type = nullptr;
  PyObject *py_value = nullptr;
  PyObject *py_traceback = nullptr;
  PyErr_Fetch(&py_type, &py_value, &py_traceback);
  // PyErr_Fetch clears the error flag.
  assert(!HasErrorOccurred());

  // Ownership of the objects returned by `PyErr_Fetch` is transferred to us.
  m_type.Reset(PyRefType::Owned, py_type);
  m_value.Reset(PyRefType::Owned, py_value);
  m_traceback.Reset(PyRefType::Owned, py_traceback);
  m_restore_on_exit = restore_on_exit;
}

void PythonExceptionState::Restore() {
  if (m_type.IsValid()) {
    // The documentation for PyErr_Restore says "Do not pass a null type and
    // non-null value or traceback.  So only restore if type was non-null to
    // begin with.  In this case we're passing ownership back to Python so
    // release them all.
    PyErr_Restore(m_type.release(), m_value.release(), m_traceback.release());
  }

  // After we restore, we should not hold onto the exception state.  Demand
  // that it be re-acquired.
  Discard();
}

void PythonExceptionState::Discard() {
  m_type.Reset();
  m_value.Reset();
  m_traceback.Reset();
}

void PythonExceptionState::Reset() {
  if (m_restore_on_exit)
    Restore();
  else
    Discard();
}

bool PythonExceptionState::HasErrorOccurred() { return PyErr_Occurred(); }

bool PythonExceptionState::IsError() const {
  return m_type.IsValid() || m_value.IsValid() || m_traceback.IsValid();
}

PythonObject PythonExceptionState::GetType() const { return m_type; }

PythonObject PythonExceptionState::GetValue() const { return m_value; }

PythonObject PythonExceptionState::GetTraceback() const { return m_traceback; }

std::string PythonExceptionState::Format() const {
  // Don't allow this function to modify the error state.
  PythonExceptionState state(true);

  std::string backtrace = ReadBacktrace();
  if (!IsError())
    return std::string();

  // It's possible that ReadPythonBacktrace generated another exception. If
  // this happens we have to clear the exception, because otherwise
  // PyObject_Str() will assert below.  That's why we needed to do the save /
  // restore at the beginning of this function.
  PythonExceptionState bt_error_state(false);

  std::string error_string;
  llvm::raw_string_ostream error_stream(error_string);
  error_stream << m_value.Str().GetString() << "\n";

  if (!bt_error_state.IsError()) {
    // If we were able to read the backtrace, just append it.
    error_stream << backtrace << "\n";
  } else {
    // Otherwise, append some information about why we were unable to obtain
    // the backtrace.
    PythonString bt_error = bt_error_state.GetValue().Str();
    error_stream << "An error occurred while retrieving the backtrace: "
                 << bt_error.GetString() << "\n";
  }
  return error_stream.str();
}

std::string PythonExceptionState::ReadBacktrace() const {
  std::string retval("backtrace unavailable");

  auto traceback_module = PythonModule::ImportModule("traceback");
#if PY_MAJOR_VERSION >= 3
  auto stringIO_module = PythonModule::ImportModule("io");
#else
  auto stringIO_module = PythonModule::ImportModule("StringIO");
#endif
  if (!m_traceback.IsAllocated())
    return retval;

  if (!traceback_module.IsAllocated() || !stringIO_module.IsAllocated())
    return retval;

  auto stringIO_builder =
      stringIO_module.ResolveName<PythonCallable>("StringIO");
  if (!stringIO_builder.IsAllocated())
    return retval;

  auto stringIO_buffer = stringIO_builder();
  if (!stringIO_buffer.IsAllocated())
    return retval;

  auto printTB = traceback_module.ResolveName<PythonCallable>("print_tb");
  if (!printTB.IsAllocated())
    return retval;

  auto printTB_result =
      printTB(m_traceback.get(), Py_None, stringIO_buffer.get());
  auto stringIO_getvalue =
      stringIO_buffer.ResolveName<PythonCallable>("getvalue");
  if (!stringIO_getvalue.IsAllocated())
    return retval;

  auto printTB_string = stringIO_getvalue().AsType<PythonString>();
  if (!printTB_string.IsAllocated())
    return retval;

  llvm::StringRef string_data(printTB_string.GetString());
  retval.assign(string_data.data(), string_data.size());

  return retval;
}

#endif