Implement gdb.execute_mi

This adds a new Python function, gdb.execute_mi, that can be used to
invoke an MI command but get the output as a Python object, rather
than a string.  This is done by implementing a new ui_out subclass
that builds a Python object.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=11688
Reviewed-By: Eli Zaretskii <eliz@gnu.org>

gdb/python/py-mi.c

@@ -0,0 +1,298 @@
+/* Python interface to MI commands
+
+   Copyright (C) 2023 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include "defs.h"
+#include "python-internal.h"
+#include "ui-out.h"
+#include "mi/mi-parse.h"
+
+/* A ui_out subclass that creates a Python object based on the data
+   that is passed in.  */
+
+class py_ui_out : public ui_out
+{
+public:
+
+  py_ui_out ()
+    : ui_out (fix_multi_location_breakpoint_output
+	      | fix_breakpoint_script_output)
+  {
+    do_begin (ui_out_type_tuple, nullptr);
+  }
+
+  bool can_emit_style_escape () const override
+  { return false; }
+
+  bool do_is_mi_like_p () const override
+  { return true; }
+
+  /* Return the Python object that was created.  If a Python error
+     occurred during the processing, set the Python error and return
+     nullptr.  */
+  PyObject *result ()
+  {
+    if (m_error.has_value ())
+      {
+	m_error->restore ();
+	return nullptr;
+      }
+    return current ().obj.release ();
+  }
+
+protected:
+
+  void do_progress_end () override { }
+  void do_progress_start () override { }
+  void do_progress_notify (const std::string &, const char *, double, double)
+    override
+  { }
+
+  void do_table_begin (int nbrofcols, int nr_rows, const char *tblid) override
+  {
+    do_begin (ui_out_type_list, tblid);
+  }
+  void do_table_body () override
+  { }
+  void do_table_end () override
+  {
+    do_end (ui_out_type_list);
+  }
+  void do_table_header (int width, ui_align align,
+			const std::string &col_name,
+			const std::string &col_hdr) override
+  { }
+
+  void do_begin (ui_out_type type, const char *id) override;
+  void do_end (ui_out_type type) override;
+
+  void do_field_signed (int fldno, int width, ui_align align,
+			const char *fldname, LONGEST value) override;
+  void do_field_unsigned (int fldno, int width, ui_align align,
+			  const char *fldname, ULONGEST value) override;
+
+  void do_field_skip (int fldno, int width, ui_align align,
+		      const char *fldname) override
+  { }
+
+  void do_field_string (int fldno, int width, ui_align align,
+			const char *fldname, const char *string,
+			const ui_file_style &style) override;
+  void do_field_fmt (int fldno, int width, ui_align align,
+		     const char *fldname, const ui_file_style &style,
+		     const char *format, va_list args) override
+    ATTRIBUTE_PRINTF (7, 0);
+
+  void do_spaces (int numspaces) override
+  { }
+
+  void do_text (const char *string) override
+  { }
+
+  void do_message (const ui_file_style &style,
+		   const char *format, va_list args)
+    override ATTRIBUTE_PRINTF (3,0)
+  { }
+
+  void do_wrap_hint (int indent) override
+  { }
+
+  void do_flush () override
+  { }
+
+  void do_redirect (struct ui_file *outstream) override
+  { }
+
+private:
+
+  /* When constructing Python objects, this class keeps a stack of
+     objects being constructed.  Each such object has this type.  */
+  struct object_desc
+  {
+    /* Name of the field (or empty for lists) that this object will
+       eventually become.  */
+    std::string field_name;
+    /* The object under construction.  */
+    gdbpy_ref<> obj;
+    /* The type of structure being created.  Note that tables are
+       treated as lists here.  */
+    ui_out_type type;
+  };
+
+  /* The stack of objects being created.  */
+  std::vector<object_desc> m_objects;
+
+  /* If an error occurred, this holds the exception information for
+     use by the 'release' method.  */
+  gdb::optional<gdbpy_err_fetch> m_error;
+
+  /* Return a reference to the object under construction.  */
+  object_desc &current ()
+  { return m_objects.back (); }
+
+  /* Add a new field to the current object under construction.  */
+  void add_field (const char *name, const gdbpy_ref<> &obj);
+};
+
+void
+py_ui_out::add_field (const char *name, const gdbpy_ref<> &obj)
+{
+  if (obj == nullptr)
+    {
+      m_error.emplace ();
+      return;
+    }
+
+  object_desc &desc = current ();
+  if (desc.type == ui_out_type_list)
+    {
+      if (PyList_Append (desc.obj.get (), obj.get ()) < 0)
+	m_error.emplace ();
+    }
+  else
+    {
+      if (PyDict_SetItemString (desc.obj.get (), name, obj.get ()) < 0)
+	m_error.emplace ();
+    }
+}
+
+void
+py_ui_out::do_begin (ui_out_type type, const char *id)
+{
+  if (m_error.has_value ())
+    return;
+
+  gdbpy_ref<> new_obj (type == ui_out_type_list
+		       ? PyList_New (0)
+		       : PyDict_New ());
+  if (new_obj == nullptr)
+    {
+      m_error.emplace ();
+      return;
+    }
+
+  object_desc new_desc;
+  if (id != nullptr)
+    new_desc.field_name = id;
+  new_desc.obj = std::move (new_obj);
+  new_desc.type = type;
+
+  m_objects.push_back (std::move (new_desc));
+}
+
+void
+py_ui_out::do_end (ui_out_type type)
+{
+  if (m_error.has_value ())
+    return;
+
+  object_desc new_obj = std::move (current ());
+  m_objects.pop_back ();
+  add_field (new_obj.field_name.c_str (), new_obj.obj);
+}
+
+void
+py_ui_out::do_field_signed (int fldno, int width, ui_align align,
+			    const char *fldname, LONGEST value)
+{
+  if (m_error.has_value ())
+    return;
+
+  gdbpy_ref<> val = gdb_py_object_from_longest (value);
+  add_field (fldname, val);
+}
+
+void
+py_ui_out::do_field_unsigned (int fldno, int width, ui_align align,
+			    const char *fldname, ULONGEST value)
+{
+  if (m_error.has_value ())
+    return;
+
+  gdbpy_ref<> val = gdb_py_object_from_ulongest (value);
+  add_field (fldname, val);
+}
+
+void
+py_ui_out::do_field_string (int fldno, int width, ui_align align,
+			    const char *fldname, const char *string,
+			    const ui_file_style &style)
+{
+  if (m_error.has_value ())
+    return;
+
+  gdbpy_ref<> val = host_string_to_python_string (string);
+  add_field (fldname, val);
+}
+
+void
+py_ui_out::do_field_fmt (int fldno, int width, ui_align align,
+			 const char *fldname, const ui_file_style &style,
+			 const char *format, va_list args)
+{
+  if (m_error.has_value ())
+    return;
+
+  std::string str = string_vprintf (format, args);
+  do_field_string (fldno, width, align, fldname, str.c_str (), style);
+}
+
+/* Implementation of the gdb.execute_mi command.  */
+
+PyObject *
+gdbpy_execute_mi_command (PyObject *self, PyObject *args, PyObject *kw)
+{
+  gdb::unique_xmalloc_ptr<char> mi_command;
+  std::vector<gdb::unique_xmalloc_ptr<char>> arg_strings;
+
+  Py_ssize_t n_args = PyTuple_Size (args);
+  if (n_args < 0)
+    return nullptr;
+
+  for (Py_ssize_t i = 0; i < n_args; ++i)
+    {
+      /* Note this returns a borrowed reference.  */
+      PyObject *arg = PyTuple_GetItem (args, i);
+      if (arg == nullptr)
+	return nullptr;
+      gdb::unique_xmalloc_ptr<char> str = python_string_to_host_string (arg);
+      if (str == nullptr)
+	return nullptr;
+      if (i == 0)
+	mi_command = std::move (str);
+      else
+	arg_strings.push_back (std::move (str));
+    }
+
+  py_ui_out uiout;
+
+  try
+    {
+      scoped_restore save_uiout = make_scoped_restore (&current_uiout, &uiout);
+      std::unique_ptr<struct mi_parse> parser
+	= mi_parse::make (std::move (mi_command), std::move (arg_strings));
+      mi_execute_command (parser.get ());
+    }
+  catch (const gdb_exception &except)
+    {
+      gdbpy_convert_exception (except);
+      return nullptr;
+    }
+
+  return uiout.result ();
+}

gdb/python/python-internal.h

@@ -483,6 +483,9 @@ struct symtab_and_line *sal_object_to_symtab_and_line (PyObject *obj);
 frame_info_ptr frame_object_to_frame_info (PyObject *frame_obj);
 struct gdbarch *arch_object_to_gdbarch (PyObject *obj);
 
+extern PyObject *gdbpy_execute_mi_command (PyObject *self, PyObject *args,
+					   PyObject *kw);
+
 /* Convert Python object OBJ to a program_space pointer.  OBJ must be a
    gdb.Progspace reference.  Return nullptr if the gdb.Progspace is not
    valid (see gdb.Progspace.is_valid), otherwise return the program_space

gdb/python/python.c

@@ -2484,6 +2484,11 @@ PyMethodDef python_GdbMethods[] =
 Evaluate command, a string, as a gdb CLI command.  Optionally returns\n\
 a Python String containing the output of the command if to_string is\n\
 set to True." },
+  { "execute_mi", (PyCFunction) gdbpy_execute_mi_command,
+    METH_VARARGS | METH_KEYWORDS,
+    "execute_mi (command, arg...) -> dictionary\n\
+Evaluate command, a string, as a gdb MI command.\n\
+Arguments (also strings) are passed to the command." },
   { "parameter", gdbpy_parameter, METH_VARARGS,
     "Return a gdb parameter's value" },