gcc/spellcheck.c

   1 /* Find near-matches for strings.
   2    Copyright (C) 2015-2021 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify it under
   7 the terms of the GNU General Public License as published by the Free
   8 Software Foundation; either version 3, or (at your option) any later
   9 version.
  10
  11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14 for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GCC; see the file COPYING3.  If not see
  18 <http://www.gnu.org/licenses/>.  */
  19
  20 #include "config.h"
  21 #include "system.h"
  22 #include "coretypes.h"
  23 #include "tm.h"
  24 #include "tree.h"
  25 #include "spellcheck.h"
  26 #include "selftest.h"
  27
  28 /* Cost of a case transformation.  */
  29 #define CASE_COST 1
  30
  31 /* Cost of another kind of edit.  */
  32 #define BASE_COST 2
  33
  34 /* Get the edit distance between the two strings: the minimal
  35    number of edits that are needed to change one string into another,
  36    where edits can be one-character insertions, removals, or substitutions,
  37    or transpositions of two adjacent characters (counting as one "edit").
  38
  39    This implementation uses a modified variant of the Wagner-Fischer
  40    algorithm for the Damerau-Levenshtein distance; specifically, the
  41    "optimal string alignment distance" or "restricted edit distance"
  42    variant.  This implementation has been further modified to take
  43    case into account.  */
  44
  45 edit_distance_t
  46 get_edit_distance (const char *s, int len_s,
  47                    const char *t, int len_t)
  48 {
  49   const bool debug = false;
  50
  51   if (debug)
  52     {
  53       printf ("s: \"%s\" (len_s=%i)\n", s, len_s);
  54       printf ("t: \"%s\" (len_t=%i)\n", t, len_t);
  55     }
  56
  57   if (len_s == 0)
  58     return BASE_COST * len_t;
  59   if (len_t == 0)
  60     return BASE_COST * len_s;
  61
  62   /* We effectively build a matrix where each (i, j) contains the
  63      distance between the prefix strings s[0:j] and t[0:i].
  64      Rather than actually build an (len_t + 1) * (len_s + 1) matrix,
  65      we simply keep track of the last two rows, v_one_ago and v_two_ago,
  66      and a new row, v_next, which avoids an (len_t + 1) * (len_s + 1)
  67      allocation and memory accesses in favor of three (len_s + 1)
  68      allocations.  These could potentially be
  69      statically-allocated if we impose a maximum length on the
  70      strings of interest.  */
  71   edit_distance_t *v_two_ago = new edit_distance_t[len_s + 1];
  72   edit_distance_t *v_one_ago = new edit_distance_t[len_s + 1];
  73   edit_distance_t *v_next = new edit_distance_t[len_s + 1];
  74
  75   /* The first row is for the case of an empty target string, which
  76      we can reach by deleting every character in the source string.  */
  77   for (int i = 0; i < len_s + 1; i++)
  78     v_one_ago[i] = i * BASE_COST;
  79
  80   /* Build successive rows.  */
  81   for (int i = 0; i < len_t; i++)
  82     {
  83       if (debug)
  84         {
  85           printf ("i:%i v_one_ago = ", i);
  86           for (int j = 0; j < len_s + 1; j++)
  87             printf ("%i ", v_one_ago[j]);
  88           printf ("\n");
  89         }
  90
  91       /* The initial column is for the case of an empty source string; we
  92          can reach prefixes of the target string of length i
  93          by inserting i characters.  */
  94       v_next[0] = (i + 1) * BASE_COST;
  95
  96       /* Build the rest of the row by considering neighbors to
  97          the north, west and northwest.  */
  98       for (int j = 0; j < len_s; j++)
  99         {
 100           edit_distance_t cost;
 101
 102           if (s[j] == t[i])
 103             cost = 0;
 104           else if (TOLOWER (s[j]) == TOLOWER (t[i]))
 105             cost = CASE_COST;
 106           else
 107             cost = BASE_COST;
 108           edit_distance_t deletion     = v_next[j] + BASE_COST;
 109           edit_distance_t insertion    = v_one_ago[j + 1] + BASE_COST;
 110           edit_distance_t substitution = v_one_ago[j] + cost;
 111           edit_distance_t cheapest = MIN (deletion, insertion);
 112           cheapest = MIN (cheapest, substitution);
 113           if (i > 0 && j > 0 && s[j] == t[i - 1] && s[j - 1] == t[i])
 114             {
 115               edit_distance_t transposition = v_two_ago[j - 1] + BASE_COST;
 116               cheapest = MIN (cheapest, transposition);
 117             }
 118           v_next[j + 1] = cheapest;
 119         }
 120
 121       /* Prepare to move on to next row.  */
 122       for (int j = 0; j < len_s + 1; j++)
 123         {
 124           v_two_ago[j] = v_one_ago[j];
 125           v_one_ago[j] = v_next[j];
 126         }
 127     }
 128
 129   if (debug)
 130     {
 131       printf ("final v_next = ");
 132       for (int j = 0; j < len_s + 1; j++)
 133         printf ("%i ", v_next[j]);
 134       printf ("\n");
 135     }
 136
 137   edit_distance_t result = v_next[len_s];
 138   delete[] v_two_ago;
 139   delete[] v_one_ago;
 140   delete[] v_next;
 141   return result;
 142 }
 143
 144 /* Get the edit distance between two nil-terminated strings.  */
 145
 146 edit_distance_t
 147 get_edit_distance (const char *s, const char *t)
 148 {
 149   return get_edit_distance (s, strlen (s), t, strlen (t));
 150 }
 151
 152 /* Given TARGET, a non-NULL string, and CANDIDATES, a non-NULL ptr to
 153    an autovec of non-NULL strings, determine which element within
 154    CANDIDATES has the lowest edit distance to TARGET.  If there are
 155    multiple elements with the same minimal distance, the first in the
 156    vector wins.
 157
 158    If more than half of the letters were misspelled, the suggestion is
 159    likely to be meaningless, so return NULL for this case.  */
 160
 161 const char *
 162 find_closest_string (const char *target,
 163                      const auto_vec<const char *> *candidates)
 164 {
 165   gcc_assert (target);
 166   gcc_assert (candidates);
 167
 168   int i;
 169   const char *candidate;
 170   best_match<const char *, const char *> bm (target);
 171   FOR_EACH_VEC_ELT (*candidates, i, candidate)
 172     {
 173       gcc_assert (candidate);
 174       bm.consider (candidate);
 175     }
 176
 177   return bm.get_best_meaningful_candidate ();
 178 }
 179
 180 /* Generate the maximum edit distance for which we consider a suggestion
 181    to be meaningful, given a goal of length GOAL_LEN and a candidate of
 182    length CANDIDATE_LEN.
 183
 184    This is a third of the length of the candidate or of the goal,
 185    whichever is bigger.  */
 186
 187 edit_distance_t
 188 get_edit_distance_cutoff (size_t goal_len, size_t candidate_len)
 189 {
 190   size_t max_length = MAX (goal_len, candidate_len);
 191   size_t min_length = MIN (goal_len, candidate_len);
 192
 193   gcc_assert (max_length >= min_length);
 194
 195   /* Special case: don't offer suggestions for a pair of
 196      length == 1 strings (or empty strings).  */
 197   if (max_length <= 1)
 198     return 0;
 199
 200   /* If the lengths are close, then round down.  */
 201   if (max_length - min_length <= 1)
 202     /* ...but allow an edit distance of at least 1.  */
 203     return BASE_COST * MAX (max_length / 3, 1);
 204
 205   /* Otherwise, round up (thus giving a little extra leeway to some cases
 206      involving insertions/deletions).  */
 207   return BASE_COST * (max_length + 2) / 3;
 208 }
 209
 210 #if CHECKING_P
 211
 212 namespace selftest {
 213
 214 /* Selftests.  */
 215
 216 /* Verify that get_edit_distance (A, B) equals the expected value.  */
 217
 218 static void
 219 test_get_edit_distance_one_way (const char *a, const char *b,
 220                                 edit_distance_t expected)
 221 {
 222   edit_distance_t actual = get_edit_distance (a, b);
 223   ASSERT_EQ (actual, expected);
 224 }
 225
 226 /* Verify that both
 227      get_edit_distance (A, B)
 228    and
 229      get_edit_distance (B, A)
 230    equal the expected value, to ensure that the function is symmetric.  */
 231
 232 static void
 233 test_get_edit_distance_both_ways (const char *a, const char *b,
 234                              edit_distance_t expected)
 235 {
 236   test_get_edit_distance_one_way (a, b, expected);
 237   test_get_edit_distance_one_way (b, a, expected);
 238 }
 239
 240 /* Verify get_edit_distance for a variety of pairs of pre-canned
 241    inputs, comparing against known-good values.  */
 242
 243 static void
 244 test_edit_distances ()
 245 {
 246   test_get_edit_distance_both_ways ("", "nonempty",
 247                                     BASE_COST * strlen ("nonempty"));
 248   test_get_edit_distance_both_ways ("saturday", "sunday",
 249                                     BASE_COST * 3);
 250   test_get_edit_distance_both_ways ("foo", "m_foo", BASE_COST * 2);
 251   test_get_edit_distance_both_ways ("hello_world", "HelloWorld", 4);
 252   test_get_edit_distance_both_ways
 253     ("the quick brown fox jumps over the lazy dog", "dog", BASE_COST * 40);
 254   test_get_edit_distance_both_ways
 255     ("the quick brown fox jumps over the lazy dog",
 256      "the quick brown dog jumps over the lazy fox",
 257      BASE_COST * 4);
 258   test_get_edit_distance_both_ways
 259     ("Lorem ipsum dolor sit amet, consectetur adipiscing elit,",
 260      "All your base are belong to us",
 261      BASE_COST * 44);
 262   test_get_edit_distance_both_ways ("foo", "FOO", 3);
 263   test_get_edit_distance_both_ways ("fee", "deed", BASE_COST * 2);
 264   test_get_edit_distance_both_ways ("coorzd1", "coordx1", BASE_COST * 2);
 265   test_get_edit_distance_both_ways ("assert", "sqrt", BASE_COST * 3);
 266   test_get_edit_distance_both_ways ("PATH_MAX", "INT8_MAX", BASE_COST * 3);
 267   test_get_edit_distance_both_ways ("time", "nice", BASE_COST * 2);
 268   test_get_edit_distance_both_ways ("bar", "carg", BASE_COST * 2);
 269   test_get_edit_distance_both_ways ("gtk_widget_show_all",
 270                                     "GtkWidgetShowAll", 10);
 271   test_get_edit_distance_both_ways ("m_bar", "bar", BASE_COST * 2);
 272   test_get_edit_distance_both_ways ("MACRO", "MACRAME", BASE_COST * 3);
 273   test_get_edit_distance_both_ways ("ab", "ac", BASE_COST * 1);
 274   test_get_edit_distance_both_ways ("ab", "a", BASE_COST * 1);
 275   test_get_edit_distance_both_ways ("a", "b", BASE_COST * 1);
 276   test_get_edit_distance_both_ways ("nanl", "name", BASE_COST * 2);
 277   test_get_edit_distance_both_ways ("char", "bar", BASE_COST * 2);
 278   test_get_edit_distance_both_ways ("-optimize", "fsanitize", BASE_COST * 5);
 279   test_get_edit_distance_both_ways ("__DATE__", "__i386__", BASE_COST * 4);
 280
 281   /* Examples where transposition helps.  */
 282   test_get_edit_distance_both_ways ("ab", "ba", BASE_COST * 1);
 283   test_get_edit_distance_both_ways ("ba", "abc", BASE_COST * 2);
 284   test_get_edit_distance_both_ways ("coorzd1", "coordz1", BASE_COST * 1);
 285   test_get_edit_distance_both_ways ("abcdefghijklmnopqrstuvwxyz",
 286                                     "bacdefghijklmnopqrstuvwxzy",
 287                                     BASE_COST * 2);
 288   test_get_edit_distance_both_ways ("saturday", "sundya", BASE_COST * 4);
 289   test_get_edit_distance_both_ways ("signed", "singed", BASE_COST * 1);
 290 }
 291
 292 /* Subroutine of test_get_edit_distance_cutoff, for emulating the
 293    spellchecking cutoff in up to GCC 8.  */
 294
 295 static edit_distance_t
 296 get_old_cutoff (size_t goal_len, size_t candidate_len)
 297 {
 298   return BASE_COST * MAX (goal_len, candidate_len) / 2;
 299 }
 300
 301 /* Verify that the cutoff for "meaningfulness" of suggestions is at least as
 302    conservative as in older GCC releases.
 303
 304    This should ensure that we don't offer additional meaningless
 305    suggestions (apart from those for which transposition has helped).  */
 306
 307 static void
 308 test_get_edit_distance_cutoff ()
 309 {
 310   for (size_t goal_len = 0; goal_len < 30; goal_len++)
 311     for (size_t candidate_len = 0; candidate_len < 30; candidate_len++)
 312       ASSERT_TRUE (get_edit_distance_cutoff (goal_len, candidate_len)
 313                    <= get_old_cutoff (goal_len, candidate_len));
 314 }
 315
 316 /* Assert that CANDIDATE is offered as a suggestion for TARGET.  */
 317
 318 static void
 319 assert_suggested_for (const location &loc, const char *candidate,
 320                       const char *target)
 321 {
 322   auto_vec<const char *> candidates;
 323   candidates.safe_push (candidate);
 324   ASSERT_EQ_AT (loc, candidate, find_closest_string (target, &candidates));
 325 }
 326
 327 /* Assert that CANDIDATE is offered as a suggestion for TARGET.  */
 328
 329 #define ASSERT_SUGGESTED_FOR(CANDIDATE, TARGET)                 \
 330   SELFTEST_BEGIN_STMT                                                   \
 331     assert_suggested_for (SELFTEST_LOCATION, CANDIDATE, TARGET);        \
 332   SELFTEST_END_STMT
 333
 334 /* Assert that CANDIDATE is not offered as a suggestion for TARGET.  */
 335
 336 static void
 337 assert_not_suggested_for (const location &loc, const char *candidate,
 338                           const char *target)
 339 {
 340   auto_vec<const char *> candidates;
 341   candidates.safe_push (candidate);
 342   ASSERT_EQ_AT (loc, NULL, find_closest_string (target, &candidates));
 343 }
 344
 345 /* Assert that CANDIDATE is not offered as a suggestion for TARGET.  */
 346
 347 #define ASSERT_NOT_SUGGESTED_FOR(CANDIDATE, TARGET)                     \
 348   SELFTEST_BEGIN_STMT                                                   \
 349     assert_not_suggested_for (SELFTEST_LOCATION, CANDIDATE, TARGET);    \
 350   SELFTEST_END_STMT
 351
 352 /* Verify that we offer varous suggestions that are meaningful,
 353    and that we don't offer various other ones that aren't (PR c/82967).  */
 354
 355 static void
 356 test_suggestions ()
 357 {
 358   /* Good suggestions.  */
 359
 360   ASSERT_SUGGESTED_FOR ("m_bar", "bar");
 361   // dist == 2, max_length == 5, min_length == 3
 362
 363   ASSERT_SUGGESTED_FOR ("MACRO", "MACRAME");
 364   // dist == 3, max_length == 7, min_length == 5
 365
 366   ASSERT_SUGGESTED_FOR ("gtk_widget_show_all", "GtkWidgetShowAll");
 367   // dist == 7, max_length == 16, min_length = 19
 368
 369   ASSERT_SUGGESTED_FOR ("ab", "ac");
 370   // dist == 1, max_length == min_length = 2
 371
 372   ASSERT_SUGGESTED_FOR ("ab", "a");
 373   // dist == 1, max_length == 2, min_length = 1
 374
 375   /* Bad suggestions.  */
 376
 377   ASSERT_NOT_SUGGESTED_FOR ("a", "b");
 378   // dist == 1, max_length == min_length = 1
 379
 380   ASSERT_NOT_SUGGESTED_FOR ("sqrt", "assert");
 381   // dist == 3, max_length 6, min_length == 4
 382
 383   ASSERT_NOT_SUGGESTED_FOR ("INT8_MAX", "PATH_MAX");
 384   // dist == 3, max_length == min_length == 8
 385
 386   ASSERT_NOT_SUGGESTED_FOR ("nice", "time");
 387   ASSERT_NOT_SUGGESTED_FOR ("nanl", "name");
 388   // dist == 2, max_length == min_length == 4
 389
 390   ASSERT_NOT_SUGGESTED_FOR ("carg", "bar");
 391   ASSERT_NOT_SUGGESTED_FOR ("char", "bar");
 392   // dist == 2, max_length == 4, min_length == 3
 393
 394   ASSERT_NOT_SUGGESTED_FOR ("-optimize", "fsanitize");
 395   // dist == 5, max_length == min_length == 9
 396
 397   ASSERT_NOT_SUGGESTED_FOR ("__DATE__", "__i386__");
 398   // dist == 4, max_length == min_length == 8
 399
 400   ASSERT_NOT_SUGGESTED_FOR ("start_input_device", "InputDevice");
 401   // dist == 9, max_length == 18, min_length == 11
 402 }
 403
 404 /* Verify that find_closest_string is sane.  */
 405
 406 static void
 407 test_find_closest_string ()
 408 {
 409   auto_vec<const char *> candidates;
 410
 411   /* Verify that it can handle an empty vec.  */
 412   ASSERT_EQ (NULL, find_closest_string ("", &candidates));
 413
 414   /* Verify that it works sanely for non-empty vecs.  */
 415   candidates.safe_push ("apple");
 416   candidates.safe_push ("banana");
 417   candidates.safe_push ("cherry");
 418
 419   ASSERT_STREQ ("apple", find_closest_string ("app", &candidates));
 420   ASSERT_STREQ ("banana", find_closest_string ("banyan", &candidates));
 421   ASSERT_STREQ ("cherry", find_closest_string ("berry", &candidates));
 422   ASSERT_EQ (NULL, find_closest_string ("not like the others", &candidates));
 423
 424   /* The order of the vec can matter, but it should not matter for these
 425      inputs.  */
 426   candidates.truncate (0);
 427   candidates.safe_push ("cherry");
 428   candidates.safe_push ("banana");
 429   candidates.safe_push ("apple");
 430   ASSERT_STREQ ("apple", find_closest_string ("app", &candidates));
 431   ASSERT_STREQ ("banana", find_closest_string ("banyan", &candidates));
 432   ASSERT_STREQ ("cherry", find_closest_string ("berry", &candidates));
 433   ASSERT_EQ (NULL, find_closest_string ("not like the others", &candidates));
 434
 435   /* If the goal string somehow makes it into the candidate list, offering
 436      it as a suggestion will be nonsensical.  Verify that we don't offer such
 437      suggestions.  */
 438   ASSERT_EQ (NULL, find_closest_string ("banana", &candidates));
 439
 440   /* Example from PR 69968 where transposition helps.  */
 441   candidates.truncate (0);
 442   candidates.safe_push("coordx");
 443   candidates.safe_push("coordy");
 444   candidates.safe_push("coordz");
 445   candidates.safe_push("coordx1");
 446   candidates.safe_push("coordy1");
 447   candidates.safe_push("coordz1");
 448   ASSERT_STREQ ("coordz1", find_closest_string ("coorzd1", &candidates));
 449
 450   candidates.truncate (0);
 451   candidates.safe_push ("DWARF_GNAT_ENCODINGS_GDB");
 452   candidates.safe_push ("DWARF_GNAT_ENCODINGS_ALL");
 453   candidates.safe_push ("DWARF_GNAT_ENCODINGS_MINIMAL");
 454   ASSERT_STREQ ("DWARF_GNAT_ENCODINGS_ALL",
 455                 find_closest_string ("DWARF_GNAT_ENCODINGS_all",
 456                                      &candidates));
 457
 458   /* The same as the previous test, but with a different order of
 459      candidates.  */
 460   candidates.truncate (0);
 461   candidates.safe_push ("DWARF_GNAT_ENCODINGS_ALL");
 462   candidates.safe_push ("DWARF_GNAT_ENCODINGS_GDB");
 463   candidates.safe_push ("DWARF_GNAT_ENCODINGS_MINIMAL");
 464   ASSERT_STREQ ("DWARF_GNAT_ENCODINGS_ALL",
 465                 find_closest_string ("DWARF_GNAT_ENCODINGS_all",
 466                                      &candidates));
 467 }
 468
 469 /* Test data for test_metric_conditions.  */
 470
 471 static const char * const test_data[] = {
 472   "",
 473   "foo",
 474   "food",
 475   "boo",
 476   "1234567890123456789012345678901234567890123456789012345678901234567890",
 477   "abc",
 478   "ac",
 479   "ca",
 480 };
 481
 482 /* Verify that get_edit_distance appears to be a sane distance function,
 483    even though it doesn't satisfy the conditions for being a metric.  (This
 484    is because the triangle inequality fails to hold: the distance between
 485    "ca" and "ac" is 1, and so is the distance between "abc" and "ac", but
 486    the distance between "abc" and "ca" is 3. Algorithms that calculate the
 487    true Levenshtein-Damerau metric are much more expensive.)  */
 488
 489 static void
 490 test_metric_conditions ()
 491 {
 492   const int num_test_cases = sizeof (test_data) / sizeof (test_data[0]);
 493
 494   for (int i = 0; i < num_test_cases; i++)
 495     {
 496       for (int j = 0; j < num_test_cases; j++)
 497         {
 498           edit_distance_t dist_ij
 499             = get_edit_distance (test_data[i], test_data[j]);
 500
 501           /* Identity of indiscernibles: d(i, j) > 0 iff i == j.  */
 502           if (i == j)
 503             ASSERT_EQ (dist_ij, 0);
 504           else
 505             ASSERT_TRUE (dist_ij > 0);
 506
 507           /* Symmetry: d(i, j) == d(j, i).  */
 508           edit_distance_t dist_ji
 509             = get_edit_distance (test_data[j], test_data[i]);
 510           ASSERT_EQ (dist_ij, dist_ji);
 511         }
 512     }
 513 }
 514
 515 /* Run all of the selftests within this file.  */
 516
 517 void
 518 spellcheck_c_tests ()
 519 {
 520   test_edit_distances ();
 521   test_get_edit_distance_cutoff ();
 522   test_suggestions ();
 523   test_find_closest_string ();
 524   test_metric_conditions ();
 525 }
 526
 527 } // namespace selftest
 528
 529 #endif /* #if CHECKING_P */