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"
21using namespace clang;
22using 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}`.
29static llvm::SmallVector<const NamespaceDecl *, 4>
30getAllNamedNamespaces(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>(Val: Context) ||
35 cast<NamespaceDecl>(Val: 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(Elt: cast<NamespaceDecl>(Val: 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.
48static bool
49usingFromDifferentCanonicalNamespace(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(Context: FromContext);
58 llvm::SmallVector<const NamespaceDecl *, 4> UseNamespaces =
59 getAllNamedNamespaces(Context: 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>(Val: *FromIter)->getDeclName() ==
78 cast<NamespaceDecl>(Val: *UseIter)->getDeclName())
79 return true;
80 }
81 assert(FromIter == FromNamespaces.end() && UseIter == UseNamespaces.end());
82 return false;
83}
84
85static StringRef getBestNamespaceSubstr(const DeclContext *DeclA,
86 StringRef NewName,
87 bool HadLeadingColonColon) {
88 while (true) {
89 while (DeclA && !isa<NamespaceDecl>(Val: 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(Start: 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>(Val: DeclA)->getQualifiedNameAsString() + "::";
101 if (NewName.consume_front(Prefix: NS))
102 return NewName;
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 "::".
112static 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.
127static std::string disambiguateSpellingInScope(StringRef Spelling,
128 StringRef QName,
129 const DeclContext &UseContext,
130 SourceLocation UseLoc) {
131 assert(QName.starts_with("::"));
132 assert(QName.ends_with(Spelling));
133 if (Spelling.starts_with(Prefix: "::"))
134 return std::string(Spelling);
135
136 auto UnspelledSpecifier = QName.drop_back(N: Spelling.size());
137 llvm::SmallVector<llvm::StringRef, 2> UnspelledScopes;
138 UnspelledSpecifier.split(A&: UnspelledScopes, Separator: "::", /*MaxSplit=*/-1,
139 /*KeepEmpty=*/false);
140
141 llvm::SmallVector<const NamespaceDecl *, 4> EnclosingNamespaces =
142 getAllNamedNamespaces(Context: &UseContext);
143 auto &AST = UseContext.getParentASTContext();
144 StringRef TrimmedQName = QName.substr(Start: 2);
145 const auto &SM = UseContext.getParentASTContext().getSourceManager();
146 UseLoc = SM.getSpellingLoc(Loc: UseLoc);
147
148 auto IsAmbiguousSpelling = [&](const llvm::StringRef CurSpelling) {
149 if (CurSpelling.starts_with(Prefix: "::"))
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(Separator: "::").first;
155 for (const auto *NS : EnclosingNamespaces) {
156 auto LookupRes = NS->lookup(Name: DeclarationName(&AST.Idents.get(Name: 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.starts_with(Prefix: Res->getQualifiedNameAsString()) &&
164 SM.isBeforeInTranslationUnit(
165 LHS: SM.getSpellingLoc(Loc: Res->getLocation()), RHS: 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
185std::string tooling::replaceNestedName(const NestedNameSpecifier *Use,
186 SourceLocation UseLoc,
187 const DeclContext *UseContext,
188 const NamedDecl *FromDecl,
189 StringRef ReplacementString) {
190 assert(ReplacementString.starts_with("::") &&
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>(Val: FromDecl->getDeclContext());
204 const bool is_class_forward_decl =
205 isa<CXXRecordDecl>(Val: FromDecl) &&
206 !cast<CXXRecordDecl>(Val: FromDecl)->isCompleteDefinition();
207 if (class_name_only && !in_global_namespace && !is_class_forward_decl &&
208 !usingFromDifferentCanonicalNamespace(FromContext: FromDecl->getDeclContext(),
209 UseContext)) {
210 auto Pos = ReplacementString.rfind(Str: "::");
211 return std::string(Pos != StringRef::npos
212 ? ReplacementString.substr(Start: 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(DeclA: UseContext, NewName: ReplacementString,
220 HadLeadingColonColon: isFullyQualified(NNS: Use));
221
222 return disambiguateSpellingInScope(Spelling: Suggested, QName: ReplacementString, UseContext: *UseContext,
223 UseLoc);
224}
225