2018-11-09 Richard Biener <rguenther@suse.de>
[official-gcc.git] / gcc / spellcheck.h
blobe8fa77ceaa810d91580aae903edf90ca6debaa71
1 /* Find near-matches for strings and identifiers.
2 Copyright (C) 2015-2018 Free Software Foundation, Inc.
4 This file is part of GCC.
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.
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.
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/>. */
20 #ifndef GCC_SPELLCHECK_H
21 #define GCC_SPELLCHECK_H
23 typedef unsigned int edit_distance_t;
24 const edit_distance_t MAX_EDIT_DISTANCE = UINT_MAX;
26 /* spellcheck.c */
27 extern edit_distance_t
28 get_edit_distance (const char *s, int len_s,
29 const char *t, int len_t);
31 extern edit_distance_t
32 get_edit_distance (const char *s, const char *t);
34 extern const char *
35 find_closest_string (const char *target,
36 const auto_vec<const char *> *candidates);
38 /* A traits class for describing a string-like type usable by
39 class best_match.
40 Specializations should provide the implementations of the following:
42 static size_t get_length (TYPE);
43 static const char *get_string (TYPE);
45 get_string should return a non-NULL ptr, which does not need to be
46 0-terminated. */
48 template <typename TYPE>
49 struct edit_distance_traits {};
51 /* Specialization of edit_distance_traits for C-style strings. */
53 template <>
54 struct edit_distance_traits<const char *>
56 static size_t get_length (const char *str)
58 gcc_assert (str);
59 return strlen (str);
62 static const char *get_string (const char *str)
64 gcc_assert (str);
65 return str;
69 extern edit_distance_t get_edit_distance_cutoff (size_t goal_len,
70 size_t candidate_len);
72 /* A type for use when determining the best match against a string,
73 expressed as a template so that we can match against various
74 string-like types (const char *, frontend identifiers, and preprocessor
75 macros).
77 This type accumulates the best possible match against GOAL_TYPE for
78 a sequence of elements of CANDIDATE_TYPE, whilst minimizing the
79 number of calls to get_edit_distance and to
80 edit_distance_traits<T>::get_length. */
82 template <typename GOAL_TYPE, typename CANDIDATE_TYPE>
83 class best_match
85 public:
86 typedef GOAL_TYPE goal_t;
87 typedef CANDIDATE_TYPE candidate_t;
88 typedef edit_distance_traits<goal_t> goal_traits;
89 typedef edit_distance_traits<candidate_t> candidate_traits;
91 /* Constructor. */
93 best_match (GOAL_TYPE goal,
94 edit_distance_t best_distance_so_far = MAX_EDIT_DISTANCE)
95 : m_goal (goal_traits::get_string (goal)),
96 m_goal_len (goal_traits::get_length (goal)),
97 m_best_candidate (NULL),
98 m_best_distance (best_distance_so_far)
101 /* Compare the edit distance between CANDIDATE and m_goal,
102 and if it's the best so far, record it. */
104 void consider (candidate_t candidate)
106 size_t candidate_len = candidate_traits::get_length (candidate);
108 /* Calculate a lower bound on the candidate's distance to the goal,
109 based on the difference in lengths; it will require at least
110 this many insertions/deletions. */
111 edit_distance_t min_candidate_distance
112 = abs ((ssize_t)candidate_len - (ssize_t)m_goal_len);
114 /* If the candidate's length is sufficiently different to that
115 of the goal string, then the number of insertions/deletions
116 may be >= the best distance so far. If so, we can reject
117 the candidate immediately without needing to compute
118 the exact distance, since it won't be an improvement. */
119 if (min_candidate_distance >= m_best_distance)
120 return;
122 /* If the candidate will be unable to beat the criterion in
123 get_best_meaningful_candidate, reject it without computing
124 the exact distance. */
125 edit_distance_t cutoff = get_cutoff (candidate_len);
126 if (min_candidate_distance > cutoff)
127 return;
129 /* Otherwise, compute the distance and see if the candidate
130 has beaten the previous best value. */
131 edit_distance_t dist
132 = get_edit_distance (m_goal, m_goal_len,
133 candidate_traits::get_string (candidate),
134 candidate_len);
135 if (dist < m_best_distance)
137 m_best_distance = dist;
138 m_best_candidate = candidate;
139 m_best_candidate_len = candidate_len;
143 /* Assuming that BEST_CANDIDATE is known to be better than
144 m_best_candidate, update (without recomputing the edit distance to
145 the goal). */
147 void set_best_so_far (CANDIDATE_TYPE best_candidate,
148 edit_distance_t best_distance,
149 size_t best_candidate_len)
151 gcc_assert (best_distance < m_best_distance);
152 m_best_candidate = best_candidate;
153 m_best_distance = best_distance;
154 m_best_candidate_len = best_candidate_len;
157 /* Generate the maximum edit distance for which we consider a suggestion
158 to be meaningful, given a candidate of length CANDIDATE_LEN. */
160 edit_distance_t get_cutoff (size_t candidate_len) const
162 return ::get_edit_distance_cutoff (m_goal_len, candidate_len);
165 /* Get the best candidate so far, but applying a filter to ensure
166 that we return NULL if none of the candidates are close to the goal,
167 to avoid offering nonsensical suggestions to the user. */
169 candidate_t get_best_meaningful_candidate () const
171 /* If the edit distance is too high, the suggestion is likely to be
172 meaningless. */
173 if (m_best_candidate)
175 edit_distance_t cutoff = get_cutoff (m_best_candidate_len);
176 if (m_best_distance > cutoff)
177 return NULL;
180 /* If the goal string somehow makes it into the candidate list, offering
181 it as a suggestion will be nonsensical e.g.
182 'constexpr' does not name a type; did you mean 'constexpr'?
183 Ultimately such suggestions are due to bugs in constructing the
184 candidate list, but as a band-aid, do not offer suggestions for
185 distance == 0 (where candidate == goal). */
186 if (m_best_distance == 0)
187 return NULL;
189 return m_best_candidate;
192 /* Get the closest candidate so far, without applying any filtering. */
194 candidate_t blithely_get_best_candidate () const
196 return m_best_candidate;
199 edit_distance_t get_best_distance () const { return m_best_distance; }
200 size_t get_best_candidate_length () const { return m_best_candidate_len; }
202 private:
203 const char *m_goal;
204 size_t m_goal_len;
205 candidate_t m_best_candidate;
206 edit_distance_t m_best_distance;
207 size_t m_best_candidate_len;
210 #endif /* GCC_SPELLCHECK_H */