gdb/python/py-prettyprint.c

   1 /* Python pretty-printing
   2
   3    Copyright (C) 2008-2017 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, NULL));
  77       if (printer == NULL)
  78         return NULL;
  79       else if (printer != Py_None)
  80         return printer.release ();
  81     }
  82
  83   Py_RETURN_NONE;
  84 }
  85
  86 /* Subroutine of find_pretty_printer to simplify it.
  87    Look for a pretty-printer to print VALUE in all objfiles.
  88    The result is NULL if there's an error and the search should be terminated.
  89    The result is Py_None, suitably inc-ref'd, if no pretty-printer was found.
  90    Otherwise the result is the pretty-printer function, suitably inc-ref'd.  */
  91
  92 static PyObject *
  93 find_pretty_printer_from_objfiles (PyObject *value)
  94 {
  95   struct objfile *obj;
  96
  97   ALL_OBJFILES (obj)
  98   {
  99     PyObject *objf = objfile_to_objfile_object (obj);
 100     if (!objf)
 101       {
 102         /* Ignore the error and continue.  */
 103         PyErr_Clear ();
 104         continue;
 105       }
 106
 107     gdbpy_ref pp_list (objfpy_get_printers (objf, NULL));
 108     gdbpy_ref function (search_pp_list (pp_list.get (), value));
 109
 110     /* If there is an error in any objfile list, abort the search and exit.  */
 111     if (function == NULL)
 112       return NULL;
 113
 114     if (function != Py_None)
 115       return function.release ();
 116   }
 117
 118   Py_RETURN_NONE;
 119 }
 120
 121 /* Subroutine of find_pretty_printer to simplify it.
 122    Look for a pretty-printer to print VALUE in the current program space.
 123    The result is NULL if there's an error and the search should be terminated.
 124    The result is Py_None, suitably inc-ref'd, if no pretty-printer was found.
 125    Otherwise the result is the pretty-printer function, suitably inc-ref'd.  */
 126
 127 static PyObject *
 128 find_pretty_printer_from_progspace (PyObject *value)
 129 {
 130   PyObject *obj = pspace_to_pspace_object (current_program_space);
 131
 132   if (!obj)
 133     return NULL;
 134   gdbpy_ref pp_list (pspy_get_printers (obj, NULL));
 135   return search_pp_list (pp_list.get (), value);
 136 }
 137
 138 /* Subroutine of find_pretty_printer to simplify it.
 139    Look for a pretty-printer to print VALUE in the gdb module.
 140    The result is NULL if there's an error and the search should be terminated.
 141    The result is Py_None, suitably inc-ref'd, if no pretty-printer was found.
 142    Otherwise the result is the pretty-printer function, suitably inc-ref'd.  */
 143
 144 static PyObject *
 145 find_pretty_printer_from_gdb (PyObject *value)
 146 {
 147   /* Fetch the global pretty printer list.  */
 148   if (gdb_python_module == NULL
 149       || ! PyObject_HasAttrString (gdb_python_module, "pretty_printers"))
 150     Py_RETURN_NONE;
 151   gdbpy_ref pp_list (PyObject_GetAttrString (gdb_python_module,
 152                                              "pretty_printers"));
 153   if (pp_list == NULL || ! PyList_Check (pp_list.get ()))
 154     Py_RETURN_NONE;
 155
 156   return search_pp_list (pp_list.get (), value);
 157 }
 158
 159 /* Find the pretty-printing constructor function for VALUE.  If no
 160    pretty-printer exists, return None.  If one exists, return a new
 161    reference.  On error, set the Python error and return NULL.  */
 162
 163 static PyObject *
 164 find_pretty_printer (PyObject *value)
 165 {
 166   /* Look at the pretty-printer list for each objfile
 167      in the current program-space.  */
 168   gdbpy_ref function (find_pretty_printer_from_objfiles (value));
 169   if (function == NULL || function != Py_None)
 170     return function.release ();
 171
 172   /* Look at the pretty-printer list for the current program-space.  */
 173   function.reset (find_pretty_printer_from_progspace (value));
 174   if (function == NULL || function != Py_None)
 175     return function.release ();
 176
 177   /* Look at the pretty-printer list in the gdb module.  */
 178   return find_pretty_printer_from_gdb (value);
 179 }
 180
 181 /* Pretty-print a single value, via the printer object PRINTER.
 182    If the function returns a string, a PyObject containing the string
 183    is returned.  If the function returns Py_NONE that means the pretty
 184    printer returned the Python None as a value.  Otherwise, if the
 185    function returns a value,  *OUT_VALUE is set to the value, and NULL
 186    is returned.  On error, *OUT_VALUE is set to NULL, NULL is
 187    returned, with a python exception set.  */
 188
 189 static PyObject *
 190 pretty_print_one_value (PyObject *printer, struct value **out_value)
 191 {
 192   PyObject *result = NULL;
 193
 194   *out_value = NULL;
 195   TRY
 196     {
 197       result = PyObject_CallMethodObjArgs (printer, gdbpy_to_string_cst, NULL);
 198       if (result)
 199         {
 200           if (! gdbpy_is_string (result) && ! gdbpy_is_lazy_string (result)
 201               && result != Py_None)
 202             {
 203               *out_value = convert_value_from_python (result);
 204               if (PyErr_Occurred ())
 205                 *out_value = NULL;
 206               Py_DECREF (result);
 207               result = NULL;
 208             }
 209         }
 210     }
 211   CATCH (except, RETURN_MASK_ALL)
 212     {
 213     }
 214   END_CATCH
 215
 216   return result;
 217 }
 218
 219 /* Return the display hint for the object printer, PRINTER.  Return
 220    NULL if there is no display_hint method, or if the method did not
 221    return a string.  On error, print stack trace and return NULL.  On
 222    success, return an xmalloc()d string.  */
 223 gdb::unique_xmalloc_ptr<char>
 224 gdbpy_get_display_hint (PyObject *printer)
 225 {
 226   gdb::unique_xmalloc_ptr<char> result;
 227
 228   if (! PyObject_HasAttr (printer, gdbpy_display_hint_cst))
 229     return NULL;
 230
 231   gdbpy_ref hint (PyObject_CallMethodObjArgs (printer, gdbpy_display_hint_cst,
 232                                               NULL));
 233   if (hint != NULL)
 234     {
 235       if (gdbpy_is_string (hint.get ()))
 236         {
 237           result = python_string_to_host_string (hint.get ());
 238           if (result == NULL)
 239             gdbpy_print_stack ();
 240         }
 241     }
 242   else
 243     gdbpy_print_stack ();
 244
 245   return result;
 246 }
 247
 248 /* A wrapper for gdbpy_print_stack that ignores MemoryError.  */
 249
 250 static void
 251 print_stack_unless_memory_error (struct ui_file *stream)
 252 {
 253   if (PyErr_ExceptionMatches (gdbpy_gdb_memory_error))
 254     {
 255       struct cleanup *cleanup;
 256       PyObject *type, *value, *trace;
 257
 258       PyErr_Fetch (&type, &value, &trace);
 259       cleanup = make_cleanup_py_decref (type);
 260       make_cleanup_py_decref (value);
 261       make_cleanup_py_decref (trace);
 262
 263       gdb::unique_xmalloc_ptr<char>
 264         msg (gdbpy_exception_to_string (type, value));
 265
 266       if (msg == NULL || *msg == '\0')
 267         fprintf_filtered (stream, _("<error reading variable>"));
 268       else
 269         fprintf_filtered (stream, _("<error reading variable: %s>"),
 270                           msg.get ());
 271
 272       do_cleanups (cleanup);
 273     }
 274   else
 275     gdbpy_print_stack ();
 276 }
 277
 278 /* Helper for gdbpy_apply_val_pretty_printer which calls to_string and
 279    formats the result.  */
 280
 281 static enum string_repr_result
 282 print_string_repr (PyObject *printer, const char *hint,
 283                    struct ui_file *stream, int recurse,
 284                    const struct value_print_options *options,
 285                    const struct language_defn *language,
 286                    struct gdbarch *gdbarch)
 287 {
 288   struct value *replacement = NULL;
 289   PyObject *py_str = NULL;
 290   enum string_repr_result result = string_repr_ok;
 291
 292   py_str = pretty_print_one_value (printer, &replacement);
 293   if (py_str)
 294     {
 295       struct cleanup *cleanup = make_cleanup_py_decref (py_str);
 296
 297       if (py_str == Py_None)
 298         result = string_repr_none;
 299       else if (gdbpy_is_lazy_string (py_str))
 300         {
 301           CORE_ADDR addr;
 302           long length;
 303           struct type *type;
 304           char *encoding = NULL;
 305           struct value_print_options local_opts = *options;
 306
 307           make_cleanup (free_current_contents, &encoding);
 308           gdbpy_extract_lazy_string (py_str, &addr, &type,
 309                                      &length, &encoding);
 310
 311           local_opts.addressprint = 0;
 312           val_print_string (type, encoding, addr, (int) length,
 313                             stream, &local_opts);
 314         }
 315       else
 316         {
 317           PyObject *string;
 318
 319           string = python_string_to_target_python_string (py_str);
 320           if (string)
 321             {
 322               char *output;
 323               long length;
 324               struct type *type;
 325
 326               make_cleanup_py_decref (string);
 327 #ifdef IS_PY3K
 328               output = PyBytes_AS_STRING (string);
 329               length = PyBytes_GET_SIZE (string);
 330 #else
 331               output = PyString_AsString (string);
 332               length = PyString_Size (string);
 333 #endif
 334               type = builtin_type (gdbarch)->builtin_char;
 335
 336               if (hint && !strcmp (hint, "string"))
 337                 LA_PRINT_STRING (stream, type, (gdb_byte *) output,
 338                                  length, NULL, 0, options);
 339               else
 340                 fputs_filtered (output, stream);
 341             }
 342           else
 343             {
 344               result = string_repr_error;
 345               print_stack_unless_memory_error (stream);
 346             }
 347         }
 348
 349       do_cleanups (cleanup);
 350     }
 351   else if (replacement)
 352     {
 353       struct value_print_options opts = *options;
 354
 355       opts.addressprint = 0;
 356       common_val_print (replacement, stream, recurse, &opts, language);
 357     }
 358   else
 359     {
 360       result = string_repr_error;
 361       print_stack_unless_memory_error (stream);
 362     }
 363
 364   return result;
 365 }
 366
 367 #ifndef IS_PY3K
 368 static void
 369 py_restore_tstate (void *p)
 370 {
 371   PyFrameObject *frame = (PyFrameObject *) p;
 372   PyThreadState *tstate = PyThreadState_GET ();
 373
 374   tstate->frame = frame;
 375 }
 376
 377 /* Create a dummy PyFrameObject, needed to work around
 378    a Python-2.4 bug with generators.  */
 379 static PyObject *
 380 push_dummy_python_frame (void)
 381 {
 382   PyObject *empty_string, *null_tuple, *globals;
 383   PyCodeObject *code;
 384   PyFrameObject *frame;
 385   PyThreadState *tstate;
 386
 387   empty_string = PyString_FromString ("");
 388   if (!empty_string)
 389     return NULL;
 390
 391   null_tuple = PyTuple_New (0);
 392   if (!null_tuple)
 393     {
 394       Py_DECREF (empty_string);
 395       return NULL;
 396     }
 397
 398   code = PyCode_New (0,                 /* argcount */
 399                      0,                 /* nlocals */
 400                      0,                 /* stacksize */
 401                      0,                 /* flags */
 402                      empty_string,      /* code */
 403                      null_tuple,        /* consts */
 404                      null_tuple,        /* names */
 405                      null_tuple,        /* varnames */
 406 #if PYTHON_API_VERSION >= 1010
 407                      null_tuple,        /* freevars */
 408                      null_tuple,        /* cellvars */
 409 #endif
 410                      empty_string,      /* filename */
 411                      empty_string,      /* name */
 412                      1,                 /* firstlineno */
 413                      empty_string       /* lnotab */
 414                     );
 415
 416   Py_DECREF (empty_string);
 417   Py_DECREF (null_tuple);
 418
 419   if (!code)
 420     return NULL;
 421
 422   globals = PyDict_New ();
 423   if (!globals)
 424     {
 425       Py_DECREF (code);
 426       return NULL;
 427     }
 428
 429   tstate = PyThreadState_GET ();
 430
 431   frame = PyFrame_New (tstate, code, globals, NULL);
 432
 433   Py_DECREF (globals);
 434   Py_DECREF (code);
 435
 436   if (!frame)
 437     return NULL;
 438
 439   tstate->frame = frame;
 440   make_cleanup (py_restore_tstate, frame->f_back);
 441   return (PyObject *) frame;
 442 }
 443 #endif
 444
 445 /* Helper for gdbpy_apply_val_pretty_printer that formats children of the
 446    printer, if any exist.  If is_py_none is true, then nothing has
 447    been printed by to_string, and format output accordingly. */
 448 static void
 449 print_children (PyObject *printer, const char *hint,
 450                 struct ui_file *stream, int recurse,
 451                 const struct value_print_options *options,
 452                 const struct language_defn *language,
 453                 int is_py_none)
 454 {
 455   int is_map, is_array, done_flag, pretty;
 456   unsigned int i;
 457   PyObject *children, *iter;
 458 #ifndef IS_PY3K
 459   PyObject *frame;
 460 #endif
 461   struct cleanup *cleanups;
 462
 463   if (! PyObject_HasAttr (printer, gdbpy_children_cst))
 464     return;
 465
 466   /* If we are printing a map or an array, we want some special
 467      formatting.  */
 468   is_map = hint && ! strcmp (hint, "map");
 469   is_array = hint && ! strcmp (hint, "array");
 470
 471   children = PyObject_CallMethodObjArgs (printer, gdbpy_children_cst,
 472                                          NULL);
 473   if (! children)
 474     {
 475       print_stack_unless_memory_error (stream);
 476       return;
 477     }
 478
 479   cleanups = make_cleanup_py_decref (children);
 480
 481   iter = PyObject_GetIter (children);
 482   if (!iter)
 483     {
 484       print_stack_unless_memory_error (stream);
 485       goto done;
 486     }
 487   make_cleanup_py_decref (iter);
 488
 489   /* Use the prettyformat_arrays option if we are printing an array,
 490      and the pretty option otherwise.  */
 491   if (is_array)
 492     pretty = options->prettyformat_arrays;
 493   else
 494     {
 495       if (options->prettyformat == Val_prettyformat)
 496         pretty = 1;
 497       else
 498         pretty = options->prettyformat_structs;
 499     }
 500
 501   /* Manufacture a dummy Python frame to work around Python 2.4 bug,
 502      where it insists on having a non-NULL tstate->frame when
 503      a generator is called.  */
 504 #ifndef IS_PY3K
 505   frame = push_dummy_python_frame ();
 506   if (!frame)
 507     {
 508       gdbpy_print_stack ();
 509       goto done;
 510     }
 511   make_cleanup_py_decref (frame);
 512 #endif
 513
 514   done_flag = 0;
 515   for (i = 0; i < options->print_max; ++i)
 516     {
 517       PyObject *py_v, *item = PyIter_Next (iter);
 518       const char *name;
 519       struct cleanup *inner_cleanup;
 520
 521       if (! item)
 522         {
 523           if (PyErr_Occurred ())
 524             print_stack_unless_memory_error (stream);
 525           /* Set a flag so we can know whether we printed all the
 526              available elements.  */
 527           else
 528             done_flag = 1;
 529           break;
 530         }
 531
 532       if (! PyTuple_Check (item) || PyTuple_Size (item) != 2)
 533         {
 534           PyErr_SetString (PyExc_TypeError,
 535                            _("Result of children iterator not a tuple"
 536                              " of two elements."));
 537           gdbpy_print_stack ();
 538           Py_DECREF (item);
 539           continue;
 540         }
 541       if (! PyArg_ParseTuple (item, "sO", &name, &py_v))
 542         {
 543           /* The user won't necessarily get a stack trace here, so provide
 544              more context.  */
 545           if (gdbpy_print_python_errors_p ())
 546             fprintf_unfiltered (gdb_stderr,
 547                                 _("Bad result from children iterator.\n"));
 548           gdbpy_print_stack ();
 549           Py_DECREF (item);
 550           continue;
 551         }
 552       inner_cleanup = make_cleanup_py_decref (item);
 553
 554       /* Print initial "{".  For other elements, there are three
 555          cases:
 556          1. Maps.  Print a "," after each value element.
 557          2. Arrays.  Always print a ",".
 558          3. Other.  Always print a ",".  */
 559       if (i == 0)
 560         {
 561          if (is_py_none)
 562            fputs_filtered ("{", stream);
 563          else
 564            fputs_filtered (" = {", stream);
 565        }
 566
 567       else if (! is_map || i % 2 == 0)
 568         fputs_filtered (pretty ? "," : ", ", stream);
 569
 570       /* In summary mode, we just want to print "= {...}" if there is
 571          a value.  */
 572       if (options->summary)
 573         {
 574           /* This increment tricks the post-loop logic to print what
 575              we want.  */
 576           ++i;
 577           /* Likewise.  */
 578           pretty = 0;
 579           break;
 580         }
 581
 582       if (! is_map || i % 2 == 0)
 583         {
 584           if (pretty)
 585             {
 586               fputs_filtered ("\n", stream);
 587               print_spaces_filtered (2 + 2 * recurse, stream);
 588             }
 589           else
 590             wrap_here (n_spaces (2 + 2 *recurse));
 591         }
 592
 593       if (is_map && i % 2 == 0)
 594         fputs_filtered ("[", stream);
 595       else if (is_array)
 596         {
 597           /* We print the index, not whatever the child method
 598              returned as the name.  */
 599           if (options->print_array_indexes)
 600             fprintf_filtered (stream, "[%d] = ", i);
 601         }
 602       else if (! is_map)
 603         {
 604           fputs_filtered (name, stream);
 605           fputs_filtered (" = ", stream);
 606         }
 607
 608       if (gdbpy_is_lazy_string (py_v))
 609         {
 610           CORE_ADDR addr;
 611           struct type *type;
 612           long length;
 613           char *encoding = NULL;
 614           struct value_print_options local_opts = *options;
 615
 616           make_cleanup (free_current_contents, &encoding);
 617           gdbpy_extract_lazy_string (py_v, &addr, &type, &length, &encoding);
 618
 619           local_opts.addressprint = 0;
 620           val_print_string (type, encoding, addr, (int) length, stream,
 621                             &local_opts);
 622         }
 623       else if (gdbpy_is_string (py_v))
 624         {
 625           gdb::unique_xmalloc_ptr<char> output;
 626
 627           output = python_string_to_host_string (py_v);
 628           if (!output)
 629             gdbpy_print_stack ();
 630           else
 631             fputs_filtered (output.get (), stream);
 632         }
 633       else
 634         {
 635           struct value *value = convert_value_from_python (py_v);
 636
 637           if (value == NULL)
 638             {
 639               gdbpy_print_stack ();
 640               error (_("Error while executing Python code."));
 641             }
 642           else
 643             common_val_print (value, stream, recurse + 1, options, language);
 644         }
 645
 646       if (is_map && i % 2 == 0)
 647         fputs_filtered ("] = ", stream);
 648
 649       do_cleanups (inner_cleanup);
 650     }
 651
 652   if (i)
 653     {
 654       if (!done_flag)
 655         {
 656           if (pretty)
 657             {
 658               fputs_filtered ("\n", stream);
 659               print_spaces_filtered (2 + 2 * recurse, stream);
 660             }
 661           fputs_filtered ("...", stream);
 662         }
 663       if (pretty)
 664         {
 665           fputs_filtered ("\n", stream);
 666           print_spaces_filtered (2 * recurse, stream);
 667         }
 668       fputs_filtered ("}", stream);
 669     }
 670
 671  done:
 672   do_cleanups (cleanups);
 673 }
 674
 675 enum ext_lang_rc
 676 gdbpy_apply_val_pretty_printer (const struct extension_language_defn *extlang,
 677                                 struct type *type,
 678                                 LONGEST embedded_offset, CORE_ADDR address,
 679                                 struct ui_file *stream, int recurse,
 680                                 struct value *val,
 681                                 const struct value_print_options *options,
 682                                 const struct language_defn *language)
 683 {
 684   struct gdbarch *gdbarch = get_type_arch (type);
 685   PyObject *printer = NULL;
 686   PyObject *val_obj = NULL;
 687   struct value *value;
 688   gdb::unique_xmalloc_ptr<char> hint;
 689   struct cleanup *cleanups;
 690   enum ext_lang_rc result = EXT_LANG_RC_NOP;
 691   enum string_repr_result print_result;
 692   const gdb_byte *valaddr = value_contents_for_printing (val);
 693
 694   /* No pretty-printer support for unavailable values.  */
 695   if (!value_bytes_available (val, embedded_offset, TYPE_LENGTH (type)))
 696     return EXT_LANG_RC_NOP;
 697
 698   if (!gdb_python_initialized)
 699     return EXT_LANG_RC_NOP;
 700
 701   cleanups = ensure_python_env (gdbarch, language);
 702
 703   /* Instantiate the printer.  */
 704   value = value_from_component (val, type, embedded_offset);
 705
 706   val_obj = value_to_value_object (value);
 707   if (! val_obj)
 708     {
 709       result = EXT_LANG_RC_ERROR;
 710       goto done;
 711     }
 712
 713   /* Find the constructor.  */
 714   printer = find_pretty_printer (val_obj);
 715   Py_DECREF (val_obj);
 716
 717   if (printer == NULL)
 718     {
 719       result = EXT_LANG_RC_ERROR;
 720       goto done;
 721     }
 722
 723   make_cleanup_py_decref (printer);
 724   if (printer == Py_None)
 725     {
 726       result = EXT_LANG_RC_NOP;
 727       goto done;
 728     }
 729
 730   /* If we are printing a map, we want some special formatting.  */
 731   hint = gdbpy_get_display_hint (printer);
 732
 733   /* Print the section */
 734   print_result = print_string_repr (printer, hint.get (), stream, recurse,
 735                                     options, language, gdbarch);
 736   if (print_result != string_repr_error)
 737     print_children (printer, hint.get (), stream, recurse, options, language,
 738                     print_result == string_repr_none);
 739
 740   result = EXT_LANG_RC_OK;
 741
 742  done:
 743   if (PyErr_Occurred ())
 744     print_stack_unless_memory_error (stream);
 745   do_cleanups (cleanups);
 746   return result;
 747 }
 748
 749
 750 /* Apply a pretty-printer for the varobj code.  PRINTER_OBJ is the
 751    print object.  It must have a 'to_string' method (but this is
 752    checked by varobj, not here) which takes no arguments and
 753    returns a string.  The printer will return a value and in the case
 754    of a Python string being returned, this function will return a
 755    PyObject containing the string.  For any other type, *REPLACEMENT is
 756    set to the replacement value and this function returns NULL.  On
 757    error, *REPLACEMENT is set to NULL and this function also returns
 758    NULL.  */
 759 PyObject *
 760 apply_varobj_pretty_printer (PyObject *printer_obj,
 761                              struct value **replacement,
 762                              struct ui_file *stream)
 763 {
 764   PyObject *py_str = NULL;
 765
 766   *replacement = NULL;
 767   py_str = pretty_print_one_value (printer_obj, replacement);
 768
 769   if (*replacement == NULL && py_str == NULL)
 770     print_stack_unless_memory_error (stream);
 771
 772   return py_str;
 773 }
 774
 775 /* Find a pretty-printer object for the varobj module.  Returns a new
 776    reference to the object if successful; returns NULL if not.  VALUE
 777    is the value for which a printer tests to determine if it
 778    can pretty-print the value.  */
 779 PyObject *
 780 gdbpy_get_varobj_pretty_printer (struct value *value)
 781 {
 782   TRY
 783     {
 784       value = value_copy (value);
 785     }
 786   CATCH (except, RETURN_MASK_ALL)
 787     {
 788       GDB_PY_HANDLE_EXCEPTION (except);
 789     }
 790   END_CATCH
 791
 792   gdbpy_ref val_obj (value_to_value_object (value));
 793   if (val_obj == NULL)
 794     return NULL;
 795
 796   return find_pretty_printer (val_obj.get ());
 797 }
 798
 799 /* A Python function which wraps find_pretty_printer and instantiates
 800    the resulting class.  This accepts a Value argument and returns a
 801    pretty printer instance, or None.  This function is useful as an
 802    argument to the MI command -var-set-visualizer.  */
 803 PyObject *
 804 gdbpy_default_visualizer (PyObject *self, PyObject *args)
 805 {
 806   PyObject *val_obj;
 807   PyObject *cons;
 808   struct value *value;
 809
 810   if (! PyArg_ParseTuple (args, "O", &val_obj))
 811     return NULL;
 812   value = value_object_to_value (val_obj);
 813   if (! value)
 814     {
 815       PyErr_SetString (PyExc_TypeError,
 816                        _("Argument must be a gdb.Value."));
 817       return NULL;
 818     }
 819
 820   cons = find_pretty_printer (val_obj);
 821   return cons;
 822 }