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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 {
namespace {
// FIXME: Move ASTMatcher library.
AST_POLYMORPHIC_MATCHER_P(
forEachTemplateArgument,
AST_POLYMORPHIC_SUPPORTED_TYPES(ClassTemplateSpecializationDecl,
TemplateSpecializationType, FunctionDecl),
clang::ast_matchers::internal::Matcher<TemplateArgument>, InnerMatcher) {
ArrayRef<TemplateArgument> TemplateArgs =
clang::ast_matchers::internal::getTemplateSpecializationArgs(Node);
clang::ast_matchers::internal::BoundNodesTreeBuilder Result;
bool Matched = false;
for (const auto &Arg : TemplateArgs) {
clang::ast_matchers::internal::BoundNodesTreeBuilder ArgBuilder(*Builder);
if (InnerMatcher.matches(Arg, Finder, &ArgBuilder)) {
Matched = true;
Result.addMatch(ArgBuilder);
}
}
*Builder = std::move(Result);
return Matched;
}
AST_MATCHER_P(DeducedTemplateSpecializationType, refsToTemplatedDecl,
clang::ast_matchers::internal::Matcher<NamedDecl>, DeclMatcher) {
if (const auto *TD = Node.getTemplateName().getAsTemplateDecl())
return DeclMatcher.matches(*TD, Finder, Builder);
return false;
}
} // namespace
// 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(templateSpecializationType(DeclMatcher)), this);
Finder->addMatcher(loc(deducedTemplateSpecializationType(
refsToTemplatedDecl(namedDecl().bind("used")))),
this);
Finder->addMatcher(callExpr(callee(unresolvedLookupExpr().bind("used"))),
this);
Finder->addMatcher(
callExpr(hasDeclaration(functionDecl(
forEachTemplateArgument(templateArgument().bind("used"))))),
this);
Finder->addMatcher(loc(templateSpecializationType(forEachTemplateArgument(
templateArgument().bind("used")))),
this);
// Cases where we can identify the UsingShadowDecl directly, rather than
// just its target.
// FIXME: cover more cases in this way, as the AST supports it.
auto ThroughShadowMatcher = throughUsingDecl(namedDecl().bind("usedShadow"));
Finder->addMatcher(declRefExpr(ThroughShadowMatcher), this);
Finder->addMatcher(loc(usingType(ThroughShadowMatcher)), 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 a corresponding using declaration as used.
auto RemoveNamedDecl = [&](const NamedDecl *Used) {
removeFromFoundDecls(Used);
// Also remove variants of Used.
if (const auto *FD = dyn_cast<FunctionDecl>(Used)) {
removeFromFoundDecls(FD->getPrimaryTemplate());
} else if (const auto *Specialization =
dyn_cast<ClassTemplateSpecializationDecl>(Used)) {
removeFromFoundDecls(Specialization->getSpecializedTemplate());
} else if (const auto *FD = dyn_cast<FunctionDecl>(Used)) {
if (const auto *FDT = FD->getPrimaryTemplate())
removeFromFoundDecls(FDT);
} else if (const auto *ECD = dyn_cast<EnumConstantDecl>(Used)) {
if (const auto *ET = ECD->getType()->getAs<EnumType>())
removeFromFoundDecls(ET->getDecl());
}
};
// We rely on the fact that the clang AST is walked in order, usages are only
// marked after a corresponding using decl has been found.
if (const auto *Used = Result.Nodes.getNodeAs<NamedDecl>("used")) {
RemoveNamedDecl(Used);
return;
}
if (const auto *UsedShadow =
Result.Nodes.getNodeAs<UsingShadowDecl>("usedShadow")) {
removeFromFoundDecls(UsedShadow->getTargetDecl());
return;
}
if (const auto *Used = Result.Nodes.getNodeAs<TemplateArgument>("used")) {
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);
} else if (Used->getKind() == TemplateArgument::Declaration) {
RemoveNamedDecl(Used->getAsDecl());
}
return;
}
if (const auto *DRE = Result.Nodes.getNodeAs<DeclRefExpr>("used")) {
RemoveNamedDecl(DRE->getDecl());
return;
}
// 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.contains(D->getCanonicalDecl()))
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;
// Emit a fix and a fix description of the check;
diag(Context.FoundUsingDecl->getLocation(),
/*Description=*/"remove the using", DiagnosticIDs::Note)
<< FixItHint::CreateRemoval(Context.UsingDeclRange);
}
}
Contexts.clear();
}
} // namespace misc
} // namespace tidy
} // namespace clang
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