gdb/python/py-prettyprint.c

   1 /* Python pretty-printing
   2
   3    Copyright (C) 2008-2019 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 gdbpy_ref<>
  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;
  82     }
  83
  84   return gdbpy_ref<>::new_reference (Py_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 gdbpy_ref<>
 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 gdbpy_ref<>
 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     return gdbpy_ref<>::new_reference (Py_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     return gdbpy_ref<>::new_reference (Py_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 gdbpy_ref<>
 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;
 172
 173   /* Look at the pretty-printer list for the current program-space.  */
 174   function = find_pretty_printer_from_progspace (value);
 175   if (function == NULL || function != Py_None)
 176     return function;
 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       gdbpy_err_fetch fetched_error;
 263       gdb::unique_xmalloc_ptr<char> msg = fetched_error.to_string ();
 264
 265       if (msg == NULL || *msg == '\0')
 266         fprintf_filtered (stream, _("<error reading variable>"));
 267       else
 268         fprintf_filtered (stream, _("<error reading variable: %s>"),
 269                           msg.get ());
 270     }
 271   else
 272     gdbpy_print_stack ();
 273 }
 274
 275 /* Helper for gdbpy_apply_val_pretty_printer which calls to_string and
 276    formats the result.  */
 277
 278 static enum string_repr_result
 279 print_string_repr (PyObject *printer, const char *hint,
 280                    struct ui_file *stream, int recurse,
 281                    const struct value_print_options *options,
 282                    const struct language_defn *language,
 283                    struct gdbarch *gdbarch)
 284 {
 285   struct value *replacement = NULL;
 286   enum string_repr_result result = string_repr_ok;
 287
 288   gdbpy_ref<> py_str = pretty_print_one_value (printer, &replacement);
 289   if (py_str != NULL)
 290     {
 291       if (py_str == Py_None)
 292         result = string_repr_none;
 293       else if (gdbpy_is_lazy_string (py_str.get ()))
 294         {
 295           CORE_ADDR addr;
 296           long length;
 297           struct type *type;
 298           gdb::unique_xmalloc_ptr<char> encoding;
 299           struct value_print_options local_opts = *options;
 300
 301           gdbpy_extract_lazy_string (py_str.get (), &addr, &type,
 302                                      &length, &encoding);
 303
 304           local_opts.addressprint = 0;
 305           val_print_string (type, encoding.get (), addr, (int) length,
 306                             stream, &local_opts);
 307         }
 308       else
 309         {
 310           gdbpy_ref<> string
 311             = python_string_to_target_python_string (py_str.get ());
 312           if (string != NULL)
 313             {
 314               char *output;
 315               long length;
 316               struct type *type;
 317
 318 #ifdef IS_PY3K
 319               output = PyBytes_AS_STRING (string.get ());
 320               length = PyBytes_GET_SIZE (string.get ());
 321 #else
 322               output = PyString_AsString (string.get ());
 323               length = PyString_Size (string.get ());
 324 #endif
 325               type = builtin_type (gdbarch)->builtin_char;
 326
 327               if (hint && !strcmp (hint, "string"))
 328                 LA_PRINT_STRING (stream, type, (gdb_byte *) output,
 329                                  length, NULL, 0, options);
 330               else
 331                 fputs_filtered (output, stream);
 332             }
 333           else
 334             {
 335               result = string_repr_error;
 336               print_stack_unless_memory_error (stream);
 337             }
 338         }
 339     }
 340   else if (replacement)
 341     {
 342       struct value_print_options opts = *options;
 343
 344       opts.addressprint = 0;
 345       common_val_print (replacement, stream, recurse, &opts, language);
 346     }
 347   else
 348     {
 349       result = string_repr_error;
 350       print_stack_unless_memory_error (stream);
 351     }
 352
 353   return result;
 354 }
 355
 356 #ifndef IS_PY3K
 357
 358 /* Create a dummy PyFrameObject, needed to work around
 359    a Python-2.4 bug with generators.  */
 360 class dummy_python_frame
 361 {
 362  public:
 363
 364   dummy_python_frame ();
 365
 366   ~dummy_python_frame ()
 367   {
 368     if (m_valid)
 369       m_tstate->frame = m_saved_frame;
 370   }
 371
 372   bool failed () const
 373   {
 374     return !m_valid;
 375   }
 376
 377  private:
 378
 379   bool m_valid;
 380   PyFrameObject *m_saved_frame;
 381   gdbpy_ref<> m_frame;
 382   PyThreadState *m_tstate;
 383 };
 384
 385 dummy_python_frame::dummy_python_frame ()
 386 : m_valid (false),
 387   m_saved_frame (NULL),
 388   m_tstate (NULL)
 389 {
 390   PyCodeObject *code;
 391   PyFrameObject *frame;
 392
 393   gdbpy_ref<> empty_string (PyString_FromString (""));
 394   if (empty_string == NULL)
 395     return;
 396
 397   gdbpy_ref<> null_tuple (PyTuple_New (0));
 398   if (null_tuple == NULL)
 399     return;
 400
 401   code = PyCode_New (0,                   /* argcount */
 402                      0,                   /* locals */
 403                      0,                   /* stacksize */
 404                      0,                   /* flags */
 405                      empty_string.get (), /* code */
 406                      null_tuple.get (),   /* consts */
 407                      null_tuple.get (),   /* names */
 408                      null_tuple.get (),   /* varnames */
 409 #if PYTHON_API_VERSION >= 1010
 410                      null_tuple.get (),   /* freevars */
 411                      null_tuple.get (),   /* cellvars */
 412 #endif
 413                      empty_string.get (), /* filename */
 414                      empty_string.get (), /* name */
 415                      1,                   /* firstlineno */
 416                      empty_string.get ()  /* lnotab */
 417                      );
 418   if (code == NULL)
 419     return;
 420   gdbpy_ref<> code_holder ((PyObject *) code);
 421
 422   gdbpy_ref<> globals (PyDict_New ());
 423   if (globals == NULL)
 424     return;
 425
 426   m_tstate = PyThreadState_GET ();
 427   frame = PyFrame_New (m_tstate, code, globals.get (), NULL);
 428   if (frame == NULL)
 429     return;
 430
 431   m_frame.reset ((PyObject *) frame);
 432   m_tstate->frame = frame;
 433   m_saved_frame = frame->f_back;
 434   m_valid = true;
 435 }
 436 #endif
 437
 438 /* Helper for gdbpy_apply_val_pretty_printer that formats children of the
 439    printer, if any exist.  If is_py_none is true, then nothing has
 440    been printed by to_string, and format output accordingly. */
 441 static void
 442 print_children (PyObject *printer, const char *hint,
 443                 struct ui_file *stream, int recurse,
 444                 const struct value_print_options *options,
 445                 const struct language_defn *language,
 446                 int is_py_none)
 447 {
 448   int is_map, is_array, done_flag, pretty;
 449   unsigned int i;
 450
 451   if (! PyObject_HasAttr (printer, gdbpy_children_cst))
 452     return;
 453
 454   /* If we are printing a map or an array, we want some special
 455      formatting.  */
 456   is_map = hint && ! strcmp (hint, "map");
 457   is_array = hint && ! strcmp (hint, "array");
 458
 459   gdbpy_ref<> children (PyObject_CallMethodObjArgs (printer, gdbpy_children_cst,
 460                                                     NULL));
 461   if (children == NULL)
 462     {
 463       print_stack_unless_memory_error (stream);
 464       return;
 465     }
 466
 467   gdbpy_ref<> iter (PyObject_GetIter (children.get ()));
 468   if (iter == NULL)
 469     {
 470       print_stack_unless_memory_error (stream);
 471       return;
 472     }
 473
 474   /* Use the prettyformat_arrays option if we are printing an array,
 475      and the pretty option otherwise.  */
 476   if (is_array)
 477     pretty = options->prettyformat_arrays;
 478   else
 479     {
 480       if (options->prettyformat == Val_prettyformat)
 481         pretty = 1;
 482       else
 483         pretty = options->prettyformat_structs;
 484     }
 485
 486   /* Manufacture a dummy Python frame to work around Python 2.4 bug,
 487      where it insists on having a non-NULL tstate->frame when
 488      a generator is called.  */
 489 #ifndef IS_PY3K
 490   dummy_python_frame frame;
 491   if (frame.failed ())
 492     {
 493       gdbpy_print_stack ();
 494       return;
 495     }
 496 #endif
 497
 498   done_flag = 0;
 499   for (i = 0; i < options->print_max; ++i)
 500     {
 501       PyObject *py_v;
 502       const char *name;
 503
 504       gdbpy_ref<> item (PyIter_Next (iter.get ()));
 505       if (item == NULL)
 506         {
 507           if (PyErr_Occurred ())
 508             print_stack_unless_memory_error (stream);
 509           /* Set a flag so we can know whether we printed all the
 510              available elements.  */
 511           else
 512             done_flag = 1;
 513           break;
 514         }
 515
 516       if (! PyTuple_Check (item.get ()) || PyTuple_Size (item.get ()) != 2)
 517         {
 518           PyErr_SetString (PyExc_TypeError,
 519                            _("Result of children iterator not a tuple"
 520                              " of two elements."));
 521           gdbpy_print_stack ();
 522           continue;
 523         }
 524       if (! PyArg_ParseTuple (item.get (), "sO", &name, &py_v))
 525         {
 526           /* The user won't necessarily get a stack trace here, so provide
 527              more context.  */
 528           if (gdbpy_print_python_errors_p ())
 529             fprintf_unfiltered (gdb_stderr,
 530                                 _("Bad result from children iterator.\n"));
 531           gdbpy_print_stack ();
 532           continue;
 533         }
 534
 535       /* Print initial "{".  For other elements, there are three
 536          cases:
 537          1. Maps.  Print a "," after each value element.
 538          2. Arrays.  Always print a ",".
 539          3. Other.  Always print a ",".  */
 540       if (i == 0)
 541         {
 542          if (is_py_none)
 543            fputs_filtered ("{", stream);
 544          else
 545            fputs_filtered (" = {", stream);
 546        }
 547
 548       else if (! is_map || i % 2 == 0)
 549         fputs_filtered (pretty ? "," : ", ", stream);
 550
 551       /* In summary mode, we just want to print "= {...}" if there is
 552          a value.  */
 553       if (options->summary)
 554         {
 555           /* This increment tricks the post-loop logic to print what
 556              we want.  */
 557           ++i;
 558           /* Likewise.  */
 559           pretty = 0;
 560           break;
 561         }
 562
 563       if (! is_map || i % 2 == 0)
 564         {
 565           if (pretty)
 566             {
 567               fputs_filtered ("\n", stream);
 568               print_spaces_filtered (2 + 2 * recurse, stream);
 569             }
 570           else
 571             wrap_here (n_spaces (2 + 2 *recurse));
 572         }
 573
 574       if (is_map && i % 2 == 0)
 575         fputs_filtered ("[", stream);
 576       else if (is_array)
 577         {
 578           /* We print the index, not whatever the child method
 579              returned as the name.  */
 580           if (options->print_array_indexes)
 581             fprintf_filtered (stream, "[%d] = ", i);
 582         }
 583       else if (! is_map)
 584         {
 585           fputs_filtered (name, stream);
 586           fputs_filtered (" = ", stream);
 587         }
 588
 589       if (gdbpy_is_lazy_string (py_v))
 590         {
 591           CORE_ADDR addr;
 592           struct type *type;
 593           long length;
 594           gdb::unique_xmalloc_ptr<char> encoding;
 595           struct value_print_options local_opts = *options;
 596
 597           gdbpy_extract_lazy_string (py_v, &addr, &type, &length, &encoding);
 598
 599           local_opts.addressprint = 0;
 600           val_print_string (type, encoding.get (), addr, (int) length, stream,
 601                             &local_opts);
 602         }
 603       else if (gdbpy_is_string (py_v))
 604         {
 605           gdb::unique_xmalloc_ptr<char> output;
 606
 607           output = python_string_to_host_string (py_v);
 608           if (!output)
 609             gdbpy_print_stack ();
 610           else
 611             fputs_filtered (output.get (), stream);
 612         }
 613       else
 614         {
 615           struct value *value = convert_value_from_python (py_v);
 616
 617           if (value == NULL)
 618             {
 619               gdbpy_print_stack ();
 620               error (_("Error while executing Python code."));
 621             }
 622           else
 623             common_val_print (value, stream, recurse + 1, options, language);
 624         }
 625
 626       if (is_map && i % 2 == 0)
 627         fputs_filtered ("] = ", stream);
 628     }
 629
 630   if (i)
 631     {
 632       if (!done_flag)
 633         {
 634           if (pretty)
 635             {
 636               fputs_filtered ("\n", stream);
 637               print_spaces_filtered (2 + 2 * recurse, stream);
 638             }
 639           fputs_filtered ("...", stream);
 640         }
 641       if (pretty)
 642         {
 643           fputs_filtered ("\n", stream);
 644           print_spaces_filtered (2 * recurse, stream);
 645         }
 646       fputs_filtered ("}", stream);
 647     }
 648 }
 649
 650 enum ext_lang_rc
 651 gdbpy_apply_val_pretty_printer (const struct extension_language_defn *extlang,
 652                                 struct type *type,
 653                                 LONGEST embedded_offset, CORE_ADDR address,
 654                                 struct ui_file *stream, int recurse,
 655                                 struct value *val,
 656                                 const struct value_print_options *options,
 657                                 const struct language_defn *language)
 658 {
 659   struct gdbarch *gdbarch = get_type_arch (type);
 660   struct value *value;
 661   enum string_repr_result print_result;
 662
 663   if (value_lazy (val))
 664     value_fetch_lazy (val);
 665
 666   /* No pretty-printer support for unavailable values.  */
 667   if (!value_bytes_available (val, embedded_offset, TYPE_LENGTH (type)))
 668     return EXT_LANG_RC_NOP;
 669
 670   if (!gdb_python_initialized)
 671     return EXT_LANG_RC_NOP;
 672
 673   gdbpy_enter enter_py (gdbarch, language);
 674
 675   /* Instantiate the printer.  */
 676   value = value_from_component (val, type, embedded_offset);
 677
 678   gdbpy_ref<> val_obj (value_to_value_object (value));
 679   if (val_obj == NULL)
 680     {
 681       print_stack_unless_memory_error (stream);
 682       return EXT_LANG_RC_ERROR;
 683     }
 684
 685   /* Find the constructor.  */
 686   gdbpy_ref<> printer (find_pretty_printer (val_obj.get ()));
 687   if (printer == NULL)
 688     {
 689       print_stack_unless_memory_error (stream);
 690       return EXT_LANG_RC_ERROR;
 691     }
 692
 693   if (printer == Py_None)
 694     return EXT_LANG_RC_NOP;
 695
 696   /* If we are printing a map, we want some special formatting.  */
 697   gdb::unique_xmalloc_ptr<char> hint (gdbpy_get_display_hint (printer.get ()));
 698
 699   /* Print the section */
 700   print_result = print_string_repr (printer.get (), hint.get (), stream,
 701                                     recurse, options, language, gdbarch);
 702   if (print_result != string_repr_error)
 703     print_children (printer.get (), hint.get (), stream, recurse, options,
 704                     language, print_result == string_repr_none);
 705
 706   if (PyErr_Occurred ())
 707     print_stack_unless_memory_error (stream);
 708   return EXT_LANG_RC_OK;
 709 }
 710
 711
 712 /* Apply a pretty-printer for the varobj code.  PRINTER_OBJ is the
 713    print object.  It must have a 'to_string' method (but this is
 714    checked by varobj, not here) which takes no arguments and
 715    returns a string.  The printer will return a value and in the case
 716    of a Python string being returned, this function will return a
 717    PyObject containing the string.  For any other type, *REPLACEMENT is
 718    set to the replacement value and this function returns NULL.  On
 719    error, *REPLACEMENT is set to NULL and this function also returns
 720    NULL.  */
 721 gdbpy_ref<>
 722 apply_varobj_pretty_printer (PyObject *printer_obj,
 723                              struct value **replacement,
 724                              struct ui_file *stream)
 725 {
 726   *replacement = NULL;
 727   gdbpy_ref<> py_str = pretty_print_one_value (printer_obj, replacement);
 728
 729   if (*replacement == NULL && py_str == NULL)
 730     print_stack_unless_memory_error (stream);
 731
 732   return py_str;
 733 }
 734
 735 /* Find a pretty-printer object for the varobj module.  Returns a new
 736    reference to the object if successful; returns NULL if not.  VALUE
 737    is the value for which a printer tests to determine if it
 738    can pretty-print the value.  */
 739 gdbpy_ref<>
 740 gdbpy_get_varobj_pretty_printer (struct value *value)
 741 {
 742   TRY
 743     {
 744       value = value_copy (value);
 745     }
 746   CATCH (except, RETURN_MASK_ALL)
 747     {
 748       GDB_PY_HANDLE_EXCEPTION (except);
 749     }
 750   END_CATCH
 751
 752   gdbpy_ref<> val_obj (value_to_value_object (value));
 753   if (val_obj == NULL)
 754     return NULL;
 755
 756   return find_pretty_printer (val_obj.get ());
 757 }
 758
 759 /* A Python function which wraps find_pretty_printer and instantiates
 760    the resulting class.  This accepts a Value argument and returns a
 761    pretty printer instance, or None.  This function is useful as an
 762    argument to the MI command -var-set-visualizer.  */
 763 PyObject *
 764 gdbpy_default_visualizer (PyObject *self, PyObject *args)
 765 {
 766   PyObject *val_obj;
 767   struct value *value;
 768
 769   if (! PyArg_ParseTuple (args, "O", &val_obj))
 770     return NULL;
 771   value = value_object_to_value (val_obj);
 772   if (! value)
 773     {
 774       PyErr_SetString (PyExc_TypeError,
 775                        _("Argument must be a gdb.Value."));
 776       return NULL;
 777     }
 778
 779   return find_pretty_printer (val_obj).release ();
 780 }