clang  12.0.0git
Lookup.cpp
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1 //===--- Lookup.cpp - Framework for clang refactoring tools ---------------===//
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 defines helper methods for clang tools performing name lookup.
10 //
11 //===----------------------------------------------------------------------===//
12 
14 #include "clang/AST/ASTContext.h"
15 #include "clang/AST/Decl.h"
16 #include "clang/AST/DeclCXX.h"
20 #include "llvm/ADT/SmallVector.h"
21 using namespace clang;
22 using namespace clang::tooling;
23 
24 // Gets all namespaces that \p Context is in as a vector (ignoring anonymous
25 // namespaces). The inner namespaces come before outer namespaces in the vector.
26 // For example, if the context is in the following namespace:
27 // `namespace a { namespace b { namespace c ( ... ) } }`,
28 // the vector will be `{c, b, a}`.
32  auto GetNextNamedNamespace = [](const DeclContext *Context) {
33  // Look past non-namespaces and anonymous namespaces on FromContext.
34  while (Context && (!isa<NamespaceDecl>(Context) ||
35  cast<NamespaceDecl>(Context)->isAnonymousNamespace()))
36  Context = Context->getParent();
37  return Context;
38  };
39  for (Context = GetNextNamedNamespace(Context); Context != nullptr;
40  Context = GetNextNamedNamespace(Context->getParent()))
41  Namespaces.push_back(cast<NamespaceDecl>(Context));
42  return Namespaces;
43 }
44 
45 // Returns true if the context in which the type is used and the context in
46 // which the type is declared are the same semantical namespace but different
47 // lexical namespaces.
48 static bool
50  const DeclContext *UseContext) {
51  // We can skip anonymous namespace because:
52  // 1. `FromContext` and `UseContext` must be in the same anonymous namespaces
53  // since referencing across anonymous namespaces is not possible.
54  // 2. If `FromContext` and `UseContext` are in the same anonymous namespace,
55  // the function will still return `false` as expected.
57  getAllNamedNamespaces(FromContext);
59  getAllNamedNamespaces(UseContext);
60  // If `UseContext` has fewer level of nested namespaces, it cannot be in the
61  // same canonical namespace as the `FromContext`.
62  if (UseNamespaces.size() < FromNamespaces.size())
63  return false;
64  unsigned Diff = UseNamespaces.size() - FromNamespaces.size();
65  auto FromIter = FromNamespaces.begin();
66  // Only compare `FromNamespaces` with namespaces in `UseNamespaces` that can
67  // collide, i.e. the top N namespaces where N is the number of namespaces in
68  // `FromNamespaces`.
69  auto UseIter = UseNamespaces.begin() + Diff;
70  for (; FromIter != FromNamespaces.end() && UseIter != UseNamespaces.end();
71  ++FromIter, ++UseIter) {
72  // Literally the same namespace, not a collision.
73  if (*FromIter == *UseIter)
74  return false;
75  // Now check the names. If they match we have a different canonical
76  // namespace with the same name.
77  if (cast<NamespaceDecl>(*FromIter)->getDeclName() ==
78  cast<NamespaceDecl>(*UseIter)->getDeclName())
79  return true;
80  }
81  assert(FromIter == FromNamespaces.end() && UseIter == UseNamespaces.end());
82  return false;
83 }
84 
85 static StringRef getBestNamespaceSubstr(const DeclContext *DeclA,
86  StringRef NewName,
87  bool HadLeadingColonColon) {
88  while (true) {
89  while (DeclA && !isa<NamespaceDecl>(DeclA))
90  DeclA = DeclA->getParent();
91 
92  // Fully qualified it is! Leave :: in place if it's there already.
93  if (!DeclA)
94  return HadLeadingColonColon ? NewName : NewName.substr(2);
95 
96  // Otherwise strip off redundant namespace qualifications from the new name.
97  // We use the fully qualified name of the namespace and remove that part
98  // from NewName if it has an identical prefix.
99  std::string NS =
100  "::" + cast<NamespaceDecl>(DeclA)->getQualifiedNameAsString() + "::";
101  if (NewName.startswith(NS))
102  return NewName.substr(NS.size());
103 
104  // No match yet. Strip of a namespace from the end of the chain and try
105  // again. This allows to get optimal qualifications even if the old and new
106  // decl only share common namespaces at a higher level.
107  DeclA = DeclA->getParent();
108  }
109 }
110 
111 /// Check if the name specifier begins with a written "::".
112 static bool isFullyQualified(const NestedNameSpecifier *NNS) {
113  while (NNS) {
114  if (NNS->getKind() == NestedNameSpecifier::Global)
115  return true;
116  NNS = NNS->getPrefix();
117  }
118  return false;
119 }
120 
121 // Adds more scope specifier to the spelled name until the spelling is not
122 // ambiguous. A spelling is ambiguous if the resolution of the symbol is
123 // ambiguous. For example, if QName is "::y::bar", the spelling is "y::bar", and
124 // context contains a nested namespace "a::y", then "y::bar" can be resolved to
125 // ::a::y::bar in the context, which can cause compile error.
126 // FIXME: consider using namespaces.
127 static std::string disambiguateSpellingInScope(StringRef Spelling,
128  StringRef QName,
129  const DeclContext &UseContext,
130  SourceLocation UseLoc) {
131  assert(QName.startswith("::"));
132  assert(QName.endswith(Spelling));
133  if (Spelling.startswith("::"))
134  return std::string(Spelling);
135 
136  auto UnspelledSpecifier = QName.drop_back(Spelling.size());
138  UnspelledSpecifier.split(UnspelledScopes, "::", /*MaxSplit=*/-1,
139  /*KeepEmpty=*/false);
140 
141  llvm::SmallVector<const NamespaceDecl *, 4> EnclosingNamespaces =
142  getAllNamedNamespaces(&UseContext);
143  auto &AST = UseContext.getParentASTContext();
144  StringRef TrimmedQName = QName.substr(2);
145  const auto &SM = UseContext.getParentASTContext().getSourceManager();
146  UseLoc = SM.getSpellingLoc(UseLoc);
147 
148  auto IsAmbiguousSpelling = [&](const llvm::StringRef CurSpelling) {
149  if (CurSpelling.startswith("::"))
150  return false;
151  // Lookup the first component of Spelling in all enclosing namespaces
152  // and check if there is any existing symbols with the same name but in
153  // different scope.
154  StringRef Head = CurSpelling.split("::").first;
155  for (const auto *NS : EnclosingNamespaces) {
156  auto LookupRes = NS->lookup(DeclarationName(&AST.Idents.get(Head)));
157  if (!LookupRes.empty()) {
158  for (const NamedDecl *Res : LookupRes)
159  // If `Res` is not visible in `UseLoc`, we don't consider it
160  // ambiguous. For example, a reference in a header file should not be
161  // affected by a potentially ambiguous name in some file that includes
162  // the header.
163  if (!TrimmedQName.startswith(Res->getQualifiedNameAsString()) &&
164  SM.isBeforeInTranslationUnit(
165  SM.getSpellingLoc(Res->getLocation()), UseLoc))
166  return true;
167  }
168  }
169  return false;
170  };
171 
172  // Add more qualifiers until the spelling is not ambiguous.
173  std::string Disambiguated = std::string(Spelling);
174  while (IsAmbiguousSpelling(Disambiguated)) {
175  if (UnspelledScopes.empty()) {
176  Disambiguated = "::" + Disambiguated;
177  } else {
178  Disambiguated = (UnspelledScopes.back() + "::" + Disambiguated).str();
179  UnspelledScopes.pop_back();
180  }
181  }
182  return Disambiguated;
183 }
184 
186  SourceLocation UseLoc,
187  const DeclContext *UseContext,
188  const NamedDecl *FromDecl,
189  StringRef ReplacementString) {
190  assert(ReplacementString.startswith("::") &&
191  "Expected fully-qualified name!");
192 
193  // We can do a raw name replacement when we are not inside the namespace for
194  // the original class/function and it is not in the global namespace. The
195  // assumption is that outside the original namespace we must have a using
196  // statement that makes this work out and that other parts of this refactor
197  // will automatically fix using statements to point to the new class/function.
198  // However, if the `FromDecl` is a class forward declaration, the reference is
199  // still considered as referring to the original definition, so we can't do a
200  // raw name replacement in this case.
201  const bool class_name_only = !Use;
202  const bool in_global_namespace =
203  isa<TranslationUnitDecl>(FromDecl->getDeclContext());
204  const bool is_class_forward_decl =
205  isa<CXXRecordDecl>(FromDecl) &&
206  !cast<CXXRecordDecl>(FromDecl)->isCompleteDefinition();
207  if (class_name_only && !in_global_namespace && !is_class_forward_decl &&
209  UseContext)) {
210  auto Pos = ReplacementString.rfind("::");
211  return std::string(Pos != StringRef::npos
212  ? ReplacementString.substr(Pos + 2)
213  : ReplacementString);
214  }
215  // We did not match this because of a using statement, so we will need to
216  // figure out how good a namespace match we have with our destination type.
217  // We work backwards (from most specific possible namespace to least
218  // specific).
219  StringRef Suggested = getBestNamespaceSubstr(UseContext, ReplacementString,
220  isFullyQualified(Use));
221 
222  return disambiguateSpellingInScope(Suggested, ReplacementString, *UseContext,
223  UseLoc);
224 }
Defines the clang::ASTContext interface.
std::string replaceNestedName(const NestedNameSpecifier *Use, SourceLocation UseLoc, const DeclContext *UseContext, const NamedDecl *FromDecl, StringRef ReplacementString)
Emulate a lookup to replace one nested name specifier with another using as few additional namespace ...
Definition: Lookup.cpp:185
Defines the SourceManager interface.
static std::string disambiguateSpellingInScope(StringRef Spelling, StringRef QName, const DeclContext &UseContext, SourceLocation UseLoc)
Definition: Lookup.cpp:127
NestedNameSpecifier * getPrefix() const
Return the prefix of this nested name specifier.
static bool isFullyQualified(const NestedNameSpecifier *NNS)
Check if the name specifier begins with a written "::".
Definition: Lookup.cpp:112
SpecifierKind getKind() const
Determine what kind of nested name specifier is stored.
static StringRef getBestNamespaceSubstr(const DeclContext *DeclA, StringRef NewName, bool HadLeadingColonColon)
Definition: Lookup.cpp:85
DeclContext * getDeclContext()
Definition: DeclBase.h:439
static llvm::SmallVector< const NamespaceDecl *, 4 > getAllNamedNamespaces(const DeclContext *Context)
Definition: Lookup.cpp:30
DeclContext * getParent()
getParent - Returns the containing DeclContext.
Definition: DeclBase.h:1816
#define SM(sm)
Definition: Cuda.cpp:62
const NamedDecl * FromDecl
Encodes a location in the source.
Represents a C++ nested name specifier, such as "\::std::vector<int>::".
Dataflow Directional Tag Classes.
DeclContext - This is used only as base class of specific decl types that can act as declaration cont...
Definition: DeclBase.h:1303
The name of a declaration.
static bool usingFromDifferentCanonicalNamespace(const DeclContext *FromContext, const DeclContext *UseContext)
Definition: Lookup.cpp:49
SourceManager & getSourceManager()
Definition: ASTContext.h:619
Defines the C++ Decl subclasses, other than those for templates (found in DeclTemplate.h) and friends (in DeclFriend.h).
Defines the clang::SourceLocation class and associated facilities.
ASTContext & getParentASTContext() const
Definition: DeclBase.h:1845
This represents a decl that may have a name.
Definition: Decl.h:223
The global specifier &#39;::&#39;. There is no stored value.