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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
#include "KungFuDeathGripChecker.h"
#include "CustomMatchers.h"
void KungFuDeathGripChecker::registerMatchers(MatchFinder *AstMatcher) {
AstMatcher->addMatcher(varDecl(allOf(hasType(isRefPtr()), hasLocalStorage(),
void KungFuDeathGripChecker::check(const MatchFinder::MatchResult &Result) {
const char *Error = "Unused \"kungFuDeathGrip\" %0 objects constructed from "
"%1 are prohibited";
const char *Note = "Please switch all accesses to this %0 to go through "
"'%1', or explicitly pass '%1' to `mozilla::Unused`";
const VarDecl *D = Result.Nodes.getNodeAs<VarDecl>("decl");
if (D->isReferenced()) {
// Not interested in parameters.
if (isa<ImplicitParamDecl>(D) || isa<ParmVarDecl>(D)) {
const Expr *E = IgnoreTrivials(D->getInit());
const CXXConstructExpr *CE = dyn_cast<CXXConstructExpr>(E);
if (CE && CE->getNumArgs() == 0) {
// We don't report an error when we construct and don't use a nsCOMPtr /
// nsRefPtr with no arguments. We don't report it because the error is not
// related to the current check. In the future it may be reported through a
// more generic mechanism.
// We don't want to look at the single argument conversion constructors
// which are inbetween the declaration and the actual object which we are
// assigning into the nsCOMPtr/RefPtr. To do this, we repeatedly
// IgnoreTrivials, then look at the expression. If it is one of these
// conversion constructors, we ignore it and continue to dig.
while ((CE = dyn_cast<CXXConstructExpr>(E)) && CE->getNumArgs() == 1) {
E = IgnoreTrivials(CE->getArg(0));
// If the argument expression is an xvalue, we are not taking a copy of
// anything.
if (E->isXValue()) {
// It is possible that the QualType doesn't point to a type yet so we are
// not interested.
if (E->getType().isNull()) {
// We allow taking a kungFuDeathGrip of `this` because it cannot change
// beneath us, so calling directly through `this` is OK. This is the same
// for local variable declarations.
// We also don't complain about unused RefPtrs which are constructed from
// the return value of a new expression, as these are required in order to
// immediately destroy the value created (which was presumably created for
// its side effects), and are not used as a death grip.
if (isa<CXXThisExpr>(E) || isa<DeclRefExpr>(E) || isa<CXXNewExpr>(E)) {
// These types are assigned into nsCOMPtr and RefPtr for their side effects,
// and not as a kungFuDeathGrip. We don't want to consider RefPtr and nsCOMPtr
// types which are initialized with these types as errors.
const TagDecl *TD = E->getType()->getAsTagDecl();
if (TD && TD->getIdentifier()) {
static const char *IgnoreTypes[] = {
for (uint32_t i = 0; i < sizeof(IgnoreTypes) / sizeof(IgnoreTypes[0]);
++i) {
if (TD->getName() == IgnoreTypes[i]) {
// Report the error
const char *ErrThing;
const char *NoteThing;
if (isa<MemberExpr>(E)) {
ErrThing = "members";
NoteThing = "member";
} else {
ErrThing = "temporary values";
NoteThing = "value";
// We cannot provide the note if we don't have an initializer
diag(D->getBeginLoc(), Error, DiagnosticIDs::Error)
<< D->getType() << ErrThing;
diag(E->getBeginLoc(), Note, DiagnosticIDs::Note)
<< NoteThing << getNameChecked(D);