clang-tools  10.0.0svn
FuzzyMatch.h
Go to the documentation of this file.
1 //===--- FuzzyMatch.h - Approximate identifier matching ---------*- C++-*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements fuzzy-matching of strings against identifiers.
10 // It indicates both the existence and quality of a match:
11 // 'eb' matches both 'emplace_back' and 'embed', the former has a better score.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_FUZZYMATCH_H
16 #define LLVM_CLANG_TOOLS_EXTRA_CLANGD_FUZZYMATCH_H
17 
18 #include "llvm/ADT/ArrayRef.h"
19 #include "llvm/ADT/Optional.h"
20 #include "llvm/ADT/SmallString.h"
21 #include "llvm/ADT/StringRef.h"
22 #include "llvm/Support/raw_ostream.h"
23 
24 namespace clang {
25 namespace clangd {
26 
27 // Utilities for word segmentation.
28 // FuzzyMatcher already incorporates this logic, so most users don't need this.
29 //
30 // A name like "fooBar_baz" consists of several parts foo, bar, baz.
31 // Aligning segmentation of word and pattern improves the fuzzy-match.
32 // For example: [lol] matches "LaughingOutLoud" better than "LionPopulation"
33 //
34 // First we classify each character into types (uppercase, lowercase, etc).
35 // Then we look at the sequence: e.g. [upper, lower] is the start of a segment.
36 
37 // We distinguish the types of characters that affect segmentation.
38 // It's not obvious how to segment digits, we treat them as lowercase letters.
39 // As we don't decode UTF-8, we treat bytes over 127 as lowercase too.
40 // This means we require exact (case-sensitive) match for those characters.
41 enum CharType : unsigned char {
42  Empty = 0, // Before-the-start and after-the-end (and control chars).
43  Lower = 1, // Lowercase letters, digits, and non-ASCII bytes.
44  Upper = 2, // Uppercase letters.
45  Punctuation = 3, // ASCII punctuation (including Space)
46 };
47 // A CharTypeSet is a bitfield representing all the character types in a word.
48 // Its bits are 1<<Empty, 1<<Lower, etc.
49 using CharTypeSet = unsigned char;
50 
51 // Each character's Role is the Head or Tail of a segment, or a Separator.
52 // e.g. XMLHttpRequest_Async
53 // +--+---+------ +----
54 // ^Head ^Tail ^Separator
55 enum CharRole : unsigned char {
56  Unknown = 0, // Stray control characters or impossible states.
57  Tail = 1, // Part of a word segment, but not the first character.
58  Head = 2, // The first character of a word segment.
59  Separator = 3, // Punctuation characters that separate word segments.
60 };
61 
62 // Compute segmentation of Text.
63 // Character roles are stored in Roles (Roles.size() must equal Text.size()).
64 // The set of character types encountered is returned, this may inform
65 // heuristics for dealing with poorly-segmented identifiers like "strndup".
66 CharTypeSet calculateRoles(llvm::StringRef Text,
67  llvm::MutableArrayRef<CharRole> Roles);
68 
69 // A matcher capable of matching and scoring strings against a single pattern.
70 // It's optimized for matching against many strings - match() does not allocate.
71 class FuzzyMatcher {
72 public:
73  // Characters beyond MaxPat are ignored.
74  FuzzyMatcher(llvm::StringRef Pattern);
75 
76  // If Word matches the pattern, return a score indicating the quality match.
77  // Scores usually fall in a [0,1] range, with 1 being a very good score.
78  // "Super" scores in (1,2] are possible if the pattern is the full word.
79  // Characters beyond MaxWord are ignored.
80  llvm::Optional<float> match(llvm::StringRef Word);
81 
82  llvm::StringRef pattern() const { return llvm::StringRef(Pat, PatN); }
83  bool empty() const { return PatN == 0; }
84 
85  // Dump internal state from the last match() to the stream, for debugging.
86  // Returns the pattern with [] around matched characters, e.g.
87  // [u_p] + "unique_ptr" --> "[u]nique[_p]tr"
88  llvm::SmallString<256> dumpLast(llvm::raw_ostream &) const;
89 
90 private:
91  // We truncate the pattern and the word to bound the cost of matching.
92  constexpr static int MaxPat = 63, MaxWord = 127;
93  // Action describes how a word character was matched to the pattern.
94  // It should be an enum, but this causes bitfield problems:
95  // - for MSVC the enum type must be explicitly unsigned for correctness
96  // - GCC 4.8 complains not all values fit if the type is unsigned
97  using Action = bool;
98  constexpr static Action Miss = false; // Word character was skipped.
99  constexpr static Action Match = true; // Matched against a pattern character.
100 
101  bool init(llvm::StringRef Word);
102  void buildGraph();
103  bool allowMatch(int P, int W, Action Last) const;
104  int skipPenalty(int W, Action Last) const;
105  int matchBonus(int P, int W, Action Last) const;
106 
107  // Pattern data is initialized by the constructor, then constant.
108  char Pat[MaxPat]; // Pattern data
109  int PatN; // Length
110  char LowPat[MaxPat]; // Pattern in lowercase
111  CharRole PatRole[MaxPat]; // Pattern segmentation info
112  CharTypeSet PatTypeSet; // Bitmask of 1<<CharType for all Pattern characters
113  float ScoreScale; // Normalizes scores for the pattern length.
114 
115  // Word data is initialized on each call to match(), mostly by init().
116  char Word[MaxWord]; // Word data
117  int WordN; // Length
118  char LowWord[MaxWord]; // Word in lowercase
119  CharRole WordRole[MaxWord]; // Word segmentation info
120  CharTypeSet WordTypeSet; // Bitmask of 1<<CharType for all Word characters
121  bool WordContainsPattern; // Simple substring check
122 
123  // Cumulative best-match score table.
124  // Boundary conditions are filled in by the constructor.
125  // The rest is repopulated for each match(), by buildGraph().
126  struct ScoreInfo {
127  signed int Score : 15;
128  Action Prev : 1;
129  };
130  ScoreInfo Scores[MaxPat + 1][MaxWord + 1][/* Last Action */ 2];
131 };
132 
133 } // namespace clangd
134 } // namespace clang
135 
136 #endif
llvm::Optional< float > Score
unsigned char CharTypeSet
Definition: FuzzyMatch.h:49
llvm::Optional< float > match(llvm::StringRef Word)
Definition: FuzzyMatch.cpp:92
CharTypeSet calculateRoles(llvm::StringRef Text, llvm::MutableArrayRef< CharRole > Roles)
Definition: FuzzyMatch.cpp:154
FuzzyMatcher(llvm::StringRef Pattern)
Definition: FuzzyMatch.cpp:76
llvm::SmallString< 256 > dumpLast(llvm::raw_ostream &) const
Definition: FuzzyMatch.cpp:308
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//
llvm::StringRef pattern() const
Definition: FuzzyMatch.h:82