clang-tools  10.0.0
FileDistance.cpp
Go to the documentation of this file.
1 //===--- FileDistance.cpp - File contents container -------------*- 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 // The FileDistance structure allows calculating the minimum distance to paths
10 // in a single tree.
11 // We simply walk up the path's ancestors until we find a node whose cost is
12 // known, and add the cost of walking back down. Initialization ensures this
13 // gives the correct path to the roots.
14 // We cache the results, so that the runtime is O(|A|), where A is the set of
15 // all distinct ancestors of visited paths.
16 //
17 // Example after initialization with /=2, /bar=0, DownCost = 1:
18 // / = 2
19 // /bar = 0
20 //
21 // After querying /foo/bar and /bar/foo:
22 // / = 2
23 // /bar = 0
24 // /bar/foo = 1
25 // /foo = 3
26 // /foo/bar = 4
27 //
28 // URIDistance creates FileDistance lazily for each URI scheme encountered. In
29 // practice this is a small constant factor.
30 //
31 //===-------------------------------------------------------------------------//
32 
33 #include "FileDistance.h"
34 #include "Logger.h"
35 #include "llvm/ADT/STLExtras.h"
36 #include <queue>
37 
38 namespace clang {
39 namespace clangd {
40 
41 // Convert a path into the canonical form.
42 // Canonical form is either "/", or "/segment" * N:
43 // C:\foo\bar --> /c:/foo/bar
44 // /foo/ --> /foo
45 // a/b/c --> /a/b/c
46 static llvm::SmallString<128> canonicalize(llvm::StringRef Path) {
47  llvm::SmallString<128> Result = Path.rtrim('/');
48  native(Result, llvm::sys::path::Style::posix);
49  if (Result.empty() || Result.front() != '/')
50  Result.insert(Result.begin(), '/');
51  return Result;
52 }
53 
54 constexpr const unsigned FileDistance::Unreachable;
55 const llvm::hash_code FileDistance::RootHash =
56  llvm::hash_value(llvm::StringRef("/"));
57 
58 FileDistance::FileDistance(llvm::StringMap<SourceParams> Sources,
59  const FileDistanceOptions &Opts)
60  : Opts(Opts) {
61  llvm::DenseMap<llvm::hash_code, llvm::SmallVector<llvm::hash_code, 4>>
62  DownEdges;
63  // Compute the best distance following only up edges.
64  // Keep track of down edges, in case we can use them to improve on this.
65  for (const auto &S : Sources) {
66  auto Canonical = canonicalize(S.getKey());
67  dlog("Source {0} = {1}, MaxUp = {2}", Canonical, S.second.Cost,
68  S.second.MaxUpTraversals);
69  // Walk up to ancestors of this source, assigning cost.
70  llvm::StringRef Rest = Canonical;
71  llvm::hash_code Hash = llvm::hash_value(Rest);
72  for (unsigned I = 0; !Rest.empty(); ++I) {
73  Rest = parent_path(Rest, llvm::sys::path::Style::posix);
74  auto NextHash = llvm::hash_value(Rest);
75  auto &Down = DownEdges[NextHash];
76  if (!llvm::is_contained(Down, Hash))
77  Down.push_back(Hash);
78  // We can't just break after MaxUpTraversals, must still set DownEdges.
79  if (I > S.getValue().MaxUpTraversals) {
80  if (Cache.find(Hash) != Cache.end())
81  break;
82  } else {
83  unsigned Cost = S.getValue().Cost + I * Opts.UpCost;
84  auto R = Cache.try_emplace(Hash, Cost);
85  if (!R.second) {
86  if (Cost < R.first->second) {
87  R.first->second = Cost;
88  } else {
89  // If we're not the best way to get to this path, stop assigning.
90  break;
91  }
92  }
93  }
94  Hash = NextHash;
95  }
96  }
97  // Now propagate scores parent -> child if that's an improvement.
98  // BFS ensures we propagate down chains (must visit parents before children).
99  std::queue<llvm::hash_code> Next;
100  for (auto Child : DownEdges.lookup(llvm::hash_value(llvm::StringRef(""))))
101  Next.push(Child);
102  while (!Next.empty()) {
103  auto Parent = Next.front();
104  Next.pop();
105  auto ParentCost = Cache.lookup(Parent);
106  for (auto Child : DownEdges.lookup(Parent)) {
107  if (Parent != RootHash || Opts.AllowDownTraversalFromRoot) {
108  auto &ChildCost =
109  Cache.try_emplace(Child, Unreachable).first->getSecond();
110  if (ParentCost + Opts.DownCost < ChildCost)
111  ChildCost = ParentCost + Opts.DownCost;
112  }
113  Next.push(Child);
114  }
115  }
116 }
117 
118 unsigned FileDistance::distance(llvm::StringRef Path) {
119  auto Canonical = canonicalize(Path);
120  unsigned Cost = Unreachable;
121  llvm::SmallVector<llvm::hash_code, 16> Ancestors;
122  // Walk up ancestors until we find a path we know the distance for.
123  for (llvm::StringRef Rest = Canonical; !Rest.empty();
124  Rest = parent_path(Rest, llvm::sys::path::Style::posix)) {
125  auto Hash = llvm::hash_value(Rest);
126  if (Hash == RootHash && !Ancestors.empty() &&
128  Cost = Unreachable;
129  break;
130  }
131  auto It = Cache.find(Hash);
132  if (It != Cache.end()) {
133  Cost = It->second;
134  break;
135  }
136  Ancestors.push_back(Hash);
137  }
138  // Now we know the costs for (known node, queried node].
139  // Fill these in, walking down the directory tree.
140  for (llvm::hash_code Hash : llvm::reverse(Ancestors)) {
141  if (Cost != Unreachable)
142  Cost += Opts.DownCost;
143  Cache.try_emplace(Hash, Cost);
144  }
145  dlog("distance({0} = {1})", Path, Cost);
146  return Cost;
147 }
148 
149 unsigned URIDistance::distance(llvm::StringRef URI) {
150  auto R = Cache.try_emplace(llvm::hash_value(URI), FileDistance::Unreachable);
151  if (!R.second)
152  return R.first->getSecond();
153  if (auto U = clangd::URI::parse(URI)) {
154  dlog("distance({0} = {1})", URI, U->body());
155  R.first->second = forScheme(U->scheme()).distance(U->body());
156  } else {
157  log("URIDistance::distance() of unparseable {0}: {1}", URI, U.takeError());
158  }
159  return R.first->second;
160 }
161 
162 FileDistance &URIDistance::forScheme(llvm::StringRef Scheme) {
163  auto &Delegate = ByScheme[Scheme];
164  if (!Delegate) {
165  llvm::StringMap<SourceParams> SchemeSources;
166  for (const auto &Source : Sources) {
167  if (auto U = clangd::URI::create(Source.getKey(), Scheme))
168  SchemeSources.try_emplace(U->body(), Source.getValue());
169  else
170  llvm::consumeError(U.takeError());
171  }
172  dlog("FileDistance for scheme {0}: {1}/{2} sources", Scheme,
173  SchemeSources.size(), Sources.size());
174  Delegate.reset(new FileDistance(std::move(SchemeSources), Opts));
175  }
176  return *Delegate;
177 }
178 
179 static std::pair<std::string, int> scopeToPath(llvm::StringRef Scope) {
180  llvm::SmallVector<llvm::StringRef, 4> Split;
181  Scope.split(Split, "::", /*MaxSplit=*/-1, /*KeepEmpty=*/false);
182  return {"/" + llvm::join(Split, "/"), Split.size()};
183 }
184 
185 static FileDistance
186 createScopeFileDistance(llvm::ArrayRef<std::string> QueryScopes) {
187  FileDistanceOptions Opts;
188  Opts.UpCost = 2;
189  Opts.DownCost = 4;
190  Opts.AllowDownTraversalFromRoot = false;
191 
192  llvm::StringMap<SourceParams> Sources;
193  llvm::StringRef Preferred =
194  QueryScopes.empty() ? "" : QueryScopes.front().c_str();
195  for (llvm::StringRef S : QueryScopes) {
196  SourceParams Param;
197  // Penalize the global scope even it's preferred, as all projects can define
198  // symbols in it, and there is pattern where using-namespace is used in
199  // place of enclosing namespaces (e.g. in implementation files).
200  if (S == Preferred)
201  Param.Cost = S == "" ? 4 : 0;
202  else if (Preferred.startswith(S) && !S.empty())
203  continue; // just rely on up-traversals.
204  else
205  Param.Cost = S == "" ? 6 : 2;
206  auto Path = scopeToPath(S);
207  // The global namespace is not 'near' its children.
208  Param.MaxUpTraversals = std::max(Path.second - 1, 0);
209  Sources[Path.first] = std::move(Param);
210  }
211  return FileDistance(std::move(Sources), Opts);
212 }
213 
214 ScopeDistance::ScopeDistance(llvm::ArrayRef<std::string> QueryScopes)
215  : Distance(createScopeFileDistance(QueryScopes)) {}
216 
217 unsigned ScopeDistance::distance(llvm::StringRef SymbolScope) {
218  return Distance.distance(scopeToPath(SymbolScope).first);
219 }
220 
221 } // namespace clangd
222 } // namespace clang
ScopeDistance(llvm::ArrayRef< std::string > QueryScopes)
QueryScopes[0] is the preferred scope.
unsigned distance(llvm::StringRef SymbolScope)
const Node * Parent
static std::pair< std::string, int > scopeToPath(llvm::StringRef Scope)
static constexpr unsigned Unreachable
Definition: FileDistance.h:74
void log(const char *Fmt, Ts &&... Vals)
Definition: Logger.h:62
std::string Path
A typedef to represent a file path.
Definition: Path.h:20
#define dlog(...)
Definition: Logger.h:72
static llvm::SmallString< 128 > canonicalize(llvm::StringRef Path)
FileDistance(llvm::StringMap< SourceParams > Sources, const FileDistanceOptions &Opts={})
unsigned distance(llvm::StringRef URI)
static llvm::Expected< URI > create(llvm::StringRef AbsolutePath, llvm::StringRef Scheme)
Creates a URI for a file in the given scheme.
Definition: URI.cpp:197
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//
static FileDistance createScopeFileDistance(llvm::ArrayRef< std::string > QueryScopes)
A URI describes the location of a source file.
Definition: URI.h:28
llvm::hash_code hash_value(const SymbolID &ID)
Definition: SymbolID.cpp:50
static llvm::Expected< URI > parse(llvm::StringRef Uri)
Parse a URI string "<scheme>:[//<authority>/]<path>".
Definition: URI.cpp:164
static std::string join(ArrayRef< SpecialMemberFunctionsCheck::SpecialMemberFunctionKind > SMFS, llvm::StringRef AndOr)
unsigned distance(llvm::StringRef Path)
static const llvm::hash_code RootHash
Definition: FileDistance.h:75