1//===--- Trigram.h - Trigram generation for Fuzzy 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/// \file
10/// Trigrams are attributes of the symbol unqualified name used to effectively
11/// extract symbols which can be fuzzy-matched given user query from the
12/// inverted index. To match query with the extracted set of trigrams Q, the set
13/// of generated trigrams T for identifier (unqualified symbol name) should
14/// contain all items of Q, i.e. Q ⊆ T.
15///
16/// Trigram sets extracted from unqualified name and from query are different:
17/// the set of query trigrams only contains consecutive sequences of three
18/// characters (which is only a subset of all trigrams generated for an
19/// identifier).
20///
21//===----------------------------------------------------------------------===//
22
23#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_INDEX_DEX_TRIGRAM_H
24#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_INDEX_DEX_TRIGRAM_H
25
26#include "index/dex/Token.h"
27#include "llvm/ADT/bit.h"
28
29#include <array>
30#include <string>
31
32namespace clang {
33namespace clangd {
34namespace dex {
35
36// Compact representation of a trigram (string with up to 3 characters).
37// Trigram generation is the hot path of indexing, so Token is too wasteful.
38class Trigram {
39 std::array<char, 4> Data; // Last element is length.
40 // Steal some invalid bit patterns for DenseMap sentinels.
41 enum class Sentinel { Tombstone = 4, Empty = 5 };
42 Trigram(Sentinel S) : Data{0, 0, 0, static_cast<char>(S)} {}
43 uint32_t id() const { return llvm::bit_cast<uint32_t>(from: Data); }
44
45public:
46 Trigram() : Data{0, 0, 0, 0} {}
47 Trigram(char A) : Data{A, 0, 0, 1} {}
48 Trigram(char A, char B) : Data{A, B, 0, 2} {}
49 Trigram(char A, char B, char C) : Data{A, B, C, 3} {}
50 std::string str() const { return std::string(Data.data(), Data[3]); }
51 friend struct ::llvm::DenseMapInfo<Trigram>;
52 friend bool operator==(Trigram L, Trigram R) { return L.id() == R.id(); }
53 friend bool operator<(Trigram L, Trigram R) { return L.id() < R.id(); }
54};
55
56/// Produces list of unique fuzzy-search trigrams from unqualified symbol.
57/// The trigrams give the 3-character query substrings this symbol can match.
58///
59/// The symbol's name is broken into segments, e.g. "FooBar" has two segments.
60/// Trigrams can start at any character in the input. Then we can choose to move
61/// to the next character or to the start of the next segment.
62///
63/// Short trigrams (length 1-2) are used for short queries. These are:
64/// - prefixes of the identifier, of length 1 and 2
65/// - the first character + next head character
66///
67/// For "FooBar" we get the following trigrams:
68/// {f, fo, fb, foo, fob, fba, oob, oba, bar}.
69///
70/// Trigrams are lowercase, as trigram matching is case-insensitive.
71/// Trigrams in the list are deduplicated.
72void generateIdentifierTrigrams(llvm::StringRef Identifier,
73 std::vector<Trigram> &Out);
74
75/// Returns list of unique fuzzy-search trigrams given a query.
76///
77/// Query is segmented using FuzzyMatch API and downcasted to lowercase. Then,
78/// the simplest trigrams - sequences of three consecutive letters and digits
79/// are extracted and returned after deduplication.
80///
81/// For short queries (less than 3 characters with Head or Tail roles in Fuzzy
82/// Matching segmentation) this returns a single trigram with the first
83/// characters (up to 3) to perform prefix match.
84std::vector<Token> generateQueryTrigrams(llvm::StringRef Query);
85
86} // namespace dex
87} // namespace clangd
88} // namespace clang
89
90namespace llvm {
91template <> struct DenseMapInfo<clang::clangd::dex::Trigram> {
92 using Trigram = clang::clangd::dex::Trigram;
93 static inline Trigram getEmptyKey() {
94 return Trigram(Trigram::Sentinel::Empty);
95 }
96 static inline Trigram getTombstoneKey() {
97 return Trigram(Trigram::Sentinel::Tombstone);
98 }
99 static unsigned getHashValue(Trigram V) {
100 // Finalize step from MurmurHash3.
101 uint32_t X = V.id();
102 X ^= X >> 16;
103 X *= uint32_t{0x85ebca6b};
104 X ^= X >> 13;
105 X *= uint32_t{0xc2b2ae35};
106 X ^= X >> 16;
107 return X;
108 }
109 static bool isEqual(const Trigram &LHS, const Trigram &RHS) {
110 return LHS == RHS;
111 }
112};
113} // namespace llvm
114
115#endif // LLVM_CLANG_TOOLS_EXTRA_CLANGD_INDEX_DEX_TRIGRAM_H
116

source code of clang-tools-extra/clangd/index/dex/Trigram.h