1 //===--- Iterator.h - Query Symbol Retrieval --------------------*- 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 /// Symbol index queries consist of specific requirements for the requested
11 /// symbol, such as high fuzzy matching score, scope, type etc. The lists of all
12 /// symbols matching some criteria (e.g. belonging to "clang::clangd::" scope)
13 /// are expressed in a form of Search Tokens which are stored in the inverted
14 /// index. Inverted index maps these tokens to the posting lists - sorted (by
15 /// symbol quality) sequences of symbol IDs matching the token, e.g. scope token
16 /// "clangd::clangd::" is mapped to the list of IDs of all symbols which are
17 /// declared in this namespace. Search queries are build from a set of
18 /// requirements which can be combined with each other forming the query trees.
19 /// The leafs of such trees are posting lists, and the nodes are operations on
20 /// these posting lists, e.g. intersection or union. Efficient processing of
21 /// these multi-level queries is handled by Iterators. Iterators advance through
22 /// all leaf posting lists producing the result of search query, which preserves
23 /// the sorted order of IDs. Having the resulting IDs sorted is important,
24 /// because it allows receiving a certain number of the most valuable items
25 /// (e.g. symbols with highest quality which was the sorting key in the first
26 /// place) without processing all items with requested properties (this might
27 /// not be computationally effective if search request is not very restrictive).
28 //
29 //===----------------------------------------------------------------------===//
30
31 #ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_INDEX_DEX_ITERATOR_H
32 #define LLVM_CLANG_TOOLS_EXTRA_CLANGD_INDEX_DEX_ITERATOR_H
33
34 #include "llvm/Support/raw_ostream.h"
35 #include <algorithm>
36 #include <memory>
37 #include <vector>
38
39 namespace clang {
40 namespace clangd {
41 namespace dex {
42
43 /// Symbol position in the list of all index symbols sorted by a pre-computed
44 /// symbol quality.
45 using DocID = uint32_t;
46
47 /// Iterator is the interface for Query Tree node. The simplest type of Iterator
48 /// is DocumentIterator which is simply a wrapper around PostingList iterator
49 /// and serves as the Query Tree leaf. More sophisticated examples of iterators
50 /// can manage intersection, union of the elements produced by other iterators
51 /// (their children) to form a multi-level Query Tree. The interface is designed
52 /// to be extensible in order to support multiple types of iterators.
53 class Iterator {
54 public:
55 /// Returns true if all valid DocIDs were processed and hence the iterator is
56 /// exhausted.
57 virtual bool reachedEnd() const = 0;
58 /// Moves to next valid DocID. If it doesn't exist, the iterator is exhausted
59 /// and proceeds to the END.
60 ///
61 /// Note: reachedEnd() must be false.
62 virtual void advance() = 0;
63 /// Moves to the first valid DocID which is equal or higher than given ID. If
64 /// it doesn't exist, the iterator is exhausted and proceeds to the END.
65 ///
66 /// Note: reachedEnd() must be false.
67 virtual void advanceTo(DocID ID) = 0;
68 /// Returns the current element this iterator points to.
69 ///
70 /// Note: reachedEnd() must be false.
71 virtual DocID peek() const = 0;
72 /// Informs the iterator that the current document was consumed, and returns
73 /// its boost.
74 ///
75 /// Note: If this iterator has any child iterators that contain the document,
76 /// consume() should be called on those and their boosts incorporated.
77 /// consume() must *not* be called on children that don't contain the current
78 /// doc.
79 virtual float consume() = 0;
80 /// Returns an estimate of advance() calls before the iterator is exhausted.
81 virtual size_t estimateSize() const = 0;
82
~Iterator()83 virtual ~Iterator() {}
84
85 /// Prints a convenient human-readable iterator representation by recursively
86 /// dumping iterators in the following format:
87 ///
88 /// (Type Child1 Child2 ...)
89 ///
90 /// Where Type is the iterator type representation: "&" for And, "|" for Or,
91 /// ChildN is N-th iterator child. Raw iterators over PostingList are
92 /// represented as "[... CurID ...]" where CurID is the current PostingList
93 /// entry being inspected.
94 friend llvm::raw_ostream &operator<<(llvm::raw_ostream &OS,
95 const Iterator &Iterator) {
96 return Iterator.dump(OS);
97 }
98
99 /// Inspect iterator type, used internally for optimizing query trees.
100 enum class Kind { And, Or, True, False, Other };
kind()101 Kind kind() const { return MyKind; }
102
103 protected:
MyKind(MyKind)104 Iterator(Kind MyKind = Kind::Other) : MyKind(MyKind) {}
105
106 private:
107 virtual llvm::raw_ostream &dump(llvm::raw_ostream &OS) const = 0;
108 Kind MyKind;
109 };
110
111 /// Advances the iterator until it is exhausted. Returns pairs of document IDs
112 /// with the corresponding boosting score.
113 ///
114 /// Boosting can be seen as a compromise between retrieving too many items and
115 /// calculating finals score for each of them (which might be very expensive)
116 /// and not retrieving enough items so that items with very high final score
117 /// would not be processed. Boosting score is a computationally efficient way
118 /// to acquire preliminary scores of requested items.
119 std::vector<std::pair<DocID, float>> consume(Iterator &It);
120
121 namespace detail {
122 // Variadic template machinery.
populateChildren(std::vector<std::unique_ptr<Iterator>> &)123 inline void populateChildren(std::vector<std::unique_ptr<Iterator>> &) {}
124 template <typename... TailT>
populateChildren(std::vector<std::unique_ptr<Iterator>> & Children,std::unique_ptr<Iterator> Head,TailT...Tail)125 void populateChildren(std::vector<std::unique_ptr<Iterator>> &Children,
126 std::unique_ptr<Iterator> Head, TailT... Tail) {
127 Children.push_back(std::move(Head));
128 populateChildren(Children, std::move(Tail)...);
129 }
130 } // namespace detail
131
132 // A corpus is a set of documents, and a factory for iterators over them.
133 class Corpus {
134 DocID Size;
135
136 public:
Corpus(DocID Size)137 explicit Corpus(DocID Size) : Size(Size) {}
138
139 /// Returns AND Iterator which performs the intersection of the PostingLists
140 /// of its children.
141 ///
142 /// consume(): AND Iterator returns the product of Childrens' boosting
143 /// scores.
144 std::unique_ptr<Iterator>
145 intersect(std::vector<std::unique_ptr<Iterator>> Children) const;
146
147 /// Returns OR Iterator which performs the union of the PostingLists of its
148 /// children.
149 ///
150 /// consume(): OR Iterator returns the highest boost value among children
151 /// containing the requested item.
152 std::unique_ptr<Iterator>
153 unionOf(std::vector<std::unique_ptr<Iterator>> Children) const;
154
155 /// Returns TRUE Iterator which iterates over "virtual" PostingList
156 /// containing all items in range [0, Size) in an efficient manner.
157 std::unique_ptr<Iterator> all() const;
158
159 /// Returns FALSE Iterator which iterates over no documents.
160 std::unique_ptr<Iterator> none() const;
161
162 /// Returns BOOST iterator which multiplies the score of each item by given
163 /// factor. Boosting can be used as a computationally inexpensive filtering.
164 /// Users can return significantly more items using consumeAndBoost() and
165 /// then trim Top K using retrieval score.
166 std::unique_ptr<Iterator> boost(std::unique_ptr<Iterator> Child,
167 float Factor) const;
168
169 /// Returns LIMIT iterator, which yields up to N elements of its child
170 /// iterator. Elements only count towards the limit if they are part of the
171 /// final result set. Therefore the following iterator (AND (2) (LIMIT (1 2)
172 /// 1)) yields (2), not ().
173 std::unique_ptr<Iterator> limit(std::unique_ptr<Iterator> Child,
174 size_t Limit) const;
175
176 /// This allows intersect(create(...), create(...)) syntax.
177 template <typename... Args>
intersect(Args...args)178 std::unique_ptr<Iterator> intersect(Args... args) const {
179 std::vector<std::unique_ptr<Iterator>> Children;
180 detail::populateChildren(Children, std::forward<Args>(args)...);
181 return intersect(std::move(Children));
182 }
183
184 /// This allows unionOf(create(...), create(...)) syntax.
185 template <typename... Args>
unionOf(Args...args)186 std::unique_ptr<Iterator> unionOf(Args... args) const {
187 std::vector<std::unique_ptr<Iterator>> Children;
188 detail::populateChildren(Children, std::forward<Args>(args)...);
189 return unionOf(std::move(Children));
190 }
191 };
192
193 } // namespace dex
194 } // namespace clangd
195 } // namespace clang
196
197 #endif // LLVM_CLANG_TOOLS_EXTRA_CLANGD_INDEX_DEX_ITERATOR_H
198