1 //===--- Trigram.cpp - 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 #include "Trigram.h"
10 #include "FuzzyMatch.h"
11 #include "Token.h"
12 #include "llvm/ADT/ArrayRef.h"
13 #include "llvm/ADT/DenseSet.h"
14 #include "llvm/ADT/STLExtras.h"
15 #include "llvm/ADT/StringExtras.h"
16 #include <cctype>
17 #include <queue>
18 #include <string>
19
20 namespace clang {
21 namespace clangd {
22 namespace dex {
23
24 // Produce trigrams (including duplicates) and pass them to Out().
25 template <typename Func>
identifierTrigrams(llvm::StringRef Identifier,Func Out)26 static void identifierTrigrams(llvm::StringRef Identifier, Func Out) {
27 // Apply fuzzy matching text segmentation.
28 std::vector<CharRole> Roles(Identifier.size());
29 calculateRoles(Identifier,
30 llvm::makeMutableArrayRef(Roles.data(), Identifier.size()));
31
32 std::string LowercaseIdentifier = Identifier.lower();
33
34 // For each character, store indices of the characters to which fuzzy matching
35 // algorithm can jump. There are 3 possible variants:
36 //
37 // * Next Tail - next character from the same segment
38 // * Next Head - front character of the next segment
39 //
40 // Next stores tuples of three indices in the presented order, if a variant is
41 // not available then 0 is stored.
42 std::vector<std::array<unsigned, 3>> Next(LowercaseIdentifier.size());
43 unsigned NextTail = 0, NextHead = 0;
44 for (int I = LowercaseIdentifier.size() - 1; I >= 0; --I) {
45 Next[I] = {{NextTail, NextHead}};
46 NextTail = Roles[I] == Tail ? I : 0;
47 if (Roles[I] == Head) {
48 NextHead = I;
49 }
50 }
51
52 // Iterate through valid sequences of three characters Fuzzy Matcher can
53 // process.
54 for (size_t I = 0; I < LowercaseIdentifier.size(); ++I) {
55 // Skip delimiters.
56 if (Roles[I] != Head && Roles[I] != Tail)
57 continue;
58 for (const unsigned J : Next[I]) {
59 if (J == 0)
60 continue;
61 for (const unsigned K : Next[J]) {
62 if (K == 0)
63 continue;
64 Out(Trigram(LowercaseIdentifier[I], LowercaseIdentifier[J],
65 LowercaseIdentifier[K]));
66 }
67 }
68 }
69 // Emit short-query trigrams: FooBar -> f, fo, fb.
70 if (!LowercaseIdentifier.empty())
71 Out(Trigram(LowercaseIdentifier[0]));
72 if (LowercaseIdentifier.size() >= 2)
73 Out(Trigram(LowercaseIdentifier[0], LowercaseIdentifier[1]));
74 for (size_t I = 1; I < LowercaseIdentifier.size(); ++I)
75 if (Roles[I] == Head) {
76 Out(Trigram(LowercaseIdentifier[0], LowercaseIdentifier[I]));
77 break;
78 }
79 }
80
generateIdentifierTrigrams(llvm::StringRef Identifier,std::vector<Trigram> & Result)81 void generateIdentifierTrigrams(llvm::StringRef Identifier,
82 std::vector<Trigram> &Result) {
83 // Empirically, scanning for duplicates is faster with fewer trigrams, and
84 // a hashtable is faster with more. This is a hot path, so dispatch based on
85 // expected number of trigrams. Longer identifiers produce more trigrams.
86 // The magic number was tuned by running IndexBenchmark.DexBuild.
87 constexpr unsigned ManyTrigramsIdentifierThreshold = 14;
88 Result.clear();
89 if (Identifier.size() < ManyTrigramsIdentifierThreshold) {
90 identifierTrigrams(Identifier, [&](Trigram T) {
91 if (!llvm::is_contained(Result, T))
92 Result.push_back(T);
93 });
94 } else {
95 identifierTrigrams(Identifier, [&](Trigram T) { Result.push_back(T); });
96 llvm::sort(Result);
97 Result.erase(std::unique(Result.begin(), Result.end()), Result.end());
98 }
99 }
100
generateQueryTrigrams(llvm::StringRef Query)101 std::vector<Token> generateQueryTrigrams(llvm::StringRef Query) {
102 if (Query.empty())
103 return {};
104 std::string LowercaseQuery = Query.lower();
105 if (Query.size() < 3) // short-query trigrams only
106 return {Token(Token::Kind::Trigram, LowercaseQuery)};
107
108 // Apply fuzzy matching text segmentation.
109 std::vector<CharRole> Roles(Query.size());
110 calculateRoles(Query, llvm::makeMutableArrayRef(Roles.data(), Query.size()));
111
112 llvm::DenseSet<Token> UniqueTrigrams;
113 std::string Chars;
114 for (unsigned I = 0; I < Query.size(); ++I) {
115 if (Roles[I] != Head && Roles[I] != Tail)
116 continue; // Skip delimiters.
117 Chars.push_back(LowercaseQuery[I]);
118 if (Chars.size() > 3)
119 Chars.erase(Chars.begin());
120 if (Chars.size() == 3)
121 UniqueTrigrams.insert(Token(Token::Kind::Trigram, Chars));
122 }
123
124 return {UniqueTrigrams.begin(), UniqueTrigrams.end()};
125 }
126
127 } // namespace dex
128 } // namespace clangd
129 } // namespace clang
130