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