gdb/python/py-prettyprint.c

   1 /* Python pretty-printing
   2
   3    Copyright (C) 2008-2018 Free Software Foundation, Inc.
   4
   5    This file is part of GDB.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  19
  20 #include "defs.h"
  21 #include "objfiles.h"
  22 #include "symtab.h"
  23 #include "language.h"
  24 #include "valprint.h"
  25 #include "extension-priv.h"
  26 #include "python.h"
  27 #include "python-internal.h"
  28 #include "py-ref.h"
  29
  30 /* Return type of print_string_repr.  */
  31
  32 enum string_repr_result
  33   {
  34     /* The string method returned None.  */
  35     string_repr_none,
  36     /* The string method had an error.  */
  37     string_repr_error,
  38     /* Everything ok.  */
  39     string_repr_ok
  40   };
  41
  42 /* Helper function for find_pretty_printer which iterates over a list,
  43    calls each function and inspects output.  This will return a
  44    printer object if one recognizes VALUE.  If no printer is found, it
  45    will return None.  On error, it will set the Python error and
  46    return NULL.  */
  47
  48 static PyObject *
  49 search_pp_list (PyObject *list, PyObject *value)
  50 {
  51   Py_ssize_t pp_list_size, list_index;
  52
  53   pp_list_size = PyList_Size (list);
  54   for (list_index = 0; list_index < pp_list_size; list_index++)
  55     {
  56       PyObject *function = PyList_GetItem (list, list_index);
  57       if (! function)
  58         return NULL;
  59
  60       /* Skip if disabled.  */
  61       if (PyObject_HasAttr (function, gdbpy_enabled_cst))
  62         {
  63           gdbpy_ref<> attr (PyObject_GetAttr (function, gdbpy_enabled_cst));
  64           int cmp;
  65
  66           if (attr == NULL)
  67             return NULL;
  68           cmp = PyObject_IsTrue (attr.get ());
  69           if (cmp == -1)
  70             return NULL;
  71
  72           if (!cmp)
  73             continue;
  74         }
  75
  76       gdbpy_ref<> printer (PyObject_CallFunctionObjArgs (function, value,
  77                                                          NULL));
  78       if (printer == NULL)
  79         return NULL;
  80       else if (printer != Py_None)
  81         return printer.release ();
  82     }
  83
  84   Py_RETURN_NONE;
  85 }
  86
  87 /* Subroutine of find_pretty_printer to simplify it.
  88    Look for a pretty-printer to print VALUE in all objfiles.
  89    The result is NULL if there's an error and the search should be terminated.
  90    The result is Py_None, suitably inc-ref'd, if no pretty-printer was found.
  91    Otherwise the result is the pretty-printer function, suitably inc-ref'd.  */
  92
  93 static PyObject *
  94 find_pretty_printer_from_objfiles (PyObject *value)
  95 {
  96   struct objfile *obj;
  97
  98   ALL_OBJFILES (obj)
  99   {
 100     gdbpy_ref<> objf = objfile_to_objfile_object (obj);
 101     if (objf == NULL)
 102       {
 103         /* Ignore the error and continue.  */
 104         PyErr_Clear ();
 105         continue;
 106       }
 107
 108     gdbpy_ref<> pp_list (objfpy_get_printers (objf.get (), NULL));
 109     gdbpy_ref<> function (search_pp_list (pp_list.get (), value));
 110
 111     /* If there is an error in any objfile list, abort the search and exit.  */
 112     if (function == NULL)
 113       return NULL;
 114
 115     if (function != Py_None)
 116       return function.release ();
 117   }
 118
 119   Py_RETURN_NONE;
 120 }
 121
 122 /* Subroutine of find_pretty_printer to simplify it.
 123    Look for a pretty-printer to print VALUE in the current program space.
 124    The result is NULL if there's an error and the search should be terminated.
 125    The result is Py_None, suitably inc-ref'd, if no pretty-printer was found.
 126    Otherwise the result is the pretty-printer function, suitably inc-ref'd.  */
 127
 128 static PyObject *
 129 find_pretty_printer_from_progspace (PyObject *value)
 130 {
 131   gdbpy_ref<> obj = pspace_to_pspace_object (current_program_space);
 132
 133   if (obj == NULL)
 134     return NULL;
 135   gdbpy_ref<> pp_list (pspy_get_printers (obj.get (), NULL));
 136   return search_pp_list (pp_list.get (), value);
 137 }
 138
 139 /* Subroutine of find_pretty_printer to simplify it.
 140    Look for a pretty-printer to print VALUE in the gdb module.
 141    The result is NULL if there's an error and the search should be terminated.
 142    The result is Py_None, suitably inc-ref'd, if no pretty-printer was found.
 143    Otherwise the result is the pretty-printer function, suitably inc-ref'd.  */
 144
 145 static PyObject *
 146 find_pretty_printer_from_gdb (PyObject *value)
 147 {
 148   /* Fetch the global pretty printer list.  */
 149   if (gdb_python_module == NULL
 150       || ! PyObject_HasAttrString (gdb_python_module, "pretty_printers"))
 151     Py_RETURN_NONE;
 152   gdbpy_ref<> pp_list (PyObject_GetAttrString (gdb_python_module,
 153                                                "pretty_printers"));
 154   if (pp_list == NULL || ! PyList_Check (pp_list.get ()))
 155     Py_RETURN_NONE;
 156
 157   return search_pp_list (pp_list.get (), value);
 158 }
 159
 160 /* Find the pretty-printing constructor function for VALUE.  If no
 161    pretty-printer exists, return None.  If one exists, return a new
 162    reference.  On error, set the Python error and return NULL.  */
 163
 164 static PyObject *
 165 find_pretty_printer (PyObject *value)
 166 {
 167   /* Look at the pretty-printer list for each objfile
 168      in the current program-space.  */
 169   gdbpy_ref<> function (find_pretty_printer_from_objfiles (value));
 170   if (function == NULL || function != Py_None)
 171     return function.release ();
 172
 173   /* Look at the pretty-printer list for the current program-space.  */
 174   function.reset (find_pretty_printer_from_progspace (value));
 175   if (function == NULL || function != Py_None)
 176     return function.release ();
 177
 178   /* Look at the pretty-printer list in the gdb module.  */
 179   return find_pretty_printer_from_gdb (value);
 180 }
 181
 182 /* Pretty-print a single value, via the printer object PRINTER.
 183    If the function returns a string, a PyObject containing the string
 184    is returned.  If the function returns Py_NONE that means the pretty
 185    printer returned the Python None as a value.  Otherwise, if the
 186    function returns a value,  *OUT_VALUE is set to the value, and NULL
 187    is returned.  On error, *OUT_VALUE is set to NULL, NULL is
 188    returned, with a python exception set.  */
 189
 190 static gdbpy_ref<>
 191 pretty_print_one_value (PyObject *printer, struct value **out_value)
 192 {
 193   gdbpy_ref<> result;
 194
 195   *out_value = NULL;
 196   TRY
 197     {
 198       if (!PyObject_HasAttr (printer, gdbpy_to_string_cst))
 199         result = gdbpy_ref<>::new_reference (Py_None);
 200       else
 201         {
 202           result.reset (PyObject_CallMethodObjArgs (printer, gdbpy_to_string_cst,
 203                                                     NULL));
 204           if (result != NULL)
 205             {
 206               if (! gdbpy_is_string (result.get ())
 207                   && ! gdbpy_is_lazy_string (result.get ())
 208                   && result != Py_None)
 209                 {
 210                   *out_value = convert_value_from_python (result.get ());
 211                   if (PyErr_Occurred ())
 212                     *out_value = NULL;
 213                   result = NULL;
 214                 }
 215             }
 216         }
 217     }
 218   CATCH (except, RETURN_MASK_ALL)
 219     {
 220     }
 221   END_CATCH
 222
 223   return result;
 224 }
 225
 226 /* Return the display hint for the object printer, PRINTER.  Return
 227    NULL if there is no display_hint method, or if the method did not
 228    return a string.  On error, print stack trace and return NULL.  On
 229    success, return an xmalloc()d string.  */
 230 gdb::unique_xmalloc_ptr<char>
 231 gdbpy_get_display_hint (PyObject *printer)
 232 {
 233   gdb::unique_xmalloc_ptr<char> result;
 234
 235   if (! PyObject_HasAttr (printer, gdbpy_display_hint_cst))
 236     return NULL;
 237
 238   gdbpy_ref<> hint (PyObject_CallMethodObjArgs (printer, gdbpy_display_hint_cst,
 239                                                 NULL));
 240   if (hint != NULL)
 241     {
 242       if (gdbpy_is_string (hint.get ()))
 243         {
 244           result = python_string_to_host_string (hint.get ());
 245           if (result == NULL)
 246             gdbpy_print_stack ();
 247         }
 248     }
 249   else
 250     gdbpy_print_stack ();
 251
 252   return result;
 253 }
 254
 255 /* A wrapper for gdbpy_print_stack that ignores MemoryError.  */
 256
 257 static void
 258 print_stack_unless_memory_error (struct ui_file *stream)
 259 {
 260   if (PyErr_ExceptionMatches (gdbpy_gdb_memory_error))
 261     {
 262       PyObject *type, *value, *trace;
 263
 264       PyErr_Fetch (&type, &value, &trace);
 265
 266       gdbpy_ref<> type_ref (type);
 267       gdbpy_ref<> value_ref (value);
 268       gdbpy_ref<> trace_ref (trace);
 269
 270       gdb::unique_xmalloc_ptr<char>
 271         msg (gdbpy_exception_to_string (type, value));
 272
 273       if (msg == NULL || *msg == '\0')
 274         fprintf_filtered (stream, _("<error reading variable>"));
 275       else
 276         fprintf_filtered (stream, _("<error reading variable: %s>"),
 277                           msg.get ());
 278     }
 279   else
 280     gdbpy_print_stack ();
 281 }
 282
 283 /* Helper for gdbpy_apply_val_pretty_printer which calls to_string and
 284    formats the result.  */
 285
 286 static enum string_repr_result
 287 print_string_repr (PyObject *printer, const char *hint,
 288                    struct ui_file *stream, int recurse,
 289                    const struct value_print_options *options,
 290                    const struct language_defn *language,
 291                    struct gdbarch *gdbarch)
 292 {
 293   struct value *replacement = NULL;
 294   enum string_repr_result result = string_repr_ok;
 295
 296   gdbpy_ref<> py_str = pretty_print_one_value (printer, &replacement);
 297   if (py_str != NULL)
 298     {
 299       if (py_str == Py_None)
 300         result = string_repr_none;
 301       else if (gdbpy_is_lazy_string (py_str.get ()))
 302         {
 303           CORE_ADDR addr;
 304           long length;
 305           struct type *type;
 306           gdb::unique_xmalloc_ptr<char> encoding;
 307           struct value_print_options local_opts = *options;
 308
 309           gdbpy_extract_lazy_string (py_str.get (), &addr, &type,
 310                                      &length, &encoding);
 311
 312           local_opts.addressprint = 0;
 313           val_print_string (type, encoding.get (), addr, (int) length,
 314                             stream, &local_opts);
 315         }
 316       else
 317         {
 318           gdbpy_ref<> string
 319             = python_string_to_target_python_string (py_str.get ());
 320           if (string != NULL)
 321             {
 322               char *output;
 323               long length;
 324               struct type *type;
 325
 326 #ifdef IS_PY3K
 327               output = PyBytes_AS_STRING (string.get ());
 328               length = PyBytes_GET_SIZE (string.get ());
 329 #else
 330               output = PyString_AsString (string.get ());
 331               length = PyString_Size (string.get ());
 332 #endif
 333               type = builtin_type (gdbarch)->builtin_char;
 334
 335               if (hint && !strcmp (hint, "string"))
 336                 LA_PRINT_STRING (stream, type, (gdb_byte *) output,
 337                                  length, NULL, 0, options);
 338               else
 339                 fputs_filtered (output, stream);
 340             }
 341           else
 342             {
 343               result = string_repr_error;
 344               print_stack_unless_memory_error (stream);
 345             }
 346         }
 347     }
 348   else if (replacement)
 349     {
 350       struct value_print_options opts = *options;
 351
 352       opts.addressprint = 0;
 353       common_val_print (replacement, stream, recurse, &opts, language);
 354     }
 355   else
 356     {
 357       result = string_repr_error;
 358       print_stack_unless_memory_error (stream);
 359     }
 360
 361   return result;
 362 }
 363
 364 #ifndef IS_PY3K
 365
 366 /* Create a dummy PyFrameObject, needed to work around
 367    a Python-2.4 bug with generators.  */
 368 class dummy_python_frame
 369 {
 370  public:
 371
 372   dummy_python_frame ();
 373
 374   ~dummy_python_frame ()
 375   {
 376     if (m_valid)
 377       m_tstate->frame = m_saved_frame;
 378   }
 379
 380   bool failed () const
 381   {
 382     return !m_valid;
 383   }
 384
 385  private:
 386
 387   bool m_valid;
 388   PyFrameObject *m_saved_frame;
 389   gdbpy_ref<> m_frame;
 390   PyThreadState *m_tstate;
 391 };
 392
 393 dummy_python_frame::dummy_python_frame ()
 394 : m_valid (false),
 395   m_saved_frame (NULL),
 396   m_tstate (NULL)
 397 {
 398   PyCodeObject *code;
 399   PyFrameObject *frame;
 400
 401   gdbpy_ref<> empty_string (PyString_FromString (""));
 402   if (empty_string == NULL)
 403     return;
 404
 405   gdbpy_ref<> null_tuple (PyTuple_New (0));
 406   if (null_tuple == NULL)
 407     return;
 408
 409   code = PyCode_New (0,                   /* argcount */
 410                      0,                   /* locals */
 411                      0,                   /* stacksize */
 412                      0,                   /* flags */
 413                      empty_string.get (), /* code */
 414                      null_tuple.get (),   /* consts */
 415                      null_tuple.get (),   /* names */
 416                      null_tuple.get (),   /* varnames */
 417 #if PYTHON_API_VERSION >= 1010
 418                      null_tuple.get (),   /* freevars */
 419                      null_tuple.get (),   /* cellvars */
 420 #endif
 421                      empty_string.get (), /* filename */
 422                      empty_string.get (), /* name */
 423                      1,                   /* firstlineno */
 424                      empty_string.get ()  /* lnotab */
 425                      );
 426   if (code == NULL)
 427     return;
 428   gdbpy_ref<> code_holder ((PyObject *) code);
 429
 430   gdbpy_ref<> globals (PyDict_New ());
 431   if (globals == NULL)
 432     return;
 433
 434   m_tstate = PyThreadState_GET ();
 435   frame = PyFrame_New (m_tstate, code, globals.get (), NULL);
 436   if (frame == NULL)
 437     return;
 438
 439   m_frame.reset ((PyObject *) frame);
 440   m_tstate->frame = frame;
 441   m_saved_frame = frame->f_back;
 442   m_valid = true;
 443 }
 444 #endif
 445
 446 /* Helper for gdbpy_apply_val_pretty_printer that formats children of the
 447    printer, if any exist.  If is_py_none is true, then nothing has
 448    been printed by to_string, and format output accordingly. */
 449 static void
 450 print_children (PyObject *printer, const char *hint,
 451                 struct ui_file *stream, int recurse,
 452                 const struct value_print_options *options,
 453                 const struct language_defn *language,
 454                 int is_py_none)
 455 {
 456   int is_map, is_array, done_flag, pretty;
 457   unsigned int i;
 458
 459   if (! PyObject_HasAttr (printer, gdbpy_children_cst))
 460     return;
 461
 462   /* If we are printing a map or an array, we want some special
 463      formatting.  */
 464   is_map = hint && ! strcmp (hint, "map");
 465   is_array = hint && ! strcmp (hint, "array");
 466
 467   gdbpy_ref<> children (PyObject_CallMethodObjArgs (printer, gdbpy_children_cst,
 468                                                     NULL));
 469   if (children == NULL)
 470     {
 471       print_stack_unless_memory_error (stream);
 472       return;
 473     }
 474
 475   gdbpy_ref<> iter (PyObject_GetIter (children.get ()));
 476   if (iter == NULL)
 477     {
 478       print_stack_unless_memory_error (stream);
 479       return;
 480     }
 481
 482   /* Use the prettyformat_arrays option if we are printing an array,
 483      and the pretty option otherwise.  */
 484   if (is_array)
 485     pretty = options->prettyformat_arrays;
 486   else
 487     {
 488       if (options->prettyformat == Val_prettyformat)
 489         pretty = 1;
 490       else
 491         pretty = options->prettyformat_structs;
 492     }
 493
 494   /* Manufacture a dummy Python frame to work around Python 2.4 bug,
 495      where it insists on having a non-NULL tstate->frame when
 496      a generator is called.  */
 497 #ifndef IS_PY3K
 498   dummy_python_frame frame;
 499   if (frame.failed ())
 500     {
 501       gdbpy_print_stack ();
 502       return;
 503     }
 504 #endif
 505
 506   done_flag = 0;
 507   for (i = 0; i < options->print_max; ++i)
 508     {
 509       PyObject *py_v;
 510       const char *name;
 511
 512       gdbpy_ref<> item (PyIter_Next (iter.get ()));
 513       if (item == NULL)
 514         {
 515           if (PyErr_Occurred ())
 516             print_stack_unless_memory_error (stream);
 517           /* Set a flag so we can know whether we printed all the
 518              available elements.  */
 519           else
 520             done_flag = 1;
 521           break;
 522         }
 523
 524       if (! PyTuple_Check (item.get ()) || PyTuple_Size (item.get ()) != 2)
 525         {
 526           PyErr_SetString (PyExc_TypeError,
 527                            _("Result of children iterator not a tuple"
 528                              " of two elements."));
 529           gdbpy_print_stack ();
 530           continue;
 531         }
 532       if (! PyArg_ParseTuple (item.get (), "sO", &name, &py_v))
 533         {
 534           /* The user won't necessarily get a stack trace here, so provide
 535              more context.  */
 536           if (gdbpy_print_python_errors_p ())
 537             fprintf_unfiltered (gdb_stderr,
 538                                 _("Bad result from children iterator.\n"));
 539           gdbpy_print_stack ();
 540           continue;
 541         }
 542
 543       /* Print initial "{".  For other elements, there are three
 544          cases:
 545          1. Maps.  Print a "," after each value element.
 546          2. Arrays.  Always print a ",".
 547          3. Other.  Always print a ",".  */
 548       if (i == 0)
 549         {
 550          if (is_py_none)
 551            fputs_filtered ("{", stream);
 552          else
 553            fputs_filtered (" = {", stream);
 554        }
 555
 556       else if (! is_map || i % 2 == 0)
 557         fputs_filtered (pretty ? "," : ", ", stream);
 558
 559       /* In summary mode, we just want to print "= {...}" if there is
 560          a value.  */
 561       if (options->summary)
 562         {
 563           /* This increment tricks the post-loop logic to print what
 564              we want.  */
 565           ++i;
 566           /* Likewise.  */
 567           pretty = 0;
 568           break;
 569         }
 570
 571       if (! is_map || i % 2 == 0)
 572         {
 573           if (pretty)
 574             {
 575               fputs_filtered ("\n", stream);
 576               print_spaces_filtered (2 + 2 * recurse, stream);
 577             }
 578           else
 579             wrap_here (n_spaces (2 + 2 *recurse));
 580         }
 581
 582       if (is_map && i % 2 == 0)
 583         fputs_filtered ("[", stream);
 584       else if (is_array)
 585         {
 586           /* We print the index, not whatever the child method
 587              returned as the name.  */
 588           if (options->print_array_indexes)
 589             fprintf_filtered (stream, "[%d] = ", i);
 590         }
 591       else if (! is_map)
 592         {
 593           fputs_filtered (name, stream);
 594           fputs_filtered (" = ", stream);
 595         }
 596
 597       if (gdbpy_is_lazy_string (py_v))
 598         {
 599           CORE_ADDR addr;
 600           struct type *type;
 601           long length;
 602           gdb::unique_xmalloc_ptr<char> encoding;
 603           struct value_print_options local_opts = *options;
 604
 605           gdbpy_extract_lazy_string (py_v, &addr, &type, &length, &encoding);
 606
 607           local_opts.addressprint = 0;
 608           val_print_string (type, encoding.get (), addr, (int) length, stream,
 609                             &local_opts);
 610         }
 611       else if (gdbpy_is_string (py_v))
 612         {
 613           gdb::unique_xmalloc_ptr<char> output;
 614
 615           output = python_string_to_host_string (py_v);
 616           if (!output)
 617             gdbpy_print_stack ();
 618           else
 619             fputs_filtered (output.get (), stream);
 620         }
 621       else
 622         {
 623           struct value *value = convert_value_from_python (py_v);
 624
 625           if (value == NULL)
 626             {
 627               gdbpy_print_stack ();
 628               error (_("Error while executing Python code."));
 629             }
 630           else
 631             common_val_print (value, stream, recurse + 1, options, language);
 632         }
 633
 634       if (is_map && i % 2 == 0)
 635         fputs_filtered ("] = ", stream);
 636     }
 637
 638   if (i)
 639     {
 640       if (!done_flag)
 641         {
 642           if (pretty)
 643             {
 644               fputs_filtered ("\n", stream);
 645               print_spaces_filtered (2 + 2 * recurse, stream);
 646             }
 647           fputs_filtered ("...", stream);
 648         }
 649       if (pretty)
 650         {
 651           fputs_filtered ("\n", stream);
 652           print_spaces_filtered (2 * recurse, stream);
 653         }
 654       fputs_filtered ("}", stream);
 655     }
 656 }
 657
 658 enum ext_lang_rc
 659 gdbpy_apply_val_pretty_printer (const struct extension_language_defn *extlang,
 660                                 struct type *type,
 661                                 LONGEST embedded_offset, CORE_ADDR address,
 662                                 struct ui_file *stream, int recurse,
 663                                 struct value *val,
 664                                 const struct value_print_options *options,
 665                                 const struct language_defn *language)
 666 {
 667   struct gdbarch *gdbarch = get_type_arch (type);
 668   struct value *value;
 669   enum string_repr_result print_result;
 670
 671   if (value_lazy (val))
 672     value_fetch_lazy (val);
 673
 674   /* No pretty-printer support for unavailable values.  */
 675   if (!value_bytes_available (val, embedded_offset, TYPE_LENGTH (type)))
 676     return EXT_LANG_RC_NOP;
 677
 678   if (!gdb_python_initialized)
 679     return EXT_LANG_RC_NOP;
 680
 681   gdbpy_enter enter_py (gdbarch, language);
 682
 683   /* Instantiate the printer.  */
 684   value = value_from_component (val, type, embedded_offset);
 685
 686   gdbpy_ref<> val_obj (value_to_value_object (value));
 687   if (val_obj == NULL)
 688     {
 689       print_stack_unless_memory_error (stream);
 690       return EXT_LANG_RC_ERROR;
 691     }
 692
 693   /* Find the constructor.  */
 694   gdbpy_ref<> printer (find_pretty_printer (val_obj.get ()));
 695   if (printer == NULL)
 696     {
 697       print_stack_unless_memory_error (stream);
 698       return EXT_LANG_RC_ERROR;
 699     }
 700
 701   if (printer == Py_None)
 702     return EXT_LANG_RC_NOP;
 703
 704   /* If we are printing a map, we want some special formatting.  */
 705   gdb::unique_xmalloc_ptr<char> hint (gdbpy_get_display_hint (printer.get ()));
 706
 707   /* Print the section */
 708   print_result = print_string_repr (printer.get (), hint.get (), stream,
 709                                     recurse, options, language, gdbarch);
 710   if (print_result != string_repr_error)
 711     print_children (printer.get (), hint.get (), stream, recurse, options,
 712                     language, print_result == string_repr_none);
 713
 714   if (PyErr_Occurred ())
 715     print_stack_unless_memory_error (stream);
 716   return EXT_LANG_RC_OK;
 717 }
 718
 719
 720 /* Apply a pretty-printer for the varobj code.  PRINTER_OBJ is the
 721    print object.  It must have a 'to_string' method (but this is
 722    checked by varobj, not here) which takes no arguments and
 723    returns a string.  The printer will return a value and in the case
 724    of a Python string being returned, this function will return a
 725    PyObject containing the string.  For any other type, *REPLACEMENT is
 726    set to the replacement value and this function returns NULL.  On
 727    error, *REPLACEMENT is set to NULL and this function also returns
 728    NULL.  */
 729 gdbpy_ref<>
 730 apply_varobj_pretty_printer (PyObject *printer_obj,
 731                              struct value **replacement,
 732                              struct ui_file *stream)
 733 {
 734   *replacement = NULL;
 735   gdbpy_ref<> py_str = pretty_print_one_value (printer_obj, replacement);
 736
 737   if (*replacement == NULL && py_str == NULL)
 738     print_stack_unless_memory_error (stream);
 739
 740   return py_str;
 741 }
 742
 743 /* Find a pretty-printer object for the varobj module.  Returns a new
 744    reference to the object if successful; returns NULL if not.  VALUE
 745    is the value for which a printer tests to determine if it
 746    can pretty-print the value.  */
 747 PyObject *
 748 gdbpy_get_varobj_pretty_printer (struct value *value)
 749 {
 750   TRY
 751     {
 752       value = value_copy (value);
 753     }
 754   CATCH (except, RETURN_MASK_ALL)
 755     {
 756       GDB_PY_HANDLE_EXCEPTION (except);
 757     }
 758   END_CATCH
 759
 760   gdbpy_ref<> val_obj (value_to_value_object (value));
 761   if (val_obj == NULL)
 762     return NULL;
 763
 764   return find_pretty_printer (val_obj.get ());
 765 }
 766
 767 /* A Python function which wraps find_pretty_printer and instantiates
 768    the resulting class.  This accepts a Value argument and returns a
 769    pretty printer instance, or None.  This function is useful as an
 770    argument to the MI command -var-set-visualizer.  */
 771 PyObject *
 772 gdbpy_default_visualizer (PyObject *self, PyObject *args)
 773 {
 774   PyObject *val_obj;
 775   PyObject *cons;
 776   struct value *value;
 777
 778   if (! PyArg_ParseTuple (args, "O", &val_obj))
 779     return NULL;
 780   value = value_object_to_value (val_obj);
 781   if (! value)
 782     {
 783       PyErr_SetString (PyExc_TypeError,
 784                        _("Argument must be a gdb.Value."));
 785       return NULL;
 786     }
 787
 788   cons = find_pretty_printer (val_obj);
 789   return cons;
 790 }