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//===--- UnusedUsingDeclsCheck.cpp - clang-tidy----------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "UnusedUsingDeclsCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "clang/Lex/Lexer.h"
using namespace clang::ast_matchers;
namespace clang {
namespace tidy {
namespace misc {
// A function that helps to tell whether a TargetDecl in a UsingDecl will be
// checked. Only variable, function, function template, class template, class,
// enum declaration and enum constant declaration are considered.
static bool ShouldCheckDecl(const Decl *TargetDecl) {
return isa<RecordDecl>(TargetDecl) || isa<ClassTemplateDecl>(TargetDecl) ||
isa<FunctionDecl>(TargetDecl) || isa<VarDecl>(TargetDecl) ||
isa<FunctionTemplateDecl>(TargetDecl) || isa<EnumDecl>(TargetDecl) ||
isa<EnumConstantDecl>(TargetDecl);
}
void UnusedUsingDeclsCheck::registerMatchers(MatchFinder *Finder) {
Finder->addMatcher(usingDecl(isExpansionInMainFile()).bind("using"), this);
auto DeclMatcher = hasDeclaration(namedDecl().bind("used"));
Finder->addMatcher(loc(enumType(DeclMatcher)), this);
Finder->addMatcher(loc(recordType(DeclMatcher)), this);
Finder->addMatcher(loc(templateSpecializationType(DeclMatcher)), this);
Finder->addMatcher(declRefExpr().bind("used"), this);
Finder->addMatcher(callExpr(callee(unresolvedLookupExpr().bind("used"))),
this);
Finder->addMatcher(
callExpr(hasDeclaration(functionDecl(hasAnyTemplateArgument(
anyOf(refersToTemplate(templateName().bind("used")),
refersToDeclaration(functionDecl().bind("used"))))))),
this);
Finder->addMatcher(loc(templateSpecializationType(hasAnyTemplateArgument(
templateArgument().bind("used")))),
this);
}
void UnusedUsingDeclsCheck::check(const MatchFinder::MatchResult &Result) {
if (Result.Context->getDiagnostics().hasUncompilableErrorOccurred())
return;
if (const auto *Using = Result.Nodes.getNodeAs<UsingDecl>("using")) {
// Ignores using-declarations defined in macros.
if (Using->getLocation().isMacroID())
return;
// Ignores using-declarations defined in class definition.
if (isa<CXXRecordDecl>(Using->getDeclContext()))
return;
// FIXME: We ignore using-decls defined in function definitions at the
// moment because of false positives caused by ADL and different function
// scopes.
if (isa<FunctionDecl>(Using->getDeclContext()))
return;
UsingDeclContext Context(Using);
Context.UsingDeclRange = CharSourceRange::getCharRange(
Using->getBeginLoc(),
Lexer::findLocationAfterToken(
Using->getEndLoc(), tok::semi, *Result.SourceManager, getLangOpts(),
/*SkipTrailingWhitespaceAndNewLine=*/true));
for (const auto *UsingShadow : Using->shadows()) {
const auto *TargetDecl = UsingShadow->getTargetDecl()->getCanonicalDecl();
if (ShouldCheckDecl(TargetDecl))
Context.UsingTargetDecls.insert(TargetDecl);
}
if (!Context.UsingTargetDecls.empty())
Contexts.push_back(Context);
return;
}
// Mark using declarations as used by setting FoundDecls' value to zero. As
// the AST is walked in order, usages are only marked after a the
// corresponding using declaration has been found.
// FIXME: This currently doesn't look at whether the type reference is
// actually found with the help of the using declaration.
if (const auto *Used = Result.Nodes.getNodeAs<NamedDecl>("used")) {
if (const auto *FD = dyn_cast<FunctionDecl>(Used)) {
removeFromFoundDecls(FD->getPrimaryTemplate());
} else if (const auto *Specialization =
dyn_cast<ClassTemplateSpecializationDecl>(Used)) {
Used = Specialization->getSpecializedTemplate();
}
removeFromFoundDecls(Used);
return;
}
if (const auto *Used = Result.Nodes.getNodeAs<TemplateArgument>("used")) {
// FIXME: Support non-type template parameters.
if (Used->getKind() == TemplateArgument::Template) {
if (const auto *TD = Used->getAsTemplate().getAsTemplateDecl())
removeFromFoundDecls(TD);
} else if (Used->getKind() == TemplateArgument::Type) {
if (auto *RD = Used->getAsType()->getAsCXXRecordDecl())
removeFromFoundDecls(RD);
}
return;
}
if (const auto *Used = Result.Nodes.getNodeAs<TemplateName>("used")) {
removeFromFoundDecls(Used->getAsTemplateDecl());
return;
}
if (const auto *DRE = Result.Nodes.getNodeAs<DeclRefExpr>("used")) {
if (const auto *FD = dyn_cast<FunctionDecl>(DRE->getDecl())) {
if (const auto *FDT = FD->getPrimaryTemplate())
removeFromFoundDecls(FDT);
else
removeFromFoundDecls(FD);
} else if (const auto *VD = dyn_cast<VarDecl>(DRE->getDecl())) {
removeFromFoundDecls(VD);
} else if (const auto *ECD = dyn_cast<EnumConstantDecl>(DRE->getDecl())) {
removeFromFoundDecls(ECD);
if (const auto *ET = ECD->getType()->getAs<EnumType>())
removeFromFoundDecls(ET->getDecl());
}
}
// Check the uninstantiated template function usage.
if (const auto *ULE = Result.Nodes.getNodeAs<UnresolvedLookupExpr>("used")) {
for (const NamedDecl *ND : ULE->decls()) {
if (const auto *USD = dyn_cast<UsingShadowDecl>(ND))
removeFromFoundDecls(USD->getTargetDecl()->getCanonicalDecl());
}
}
}
void UnusedUsingDeclsCheck::removeFromFoundDecls(const Decl *D) {
if (!D)
return;
// FIXME: Currently, we don't handle the using-decls being used in different
// scopes (such as different namespaces, different functions). Instead of
// giving an incorrect message, we mark all of them as used.
//
// FIXME: Use a more efficient way to find a matching context.
for (auto &Context : Contexts) {
if (Context.UsingTargetDecls.count(D->getCanonicalDecl()) > 0)
Context.IsUsed = true;
}
}
void UnusedUsingDeclsCheck::onEndOfTranslationUnit() {
for (const auto &Context : Contexts) {
if (!Context.IsUsed) {
diag(Context.FoundUsingDecl->getLocation(), "using decl %0 is unused")
<< Context.FoundUsingDecl
<< FixItHint::CreateRemoval(Context.UsingDeclRange);
}
}
Contexts.clear();
}
} // namespace misc
} // namespace tidy
} // namespace clang
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