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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 "RefCountedInsideLambdaChecker.h"
#include "CustomMatchers.h"
RefCountedMap RefCountedClasses;
void RefCountedInsideLambdaChecker::registerMatchers(MatchFinder *AstMatcher) {
// We want to reject any code which captures a pointer to an object of a
// refcounted type, and then lets that value escape. As a primitive analysis,
// we reject any occurances of the lambda as a template parameter to a class
// (which could allow it to escape), as well as any presence of such a lambda
// in a return value (either from lambdas, or in c++14, auto functions).
// We check these lambdas' capture lists for raw pointers to refcounted types.
AstMatcher->addMatcher(lambdaExpr().bind("lambdaExpr"), this);
void RefCountedInsideLambdaChecker::emitDiagnostics(SourceLocation Loc,
StringRef Name,
QualType Type) {
"Refcounted variable '%0' of type %1 cannot be captured by a lambda",
<< Name << Type;
diag(Loc, "Please consider using a smart pointer", DiagnosticIDs::Note);
static bool IsKnownLive(const VarDecl *Var) {
const Stmt *Init = Var->getInit();
if (!Init) {
return false;
if (auto *Call = dyn_cast<CallExpr>(Init)) {
const FunctionDecl *Callee = Call->getDirectCallee();
return Callee && Callee->getName() == "MOZ_KnownLive";
return false;
void RefCountedInsideLambdaChecker::check(
const MatchFinder::MatchResult &Result) {
static DenseSet<const CXXRecordDecl *> CheckedDecls;
const CXXRecordDecl *Lambda = Result.Nodes.getNodeAs<CXXRecordDecl>("decl");
if (const LambdaExpr *OuterLambda =
Result.Nodes.getNodeAs<LambdaExpr>("lambdaExpr")) {
const CXXMethodDecl *OpCall = OuterLambda->getCallOperator();
QualType ReturnTy = OpCall->getReturnType();
if (const CXXRecordDecl *Record = ReturnTy->getAsCXXRecordDecl()) {
Lambda = Record;
if (!Lambda || !Lambda->isLambda()) {
// Don't report errors on the same declarations more than once.
if (CheckedDecls.count(Lambda)) {
bool StrongRefToThisCaptured = false;
for (const LambdaCapture &Capture : Lambda->captures()) {
// Check if any of the captures are ByRef. If they are, we have nothing to
// report, as it's OK to capture raw pointers to refcounted objects so long
// as the Lambda doesn't escape the current scope, which is required by
// ByRef captures already.
if (Capture.getCaptureKind() == LCK_ByRef) {
// Check if this capture is byvalue, and captures a strong reference to
// this.
// XXX: Do we want to make sure that this type which we are capturing is a
// "Smart Pointer" somehow?
if (!StrongRefToThisCaptured && Capture.capturesVariable() &&
Capture.getCaptureKind() == LCK_ByCopy) {
const VarDecl *Var = dyn_cast<VarDecl>(Capture.getCapturedVar());
if (Var->hasInit()) {
const Stmt *Init = Var->getInit();
// Ignore single argument constructors, and trivial nodes.
while (true) {
auto NewInit = IgnoreTrivials(Init);
if (auto ConstructExpr = dyn_cast<CXXConstructExpr>(NewInit)) {
if (ConstructExpr->getNumArgs() == 1) {
NewInit = ConstructExpr->getArg(0);
if (Init == NewInit) {
Init = NewInit;
if (isa<CXXThisExpr>(Init)) {
StrongRefToThisCaptured = true;
// Now we can go through and produce errors for any captured variables or this
// pointers.
for (const LambdaCapture &Capture : Lambda->captures()) {
if (Capture.capturesVariable()) {
const VarDecl *Var = dyn_cast<VarDecl>(Capture.getCapturedVar());
QualType Pointee = Var->getType()->getPointeeType();
if (!Pointee.isNull() && isClassRefCounted(Pointee) &&
!IsKnownLive(Var)) {
emitDiagnostics(Capture.getLocation(), Var->getName(), Pointee);
// The situation with captures of `this` is more complex. All captures of
// `this` look the same-ish (they are LCK_This). We want to complain about
// captures of `this` where `this` is a refcounted type, and the capture is
// actually used in the body of the lambda (if the capture isn't used, then
// we don't care, because it's only being captured in order to give access
// to private methods).
// In addition, we don't complain about this, even if it is used, if it was
// captured implicitly when the LambdaCaptureDefault was LCD_ByRef, as that
// expresses the intent that the lambda won't leave the enclosing scope.
bool ImplicitByRefDefaultedCapture =
Capture.isImplicit() && Lambda->getLambdaCaptureDefault() == LCD_ByRef;
if (Capture.capturesThis() && !ImplicitByRefDefaultedCapture &&
!StrongRefToThisCaptured) {
ThisVisitor V(*this);
bool NotAborted = V.TraverseDecl(
const_cast<CXXMethodDecl *>(Lambda->getLambdaCallOperator()));
if (!NotAborted) {
bool RefCountedInsideLambdaChecker::ThisVisitor::VisitCXXThisExpr(
CXXThisExpr *This) {
QualType Pointee = This->getType()->getPointeeType();
if (!Pointee.isNull() && isClassRefCounted(Pointee)) {
Checker.emitDiagnostics(This->getBeginLoc(), "this", Pointee);
return false;
return true;