1 /* Find near-matches for strings and identifiers.
2 Copyright (C) 2015-2016 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
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
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
;
27 extern edit_distance_t
28 levenshtein_distance (const char *s
, int len_s
,
29 const char *t
, int len_t
);
31 extern edit_distance_t
32 levenshtein_distance (const char *s
, const char *t
);
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
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
48 template <typename TYPE
>
49 struct edit_distance_traits
{};
51 /* Specialization of edit_distance_traits for C-style strings. */
54 struct edit_distance_traits
<const char *>
56 static size_t get_length (const char *str
)
62 static const char *get_string (const char *str
)
69 /* A type for use when determining the best match against a string,
70 expressed as a template so that we can match against various
71 string-like types (const char *, frontend identifiers, and preprocessor
74 This type accumulates the best possible match against GOAL_TYPE for
75 a sequence of elements of CANDIDATE_TYPE, whilst minimizing the
76 number of calls to levenshtein_distance and to
77 edit_distance_traits<T>::get_length. */
79 template <typename GOAL_TYPE
, typename CANDIDATE_TYPE
>
83 typedef GOAL_TYPE goal_t
;
84 typedef CANDIDATE_TYPE candidate_t
;
85 typedef edit_distance_traits
<goal_t
> goal_traits
;
86 typedef edit_distance_traits
<candidate_t
> candidate_traits
;
90 best_match (GOAL_TYPE goal
,
91 edit_distance_t best_distance_so_far
= MAX_EDIT_DISTANCE
)
92 : m_goal (goal_traits::get_string (goal
)),
93 m_goal_len (goal_traits::get_length (goal
)),
94 m_best_candidate (NULL
),
95 m_best_distance (best_distance_so_far
)
98 /* Compare the edit distance between CANDIDATE and m_goal,
99 and if it's the best so far, record it. */
101 void consider (candidate_t candidate
)
103 size_t candidate_len
= candidate_traits::get_length (candidate
);
105 /* Calculate a lower bound on the candidate's distance to the goal,
106 based on the difference in lengths; it will require at least
107 this many insertions/deletions. */
108 edit_distance_t min_candidate_distance
109 = abs ((ssize_t
)candidate_len
- (ssize_t
)m_goal_len
);
111 /* If the candidate's length is sufficiently different to that
112 of the goal string, then the number of insertions/deletions
113 may be >= the best distance so far. If so, we can reject
114 the candidate immediately without needing to compute
115 the exact distance, since it won't be an improvement. */
116 if (min_candidate_distance
>= m_best_distance
)
119 /* If the candidate will be unable to beat the criterion in
120 get_best_meaningful_candidate, reject it without computing
121 the exact distance. */
122 unsigned int cutoff
= MAX (m_goal_len
, candidate_len
) / 2;
123 if (min_candidate_distance
> cutoff
)
126 /* Otherwise, compute the distance and see if the candidate
127 has beaten the previous best value. */
129 = levenshtein_distance (m_goal
, m_goal_len
,
130 candidate_traits::get_string (candidate
),
132 if (dist
< m_best_distance
)
134 m_best_distance
= dist
;
135 m_best_candidate
= candidate
;
136 m_best_candidate_len
= candidate_len
;
140 /* Assuming that BEST_CANDIDATE is known to be better than
141 m_best_candidate, update (without recomputing the edit distance to
144 void set_best_so_far (CANDIDATE_TYPE best_candidate
,
145 edit_distance_t best_distance
,
146 size_t best_candidate_len
)
148 gcc_assert (best_distance
< m_best_distance
);
149 m_best_candidate
= best_candidate
;
150 m_best_distance
= best_distance
;
151 m_best_candidate_len
= best_candidate_len
;
154 /* Get the best candidate so far, but applying a filter to ensure
155 that we return NULL if none of the candidates are close to the goal,
156 to avoid offering nonsensical suggestions to the user. */
158 candidate_t
get_best_meaningful_candidate () const
160 /* If more than half of the letters were misspelled, the suggestion is
161 likely to be meaningless. */
162 if (m_best_candidate
)
164 unsigned int cutoff
= MAX (m_goal_len
, m_best_candidate_len
) / 2;
165 if (m_best_distance
> cutoff
)
169 /* If the goal string somehow makes it into the candidate list, offering
170 it as a suggestion will be nonsensical e.g.
171 'constexpr' does not name a type; did you mean 'constexpr'?
172 Ultimately such suggestions are due to bugs in constructing the
173 candidate list, but as a band-aid, do not offer suggestions for
174 distance == 0 (where candidate == goal). */
175 if (m_best_distance
== 0)
178 return m_best_candidate
;
181 edit_distance_t
get_best_distance () const { return m_best_distance
; }
182 size_t get_best_candidate_length () const { return m_best_candidate_len
; }
187 candidate_t m_best_candidate
;
188 edit_distance_t m_best_distance
;
189 size_t m_best_candidate_len
;
192 #endif /* GCC_SPELLCHECK_H */