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 
13 #include "clang/Tooling/Refactoring/Lookup.h"
14 #include "clang/AST/ASTContext.h"
15 #include "clang/AST/Decl.h"
16 #include "clang/AST/DeclCXX.h"
17 #include "clang/AST/DeclarationName.h"
18 #include "clang/Basic/SourceLocation.h"
19 #include "clang/Basic/SourceManager.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}`.
29 static llvm::SmallVector<const NamespaceDecl *, 4>
30 getAllNamedNamespaces(const DeclContext *Context) {
31   llvm::SmallVector<const NamespaceDecl *, 4> Namespaces;
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
49 usingFromDifferentCanonicalNamespace(const DeclContext *FromContext,
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.
56   llvm::SmallVector<const NamespaceDecl *, 4> FromNamespaces =
57       getAllNamedNamespaces(FromContext);
58   llvm::SmallVector<const NamespaceDecl *, 4> UseNamespaces =
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());
137   llvm::SmallVector<llvm::StringRef, 2> UnspelledScopes;
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 
185 std::string tooling::replaceNestedName(const NestedNameSpecifier *Use,
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 &&
208       !usingFromDifferentCanonicalNamespace(FromDecl->getDeclContext(),
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 }
225