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//===--- Lookup.cpp - Framework for clang refactoring tools ---------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file defines helper methods for clang tools performing name lookup.
#include "clang/Tooling/Refactoring/Lookup.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclarationName.h"
#include "clang/Basic/SourceLocation.h"
#include "clang/Basic/SourceManager.h"
#include "llvm/ADT/SmallVector.h"
using namespace clang;
using namespace clang::tooling;
// Gets all namespaces that \p Context is in as a vector (ignoring anonymous
// namespaces). The inner namespaces come before outer namespaces in the vector.
// For example, if the context is in the following namespace:
// `namespace a { namespace b { namespace c ( ... ) } }`,
// the vector will be `{c, b, a}`.
static llvm::SmallVector<const NamespaceDecl *, 4>
getAllNamedNamespaces(const DeclContext *Context) {
llvm::SmallVector<const NamespaceDecl *, 4> Namespaces;
auto GetNextNamedNamespace = [](const DeclContext *Context) {
// Look past non-namespaces and anonymous namespaces on FromContext.
while (Context && (!isa<NamespaceDecl>(Context) ||
Context = Context->getParent();
return Context;
for (Context = GetNextNamedNamespace(Context); Context != nullptr;
Context = GetNextNamedNamespace(Context->getParent()))
return Namespaces;
// Returns true if the context in which the type is used and the context in
// which the type is declared are the same semantical namespace but different
// lexical namespaces.
static bool
usingFromDifferentCanonicalNamespace(const DeclContext *FromContext,
const DeclContext *UseContext) {
// We can skip anonymous namespace because:
// 1. `FromContext` and `UseContext` must be in the same anonymous namespaces
// since referencing across anonymous namespaces is not possible.
// 2. If `FromContext` and `UseContext` are in the same anonymous namespace,
// the function will still return `false` as expected.
llvm::SmallVector<const NamespaceDecl *, 4> FromNamespaces =
llvm::SmallVector<const NamespaceDecl *, 4> UseNamespaces =
// If `UseContext` has fewer level of nested namespaces, it cannot be in the
// same canonical namespace as the `FromContext`.
if (UseNamespaces.size() < FromNamespaces.size())
return false;
unsigned Diff = UseNamespaces.size() - FromNamespaces.size();
auto FromIter = FromNamespaces.begin();
// Only compare `FromNamespaces` with namespaces in `UseNamespaces` that can
// collide, i.e. the top N namespaces where N is the number of namespaces in
// `FromNamespaces`.
auto UseIter = UseNamespaces.begin() + Diff;
for (; FromIter != FromNamespaces.end() && UseIter != UseNamespaces.end();
++FromIter, ++UseIter) {
// Literally the same namespace, not a collision.
if (*FromIter == *UseIter)
return false;
// Now check the names. If they match we have a different canonical
// namespace with the same name.
if (cast<NamespaceDecl>(*FromIter)->getDeclName() ==
return true;
assert(FromIter == FromNamespaces.end() && UseIter == UseNamespaces.end());
return false;
static StringRef getBestNamespaceSubstr(const DeclContext *DeclA,
StringRef NewName,
bool HadLeadingColonColon) {
while (true) {
while (DeclA && !isa<NamespaceDecl>(DeclA))
DeclA = DeclA->getParent();
// Fully qualified it is! Leave :: in place if it's there already.
if (!DeclA)
return HadLeadingColonColon ? NewName : NewName.substr(2);
// Otherwise strip off redundant namespace qualifications from the new name.
// We use the fully qualified name of the namespace and remove that part
// from NewName if it has an identical prefix.
std::string NS =
"::" + cast<NamespaceDecl>(DeclA)->getQualifiedNameAsString() + "::";
if (NewName.startswith(NS))
return NewName.substr(NS.size());
// No match yet. Strip of a namespace from the end of the chain and try
// again. This allows to get optimal qualifications even if the old and new
// decl only share common namespaces at a higher level.
DeclA = DeclA->getParent();
/// Check if the name specifier begins with a written "::".
static bool isFullyQualified(const NestedNameSpecifier *NNS) {
while (NNS) {
if (NNS->getKind() == NestedNameSpecifier::Global)
return true;
NNS = NNS->getPrefix();
return false;
// Adds more scope specifier to the spelled name until the spelling is not
// ambiguous. A spelling is ambiguous if the resolution of the symbol is
// ambiguous. For example, if QName is "::y::bar", the spelling is "y::bar", and
// context contains a nested namespace "a::y", then "y::bar" can be resolved to
// ::a::y::bar in the context, which can cause compile error.
// FIXME: consider using namespaces.
static std::string disambiguateSpellingInScope(StringRef Spelling,
StringRef QName,
const DeclContext &UseContext,
SourceLocation UseLoc) {
if (Spelling.startswith("::"))
return std::string(Spelling);
auto UnspelledSpecifier = QName.drop_back(Spelling.size());
llvm::SmallVector<llvm::StringRef, 2> UnspelledScopes;
UnspelledSpecifier.split(UnspelledScopes, "::", /*MaxSplit=*/-1,
llvm::SmallVector<const NamespaceDecl *, 4> EnclosingNamespaces =
auto &AST = UseContext.getParentASTContext();
StringRef TrimmedQName = QName.substr(2);
const auto &SM = UseContext.getParentASTContext().getSourceManager();
UseLoc = SM.getSpellingLoc(UseLoc);
auto IsAmbiguousSpelling = [&](const llvm::StringRef CurSpelling) {
if (CurSpelling.startswith("::"))
return false;
// Lookup the first component of Spelling in all enclosing namespaces
// and check if there is any existing symbols with the same name but in
// different scope.
StringRef Head = CurSpelling.split("::").first;
for (const auto *NS : EnclosingNamespaces) {
auto LookupRes = NS->lookup(DeclarationName(&AST.Idents.get(Head)));
if (!LookupRes.empty()) {
for (const NamedDecl *Res : LookupRes)
// If `Res` is not visible in `UseLoc`, we don't consider it
// ambiguous. For example, a reference in a header file should not be
// affected by a potentially ambiguous name in some file that includes
// the header.
if (!TrimmedQName.startswith(Res->getQualifiedNameAsString()) &&
SM.getSpellingLoc(Res->getLocation()), UseLoc))
return true;
return false;
// Add more qualifiers until the spelling is not ambiguous.
std::string Disambiguated = std::string(Spelling);
while (IsAmbiguousSpelling(Disambiguated)) {
if (UnspelledScopes.empty()) {
Disambiguated = "::" + Disambiguated;
} else {
Disambiguated = (UnspelledScopes.back() + "::" + Disambiguated).str();
return Disambiguated;
std::string tooling::replaceNestedName(const NestedNameSpecifier *Use,
SourceLocation UseLoc,
const DeclContext *UseContext,
const NamedDecl *FromDecl,
StringRef ReplacementString) {
assert(ReplacementString.startswith("::") &&
"Expected fully-qualified name!");
// We can do a raw name replacement when we are not inside the namespace for
// the original class/function and it is not in the global namespace. The
// assumption is that outside the original namespace we must have a using
// statement that makes this work out and that other parts of this refactor
// will automatically fix using statements to point to the new class/function.
// However, if the `FromDecl` is a class forward declaration, the reference is
// still considered as referring to the original definition, so we can't do a
// raw name replacement in this case.
const bool class_name_only = !Use;
const bool in_global_namespace =
const bool is_class_forward_decl =
isa<CXXRecordDecl>(FromDecl) &&
if (class_name_only && !in_global_namespace && !is_class_forward_decl &&
UseContext)) {
auto Pos = ReplacementString.rfind("::");
return std::string(Pos != StringRef::npos
? ReplacementString.substr(Pos + 2)
: ReplacementString);
// We did not match this because of a using statement, so we will need to
// figure out how good a namespace match we have with our destination type.
// We work backwards (from most specific possible namespace to least
// specific).
StringRef Suggested = getBestNamespaceSubstr(UseContext, ReplacementString,
return disambiguateSpellingInScope(Suggested, ReplacementString, *UseContext,