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//===--- UnnecessaryCopyInitialization.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 "UnnecessaryCopyInitialization.h"
#include "../utils/DeclRefExprUtils.h"
#include "../utils/FixItHintUtils.h"
#include "../utils/Matchers.h"
#include "../utils/OptionsUtils.h"
namespace clang {
namespace tidy {
namespace performance {
namespace {
void recordFixes(const VarDecl &Var, ASTContext &Context,
DiagnosticBuilder &Diagnostic) {
Diagnostic << utils::fixit::changeVarDeclToReference(Var, Context);
if (!Var.getType().isLocalConstQualified())
Diagnostic << utils::fixit::changeVarDeclToConst(Var);
}
} // namespace
using namespace ::clang::ast_matchers;
using utils::decl_ref_expr::isOnlyUsedAsConst;
UnnecessaryCopyInitialization::UnnecessaryCopyInitialization(
StringRef Name, ClangTidyContext *Context)
: ClangTidyCheck(Name, Context),
AllowedTypes(
utils::options::parseStringList(Options.get("AllowedTypes", ""))) {}
void UnnecessaryCopyInitialization::registerMatchers(MatchFinder *Finder) {
auto ConstReference = referenceType(pointee(qualType(isConstQualified())));
// Match method call expressions where the `this` argument is only used as
// const, this will be checked in `check()` part. This returned const
// reference is highly likely to outlive the local const reference of the
// variable being declared. The assumption is that the const reference being
// returned either points to a global static variable or to a member of the
// called object.
auto ConstRefReturningMethodCall =
cxxMemberCallExpr(callee(cxxMethodDecl(returns(ConstReference))),
on(declRefExpr(to(varDecl().bind("objectArg")))));
auto ConstRefReturningFunctionCall =
callExpr(callee(functionDecl(returns(ConstReference))),
unless(callee(cxxMethodDecl())));
auto localVarCopiedFrom = [this](const internal::Matcher<Expr> &CopyCtorArg) {
return compoundStmt(
forEachDescendant(
declStmt(
has(varDecl(hasLocalStorage(),
hasType(qualType(
hasCanonicalType(
matchers::isExpensiveToCopy()),
unless(hasDeclaration(namedDecl(
matchers::matchesAnyListedName(
AllowedTypes)))))),
unless(isImplicit()),
hasInitializer(
cxxConstructExpr(
hasDeclaration(cxxConstructorDecl(
isCopyConstructor())),
hasArgument(0, CopyCtorArg))
.bind("ctorCall")))
.bind("newVarDecl")))
.bind("declStmt")))
.bind("blockStmt");
};
Finder->addMatcher(localVarCopiedFrom(anyOf(ConstRefReturningFunctionCall,
ConstRefReturningMethodCall)),
this);
Finder->addMatcher(localVarCopiedFrom(declRefExpr(
to(varDecl(hasLocalStorage()).bind("oldVarDecl")))),
this);
}
void UnnecessaryCopyInitialization::check(
const MatchFinder::MatchResult &Result) {
const auto *NewVar = Result.Nodes.getNodeAs<VarDecl>("newVarDecl");
const auto *OldVar = Result.Nodes.getNodeAs<VarDecl>("oldVarDecl");
const auto *ObjectArg = Result.Nodes.getNodeAs<VarDecl>("objectArg");
const auto *BlockStmt = Result.Nodes.getNodeAs<Stmt>("blockStmt");
const auto *CtorCall = Result.Nodes.getNodeAs<CXXConstructExpr>("ctorCall");
// Do not propose fixes if the DeclStmt has multiple VarDecls or in macros
// since we cannot place them correctly.
bool IssueFix =
Result.Nodes.getNodeAs<DeclStmt>("declStmt")->isSingleDecl() &&
!NewVar->getLocation().isMacroID();
// A constructor that looks like T(const T& t, bool arg = false) counts as a
// copy only when it is called with default arguments for the arguments after
// the first.
for (unsigned int i = 1; i < CtorCall->getNumArgs(); ++i)
if (!CtorCall->getArg(i)->isDefaultArgument())
return;
if (OldVar == nullptr) {
handleCopyFromMethodReturn(*NewVar, *BlockStmt, IssueFix, ObjectArg,
*Result.Context);
} else {
handleCopyFromLocalVar(*NewVar, *OldVar, *BlockStmt, IssueFix,
*Result.Context);
}
}
void UnnecessaryCopyInitialization::handleCopyFromMethodReturn(
const VarDecl &Var, const Stmt &BlockStmt, bool IssueFix,
const VarDecl *ObjectArg, ASTContext &Context) {
bool IsConstQualified = Var.getType().isConstQualified();
if (!IsConstQualified && !isOnlyUsedAsConst(Var, BlockStmt, Context))
return;
if (ObjectArg != nullptr &&
!isOnlyUsedAsConst(*ObjectArg, BlockStmt, Context))
return;
auto Diagnostic =
diag(Var.getLocation(),
IsConstQualified ? "the const qualified variable %0 is "
"copy-constructed from a const reference; "
"consider making it a const reference"
: "the variable %0 is copy-constructed from a "
"const reference but is only used as const "
"reference; consider making it a const reference")
<< &Var;
if (IssueFix)
recordFixes(Var, Context, Diagnostic);
}
void UnnecessaryCopyInitialization::handleCopyFromLocalVar(
const VarDecl &NewVar, const VarDecl &OldVar, const Stmt &BlockStmt,
bool IssueFix, ASTContext &Context) {
if (!isOnlyUsedAsConst(NewVar, BlockStmt, Context) ||
!isOnlyUsedAsConst(OldVar, BlockStmt, Context))
return;
auto Diagnostic = diag(NewVar.getLocation(),
"local copy %0 of the variable %1 is never modified; "
"consider avoiding the copy")
<< &NewVar << &OldVar;
if (IssueFix)
recordFixes(NewVar, Context, Diagnostic);
}
void UnnecessaryCopyInitialization::storeOptions(
ClangTidyOptions::OptionMap &Opts) {
Options.store(Opts, "AllowedTypes",
utils::options::serializeStringList(AllowedTypes));
}
} // namespace performance
} // namespace tidy
} // namespace clang
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