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//===- DynamicTypePropagation.cpp ------------------------------*- C++ -*--===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file contains two checkers. One helps the static analyzer core to track
// types, the other does type inference on Obj-C generics and report type
// errors.
// Dynamic Type Propagation:
// This checker defines the rules for dynamic type gathering and propagation.
// Generics Checker for Objective-C:
// This checker tries to find type errors that the compiler is not able to catch
// due to the implicit conversions that were introduced for backward
// compatibility.
#include "clang/AST/ParentMap.h"
#include "clang/AST/RecursiveASTVisitor.h"
#include "clang/Basic/Builtins.h"
#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
#include "clang/StaticAnalyzer/Core/Checker.h"
#include "clang/StaticAnalyzer/Core/CheckerManager.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/DynamicType.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h"
using namespace clang;
using namespace ento;
// ProgramState trait - The type inflation is tracked by DynamicTypeMap. This is
// an auxiliary map that tracks more information about generic types, because in
// some cases the most derived type is not the most informative one about the
// type parameters. This types that are stored for each symbol in this map must
// be specialized.
// TODO: In some case the type stored in this map is exactly the same that is
// stored in DynamicTypeMap. We should no store duplicated information in those
// cases.
REGISTER_MAP_WITH_PROGRAMSTATE(MostSpecializedTypeArgsMap, SymbolRef,
const ObjCObjectPointerType *)
namespace {
class DynamicTypePropagation:
public Checker< check::PreCall,
check::PostObjCMessage > {
const ObjCObjectType *getObjectTypeForAllocAndNew(const ObjCMessageExpr *MsgE,
CheckerContext &C) const;
/// Return a better dynamic type if one can be derived from the cast.
const ObjCObjectPointerType *getBetterObjCType(const Expr *CastE,
CheckerContext &C) const;
ExplodedNode *dynamicTypePropagationOnCasts(const CastExpr *CE,
ProgramStateRef &State,
CheckerContext &C) const;
mutable std::unique_ptr<BugType> ObjCGenericsBugType;
void initBugType() const {
if (!ObjCGenericsBugType)
new BugType(this, "Generics", categories::CoreFoundationObjectiveC));
class GenericsBugVisitor : public BugReporterVisitor {
GenericsBugVisitor(SymbolRef S) : Sym(S) {}
void Profile(llvm::FoldingSetNodeID &ID) const override {
static int X = 0;
PathDiagnosticPieceRef VisitNode(const ExplodedNode *N,
BugReporterContext &BRC,
PathSensitiveBugReport &BR) override;
// The tracked symbol.
SymbolRef Sym;
void reportGenericsBug(const ObjCObjectPointerType *From,
const ObjCObjectPointerType *To, ExplodedNode *N,
SymbolRef Sym, CheckerContext &C,
const Stmt *ReportedNode = nullptr) const;
void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
void checkPostCall(const CallEvent &Call, CheckerContext &C) const;
void checkPostStmt(const CastExpr *CastE, CheckerContext &C) const;
void checkPostStmt(const CXXNewExpr *NewE, CheckerContext &C) const;
void checkDeadSymbols(SymbolReaper &SR, CheckerContext &C) const;
void checkPreObjCMessage(const ObjCMethodCall &M, CheckerContext &C) const;
void checkPostObjCMessage(const ObjCMethodCall &M, CheckerContext &C) const;
/// This value is set to true, when the Generics checker is turned on.
DefaultBool CheckGenerics;
} // end anonymous namespace
void DynamicTypePropagation::checkDeadSymbols(SymbolReaper &SR,
CheckerContext &C) const {
ProgramStateRef State = removeDeadTypes(C.getState(), SR);
MostSpecializedTypeArgsMapTy TyArgMap =
for (MostSpecializedTypeArgsMapTy::iterator I = TyArgMap.begin(),
E = TyArgMap.end();
I != E; ++I) {
if (SR.isDead(I->first)) {
State = State->remove<MostSpecializedTypeArgsMap>(I->first);
static void recordFixedType(const MemRegion *Region, const CXXMethodDecl *MD,
CheckerContext &C) {
ASTContext &Ctx = C.getASTContext();
QualType Ty = Ctx.getPointerType(Ctx.getRecordType(MD->getParent()));
ProgramStateRef State = C.getState();
State = setDynamicTypeInfo(State, Region, Ty, /*CanBeSubClassed=*/false);
void DynamicTypePropagation::checkPreCall(const CallEvent &Call,
CheckerContext &C) const {
if (const CXXConstructorCall *Ctor = dyn_cast<CXXConstructorCall>(&Call)) {
// C++11 [class.cdtor]p4: When a virtual function is called directly or
// indirectly from a constructor or from a destructor, including during
// the construction or destruction of the class's non-static data members,
// and the object to which the call applies is the object under
// construction or destruction, the function called is the final overrider
// in the constructor's or destructor's class and not one overriding it in
// a more-derived class.
switch (Ctor->getOriginExpr()->getConstructionKind()) {
case CXXConstructExpr::CK_Complete:
case CXXConstructExpr::CK_Delegating:
// No additional type info necessary.
case CXXConstructExpr::CK_NonVirtualBase:
case CXXConstructExpr::CK_VirtualBase:
if (const MemRegion *Target = Ctor->getCXXThisVal().getAsRegion())
recordFixedType(Target, Ctor->getDecl(), C);
if (const CXXDestructorCall *Dtor = dyn_cast<CXXDestructorCall>(&Call)) {
// C++11 [class.cdtor]p4 (see above)
if (!Dtor->isBaseDestructor())
const MemRegion *Target = Dtor->getCXXThisVal().getAsRegion();
if (!Target)
const Decl *D = Dtor->getDecl();
if (!D)
recordFixedType(Target, cast<CXXDestructorDecl>(D), C);
void DynamicTypePropagation::checkPostCall(const CallEvent &Call,
CheckerContext &C) const {
// We can obtain perfect type info for return values from some calls.
if (const ObjCMethodCall *Msg = dyn_cast<ObjCMethodCall>(&Call)) {
// Get the returned value if it's a region.
const MemRegion *RetReg = Call.getReturnValue().getAsRegion();
if (!RetReg)
ProgramStateRef State = C.getState();
const ObjCMethodDecl *D = Msg->getDecl();
if (D && D->hasRelatedResultType()) {
switch (Msg->getMethodFamily()) {
// We assume that the type of the object returned by alloc and new are the
// pointer to the object of the class specified in the receiver of the
// message.
case OMF_alloc:
case OMF_new: {
// Get the type of object that will get created.
const ObjCMessageExpr *MsgE = Msg->getOriginExpr();
const ObjCObjectType *ObjTy = getObjectTypeForAllocAndNew(MsgE, C);
if (!ObjTy)
QualType DynResTy =
C.getASTContext().getObjCObjectPointerType(QualType(ObjTy, 0));
C.addTransition(setDynamicTypeInfo(State, RetReg, DynResTy, false));
case OMF_init: {
// Assume, the result of the init method has the same dynamic type as
// the receiver and propagate the dynamic type info.
const MemRegion *RecReg = Msg->getReceiverSVal().getAsRegion();
if (!RecReg)
DynamicTypeInfo RecDynType = getDynamicTypeInfo(State, RecReg);
C.addTransition(setDynamicTypeInfo(State, RetReg, RecDynType));
if (const CXXConstructorCall *Ctor = dyn_cast<CXXConstructorCall>(&Call)) {
// We may need to undo the effects of our pre-call check.
switch (Ctor->getOriginExpr()->getConstructionKind()) {
case CXXConstructExpr::CK_Complete:
case CXXConstructExpr::CK_Delegating:
// No additional work necessary.
// Note: This will leave behind the actual type of the object for
// complete constructors, but arguably that's a good thing, since it
// means the dynamic type info will be correct even for objects
// constructed with operator new.
case CXXConstructExpr::CK_NonVirtualBase:
case CXXConstructExpr::CK_VirtualBase:
if (const MemRegion *Target = Ctor->getCXXThisVal().getAsRegion()) {
// We just finished a base constructor. Now we can use the subclass's
// type when resolving virtual calls.
const LocationContext *LCtx = C.getLocationContext();
// FIXME: In C++17 classes with non-virtual bases may be treated as
// aggregates, and in such case no top-frame constructor will be called.
// Figure out if we need to do anything in this case.
// FIXME: Instead of relying on the ParentMap, we should have the
// trigger-statement (InitListExpr in this case) available in this
// callback, ideally as part of CallEvent.
if (dyn_cast_or_null<InitListExpr>(
recordFixedType(Target, cast<CXXConstructorDecl>(LCtx->getDecl()), C);
/// TODO: Handle explicit casts.
/// Handle C++ casts.
/// Precondition: the cast is between ObjCObjectPointers.
ExplodedNode *DynamicTypePropagation::dynamicTypePropagationOnCasts(
const CastExpr *CE, ProgramStateRef &State, CheckerContext &C) const {
// We only track type info for regions.
const MemRegion *ToR = C.getSVal(CE).getAsRegion();
if (!ToR)
return C.getPredecessor();
if (isa<ExplicitCastExpr>(CE))
return C.getPredecessor();
if (const Type *NewTy = getBetterObjCType(CE, C)) {
State = setDynamicTypeInfo(State, ToR, QualType(NewTy, 0));
return C.addTransition(State);
return C.getPredecessor();
void DynamicTypePropagation::checkPostStmt(const CXXNewExpr *NewE,
CheckerContext &C) const {
if (NewE->isArray())
// We only track dynamic type info for regions.
const MemRegion *MR = C.getSVal(NewE).getAsRegion();
if (!MR)
C.addTransition(setDynamicTypeInfo(C.getState(), MR, NewE->getType(),
const ObjCObjectType *
DynamicTypePropagation::getObjectTypeForAllocAndNew(const ObjCMessageExpr *MsgE,
CheckerContext &C) const {
if (MsgE->getReceiverKind() == ObjCMessageExpr::Class) {
if (const ObjCObjectType *ObjTy
= MsgE->getClassReceiver()->getAs<ObjCObjectType>())
return ObjTy;
if (MsgE->getReceiverKind() == ObjCMessageExpr::SuperClass) {
if (const ObjCObjectType *ObjTy
= MsgE->getSuperType()->getAs<ObjCObjectType>())
return ObjTy;
const Expr *RecE = MsgE->getInstanceReceiver();
if (!RecE)
return nullptr;
RecE= RecE->IgnoreParenImpCasts();
if (const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(RecE)) {
const StackFrameContext *SFCtx = C.getStackFrame();
// Are we calling [self alloc]? If this is self, get the type of the
// enclosing ObjC class.
if (DRE->getDecl() == SFCtx->getSelfDecl()) {
if (const ObjCMethodDecl *MD = dyn_cast<ObjCMethodDecl>(SFCtx->getDecl()))
if (const ObjCObjectType *ObjTy =
return ObjTy;
return nullptr;
// Return a better dynamic type if one can be derived from the cast.
// Compare the current dynamic type of the region and the new type to which we
// are casting. If the new type is lower in the inheritance hierarchy, pick it.
const ObjCObjectPointerType *
DynamicTypePropagation::getBetterObjCType(const Expr *CastE,
CheckerContext &C) const {
const MemRegion *ToR = C.getSVal(CastE).getAsRegion();
// Get the old and new types.
const ObjCObjectPointerType *NewTy =
if (!NewTy)
return nullptr;
QualType OldDTy = getDynamicTypeInfo(C.getState(), ToR).getType();
if (OldDTy.isNull()) {
return NewTy;
const ObjCObjectPointerType *OldTy =
if (!OldTy)
return nullptr;
// Id the old type is 'id', the new one is more precise.
if (OldTy->isObjCIdType() && !NewTy->isObjCIdType())
return NewTy;
// Return new if it's a subclass of old.
const ObjCInterfaceDecl *ToI = NewTy->getInterfaceDecl();
const ObjCInterfaceDecl *FromI = OldTy->getInterfaceDecl();
if (ToI && FromI && FromI->isSuperClassOf(ToI))
return NewTy;
return nullptr;
static const ObjCObjectPointerType *getMostInformativeDerivedClassImpl(
const ObjCObjectPointerType *From, const ObjCObjectPointerType *To,
const ObjCObjectPointerType *MostInformativeCandidate, ASTContext &C) {
// Checking if from and to are the same classes modulo specialization.
if (From->getInterfaceDecl()->getCanonicalDecl() ==
To->getInterfaceDecl()->getCanonicalDecl()) {
if (To->isSpecialized()) {
return MostInformativeCandidate;
return From;
if (To->getObjectType()->getSuperClassType().isNull()) {
// If To has no super class and From and To aren't the same then
// To was not actually a descendent of From. In this case the best we can
// do is 'From'.
return From;
const auto *SuperOfTo =
QualType SuperPtrOfToQual =
C.getObjCObjectPointerType(QualType(SuperOfTo, 0));
const auto *SuperPtrOfTo = SuperPtrOfToQual->castAs<ObjCObjectPointerType>();
if (To->isUnspecialized())
return getMostInformativeDerivedClassImpl(From, SuperPtrOfTo, SuperPtrOfTo,
return getMostInformativeDerivedClassImpl(From, SuperPtrOfTo,
MostInformativeCandidate, C);
/// A downcast may loose specialization information. E. g.:
/// MutableMap<T, U> : Map
/// The downcast to MutableMap looses the information about the types of the
/// Map (due to the type parameters are not being forwarded to Map), and in
/// general there is no way to recover that information from the
/// declaration. In order to have to most information, lets find the most
/// derived type that has all the type parameters forwarded.
/// Get the a subclass of \p From (which has a lower bound \p To) that do not
/// loose information about type parameters. \p To has to be a subclass of
/// \p From. From has to be specialized.
static const ObjCObjectPointerType *
getMostInformativeDerivedClass(const ObjCObjectPointerType *From,
const ObjCObjectPointerType *To, ASTContext &C) {
return getMostInformativeDerivedClassImpl(From, To, To, C);
/// Inputs:
/// \param StaticLowerBound Static lower bound for a symbol. The dynamic lower
/// bound might be the subclass of this type.
/// \param StaticUpperBound A static upper bound for a symbol.
/// \p StaticLowerBound expected to be the subclass of \p StaticUpperBound.
/// \param Current The type that was inferred for a symbol in a previous
/// context. Might be null when this is the first time that inference happens.
/// Precondition:
/// \p StaticLowerBound or \p StaticUpperBound is specialized. If \p Current
/// is not null, it is specialized.
/// Possible cases:
/// (1) The \p Current is null and \p StaticLowerBound <: \p StaticUpperBound
/// (2) \p StaticLowerBound <: \p Current <: \p StaticUpperBound
/// (3) \p Current <: \p StaticLowerBound <: \p StaticUpperBound
/// (4) \p StaticLowerBound <: \p StaticUpperBound <: \p Current
/// Effect:
/// Use getMostInformativeDerivedClass with the upper and lower bound of the
/// set {\p StaticLowerBound, \p Current, \p StaticUpperBound}. The computed
/// lower bound must be specialized. If the result differs from \p Current or
/// \p Current is null, store the result.
static bool
storeWhenMoreInformative(ProgramStateRef &State, SymbolRef Sym,
const ObjCObjectPointerType *const *Current,
const ObjCObjectPointerType *StaticLowerBound,
const ObjCObjectPointerType *StaticUpperBound,
ASTContext &C) {
// TODO: The above 4 cases are not exhaustive. In particular, it is possible
// for Current to be incomparable with StaticLowerBound, StaticUpperBound,
// or both.
// For example, suppose Foo<T> and Bar<T> are unrelated types.
// Foo<T> *f = ...
// Bar<T> *b = ...
// id t1 = b;
// f = t1;
// id t2 = f; // StaticLowerBound is Foo<T>, Current is Bar<T>
// We should either constrain the callers of this function so that the stated
// preconditions hold (and assert it) or rewrite the function to expicitly
// handle the additional cases.
// Precondition
assert(StaticUpperBound->isSpecialized() ||
assert(!Current || (*Current)->isSpecialized());
// Case (1)
if (!Current) {
if (StaticUpperBound->isUnspecialized()) {
State = State->set<MostSpecializedTypeArgsMap>(Sym, StaticLowerBound);
return true;
// Upper bound is specialized.
const ObjCObjectPointerType *WithMostInfo =
getMostInformativeDerivedClass(StaticUpperBound, StaticLowerBound, C);
State = State->set<MostSpecializedTypeArgsMap>(Sym, WithMostInfo);
return true;
// Case (3)
if (C.canAssignObjCInterfaces(StaticLowerBound, *Current)) {
return false;
// Case (4)
if (C.canAssignObjCInterfaces(*Current, StaticUpperBound)) {
// The type arguments might not be forwarded at any point of inheritance.
const ObjCObjectPointerType *WithMostInfo =
getMostInformativeDerivedClass(*Current, StaticUpperBound, C);
WithMostInfo =
getMostInformativeDerivedClass(WithMostInfo, StaticLowerBound, C);
if (WithMostInfo == *Current)
return false;
State = State->set<MostSpecializedTypeArgsMap>(Sym, WithMostInfo);
return true;
// Case (2)
const ObjCObjectPointerType *WithMostInfo =
getMostInformativeDerivedClass(*Current, StaticLowerBound, C);
if (WithMostInfo != *Current) {
State = State->set<MostSpecializedTypeArgsMap>(Sym, WithMostInfo);
return true;
return false;
/// Type inference based on static type information that is available for the
/// cast and the tracked type information for the given symbol. When the tracked
/// symbol and the destination type of the cast are unrelated, report an error.
void DynamicTypePropagation::checkPostStmt(const CastExpr *CE,
CheckerContext &C) const {
if (CE->getCastKind() != CK_BitCast)
QualType OriginType = CE->getSubExpr()->getType();
QualType DestType = CE->getType();
const auto *OrigObjectPtrType = OriginType->getAs<ObjCObjectPointerType>();
const auto *DestObjectPtrType = DestType->getAs<ObjCObjectPointerType>();
if (!OrigObjectPtrType || !DestObjectPtrType)
ProgramStateRef State = C.getState();
ExplodedNode *AfterTypeProp = dynamicTypePropagationOnCasts(CE, State, C);
ASTContext &ASTCtxt = C.getASTContext();
// This checker detects the subtyping relationships using the assignment
// rules. In order to be able to do this the kindofness must be stripped
// first. The checker treats every type as kindof type anyways: when the
// tracked type is the subtype of the static type it tries to look up the
// methods in the tracked type first.
OrigObjectPtrType = OrigObjectPtrType->stripObjCKindOfTypeAndQuals(ASTCtxt);
DestObjectPtrType = DestObjectPtrType->stripObjCKindOfTypeAndQuals(ASTCtxt);
if (OrigObjectPtrType->isUnspecialized() &&
SymbolRef Sym = C.getSVal(CE).getAsSymbol();
if (!Sym)
const ObjCObjectPointerType *const *TrackedType =
if (isa<ExplicitCastExpr>(CE)) {
// Treat explicit casts as an indication from the programmer that the
// Objective-C type system is not rich enough to express the needed
// invariant. In such cases, forget any existing information inferred
// about the type arguments. We don't assume the casted-to specialized
// type here because the invariant the programmer specifies in the cast
// may only hold at this particular program point and not later ones.
// We don't want a suppressing cast to require a cascade of casts down the
// line.
if (TrackedType) {
State = State->remove<MostSpecializedTypeArgsMap>(Sym);
C.addTransition(State, AfterTypeProp);
// Check which assignments are legal.
bool OrigToDest =
ASTCtxt.canAssignObjCInterfaces(DestObjectPtrType, OrigObjectPtrType);
bool DestToOrig =
ASTCtxt.canAssignObjCInterfaces(OrigObjectPtrType, DestObjectPtrType);
// The tracked type should be the sub or super class of the static destination
// type. When an (implicit) upcast or a downcast happens according to static
// types, and there is no subtyping relationship between the tracked and the
// static destination types, it indicates an error.
if (TrackedType &&
!ASTCtxt.canAssignObjCInterfaces(DestObjectPtrType, *TrackedType) &&
!ASTCtxt.canAssignObjCInterfaces(*TrackedType, DestObjectPtrType)) {
static CheckerProgramPointTag IllegalConv(this, "IllegalConversion");
ExplodedNode *N = C.addTransition(State, AfterTypeProp, &IllegalConv);
reportGenericsBug(*TrackedType, DestObjectPtrType, N, Sym, C);
// Handle downcasts and upcasts.
const ObjCObjectPointerType *LowerBound = DestObjectPtrType;
const ObjCObjectPointerType *UpperBound = OrigObjectPtrType;
if (OrigToDest && !DestToOrig)
std::swap(LowerBound, UpperBound);
// The id type is not a real bound. Eliminate it.
LowerBound = LowerBound->isObjCIdType() ? UpperBound : LowerBound;
UpperBound = UpperBound->isObjCIdType() ? LowerBound : UpperBound;
if (storeWhenMoreInformative(State, Sym, TrackedType, LowerBound, UpperBound,
ASTCtxt)) {
C.addTransition(State, AfterTypeProp);
static const Expr *stripCastsAndSugar(const Expr *E) {
E = E->IgnoreParenImpCasts();
if (const PseudoObjectExpr *POE = dyn_cast<PseudoObjectExpr>(E))
E = POE->getSyntacticForm()->IgnoreParenImpCasts();
if (const OpaqueValueExpr *OVE = dyn_cast<OpaqueValueExpr>(E))
E = OVE->getSourceExpr()->IgnoreParenImpCasts();
return E;
static bool isObjCTypeParamDependent(QualType Type) {
// It is illegal to typedef parameterized types inside an interface. Therefore
// an Objective-C type can only be dependent on a type parameter when the type
// parameter structurally present in the type itself.
class IsObjCTypeParamDependentTypeVisitor
: public RecursiveASTVisitor<IsObjCTypeParamDependentTypeVisitor> {
IsObjCTypeParamDependentTypeVisitor() : Result(false) {}
bool VisitObjCTypeParamType(const ObjCTypeParamType *Type) {
if (isa<ObjCTypeParamDecl>(Type->getDecl())) {
Result = true;
return false;
return true;
bool Result;
IsObjCTypeParamDependentTypeVisitor Visitor;
return Visitor.Result;
/// A method might not be available in the interface indicated by the static
/// type. However it might be available in the tracked type. In order to
/// properly substitute the type parameters we need the declaration context of
/// the method. The more specialized the enclosing class of the method is, the
/// more likely that the parameter substitution will be successful.
static const ObjCMethodDecl *
findMethodDecl(const ObjCMessageExpr *MessageExpr,
const ObjCObjectPointerType *TrackedType, ASTContext &ASTCtxt) {
const ObjCMethodDecl *Method = nullptr;
QualType ReceiverType = MessageExpr->getReceiverType();
const auto *ReceiverObjectPtrType =
// Do this "devirtualization" on instance and class methods only. Trust the
// static type on super and super class calls.
if (MessageExpr->getReceiverKind() == ObjCMessageExpr::Instance ||
MessageExpr->getReceiverKind() == ObjCMessageExpr::Class) {
// When the receiver type is id, Class, or some super class of the tracked
// type, look up the method in the tracked type, not in the receiver type.
// This way we preserve more information.
if (ReceiverType->isObjCIdType() || ReceiverType->isObjCClassType() ||
ASTCtxt.canAssignObjCInterfaces(ReceiverObjectPtrType, TrackedType)) {
const ObjCInterfaceDecl *InterfaceDecl = TrackedType->getInterfaceDecl();
// The method might not be found.
Selector Sel = MessageExpr->getSelector();
Method = InterfaceDecl->lookupInstanceMethod(Sel);
if (!Method)
Method = InterfaceDecl->lookupClassMethod(Sel);
// Fallback to statick method lookup when the one based on the tracked type
// failed.
return Method ? Method : MessageExpr->getMethodDecl();
/// Get the returned ObjCObjectPointerType by a method based on the tracked type
/// information, or null pointer when the returned type is not an
/// ObjCObjectPointerType.
static QualType getReturnTypeForMethod(
const ObjCMethodDecl *Method, ArrayRef<QualType> TypeArgs,
const ObjCObjectPointerType *SelfType, ASTContext &C) {
QualType StaticResultType = Method->getReturnType();
// Is the return type declared as instance type?
if (StaticResultType == C.getObjCInstanceType())
return QualType(SelfType, 0);
// Check whether the result type depends on a type parameter.
if (!isObjCTypeParamDependent(StaticResultType))
return QualType();
QualType ResultType = StaticResultType.substObjCTypeArgs(
C, TypeArgs, ObjCSubstitutionContext::Result);
return ResultType;
/// When the receiver has a tracked type, use that type to validate the
/// argumments of the message expression and the return value.
void DynamicTypePropagation::checkPreObjCMessage(const ObjCMethodCall &M,
CheckerContext &C) const {
ProgramStateRef State = C.getState();
SymbolRef Sym = M.getReceiverSVal().getAsSymbol();
if (!Sym)
const ObjCObjectPointerType *const *TrackedType =
if (!TrackedType)
// Get the type arguments from tracked type and substitute type arguments
// before do the semantic check.
ASTContext &ASTCtxt = C.getASTContext();
const ObjCMessageExpr *MessageExpr = M.getOriginExpr();
const ObjCMethodDecl *Method =
findMethodDecl(MessageExpr, *TrackedType, ASTCtxt);
// It is possible to call non-existent methods in Obj-C.
if (!Method)
// If the method is declared on a class that has a non-invariant
// type parameter, don't warn about parameter mismatches after performing
// substitution. This prevents warning when the programmer has purposely
// casted the receiver to a super type or unspecialized type but the analyzer
// has a more precise tracked type than the programmer intends at the call
// site.
// For example, consider NSArray (which has a covariant type parameter)
// and NSMutableArray (a subclass of NSArray where the type parameter is
// invariant):
// NSMutableArray *a = [[NSMutableArray<NSString *> alloc] init;
// [a containsObject:number]; // Safe: -containsObject is defined on NSArray.
// NSArray<NSObject *> *other = [a arrayByAddingObject:number] // Safe
// [a addObject:number] // Unsafe: -addObject: is defined on NSMutableArray
const ObjCInterfaceDecl *Interface = Method->getClassInterface();
if (!Interface)
ObjCTypeParamList *TypeParams = Interface->getTypeParamList();
if (!TypeParams)
for (ObjCTypeParamDecl *TypeParam : *TypeParams) {
if (TypeParam->getVariance() != ObjCTypeParamVariance::Invariant)
Optional<ArrayRef<QualType>> TypeArgs =
// This case might happen when there is an unspecialized override of a
// specialized method.
if (!TypeArgs)
for (unsigned i = 0; i < Method->param_size(); i++) {
const Expr *Arg = MessageExpr->getArg(i);
const ParmVarDecl *Param = Method->parameters()[i];
QualType OrigParamType = Param->getType();
if (!isObjCTypeParamDependent(OrigParamType))
QualType ParamType = OrigParamType.substObjCTypeArgs(
ASTCtxt, *TypeArgs, ObjCSubstitutionContext::Parameter);
// Check if it can be assigned
const auto *ParamObjectPtrType = ParamType->getAs<ObjCObjectPointerType>();
const auto *ArgObjectPtrType =
if (!ParamObjectPtrType || !ArgObjectPtrType)
// Check if we have more concrete tracked type that is not a super type of
// the static argument type.
SVal ArgSVal = M.getArgSVal(i);
SymbolRef ArgSym = ArgSVal.getAsSymbol();
if (ArgSym) {
const ObjCObjectPointerType *const *TrackedArgType =
if (TrackedArgType &&
ASTCtxt.canAssignObjCInterfaces(ArgObjectPtrType, *TrackedArgType)) {
ArgObjectPtrType = *TrackedArgType;
// Warn when argument is incompatible with the parameter.
if (!ASTCtxt.canAssignObjCInterfaces(ParamObjectPtrType,
ArgObjectPtrType)) {
static CheckerProgramPointTag Tag(this, "ArgTypeMismatch");
ExplodedNode *N = C.addTransition(State, &Tag);
reportGenericsBug(ArgObjectPtrType, ParamObjectPtrType, N, Sym, C, Arg);
/// This callback is used to infer the types for Class variables. This info is
/// used later to validate messages that sent to classes. Class variables are
/// initialized with by invoking the 'class' method on a class.
/// This method is also used to infer the type information for the return
/// types.
// TODO: right now it only tracks generic types. Extend this to track every
// type in the DynamicTypeMap and diagnose type errors!
void DynamicTypePropagation::checkPostObjCMessage(const ObjCMethodCall &M,
CheckerContext &C) const {
const ObjCMessageExpr *MessageExpr = M.getOriginExpr();
SymbolRef RetSym = M.getReturnValue().getAsSymbol();
if (!RetSym)
Selector Sel = MessageExpr->getSelector();
ProgramStateRef State = C.getState();
// Inference for class variables.
// We are only interested in cases where the class method is invoked on a
// class. This method is provided by the runtime and available on all classes.
if (MessageExpr->getReceiverKind() == ObjCMessageExpr::Class &&
Sel.getAsString() == "class") {
QualType ReceiverType = MessageExpr->getClassReceiver();
const auto *ReceiverClassType = ReceiverType->castAs<ObjCObjectType>();
if (!ReceiverClassType->isSpecialized())
QualType ReceiverClassPointerType =
QualType(ReceiverClassType, 0));
const auto *InferredType =
State = State->set<MostSpecializedTypeArgsMap>(RetSym, InferredType);
// Tracking for return types.
SymbolRef RecSym = M.getReceiverSVal().getAsSymbol();
if (!RecSym)
const ObjCObjectPointerType *const *TrackedType =
if (!TrackedType)
ASTContext &ASTCtxt = C.getASTContext();
const ObjCMethodDecl *Method =
findMethodDecl(MessageExpr, *TrackedType, ASTCtxt);
if (!Method)
Optional<ArrayRef<QualType>> TypeArgs =
if (!TypeArgs)
QualType ResultType =
getReturnTypeForMethod(Method, *TypeArgs, *TrackedType, ASTCtxt);
// The static type is the same as the deduced type.
if (ResultType.isNull())
const MemRegion *RetRegion = M.getReturnValue().getAsRegion();
ExplodedNode *Pred = C.getPredecessor();
// When there is an entry available for the return symbol in DynamicTypeMap,
// the call was inlined, and the information in the DynamicTypeMap is should
// be precise.
if (RetRegion && !getRawDynamicTypeInfo(State, RetRegion)) {
// TODO: we have duplicated information in DynamicTypeMap and
// MostSpecializedTypeArgsMap. We should only store anything in the later if
// the stored data differs from the one stored in the former.
State = setDynamicTypeInfo(State, RetRegion, ResultType,
Pred = C.addTransition(State);
const auto *ResultPtrType = ResultType->getAs<ObjCObjectPointerType>();
if (!ResultPtrType || ResultPtrType->isUnspecialized())
// When the result is a specialized type and it is not tracked yet, track it
// for the result symbol.
if (!State->get<MostSpecializedTypeArgsMap>(RetSym)) {
State = State->set<MostSpecializedTypeArgsMap>(RetSym, ResultPtrType);
C.addTransition(State, Pred);
void DynamicTypePropagation::reportGenericsBug(
const ObjCObjectPointerType *From, const ObjCObjectPointerType *To,
ExplodedNode *N, SymbolRef Sym, CheckerContext &C,
const Stmt *ReportedNode) const {
if (!CheckGenerics)
SmallString<192> Buf;
llvm::raw_svector_ostream OS(Buf);
OS << "Conversion from value of type '";
QualType::print(From, Qualifiers(), OS, C.getLangOpts(), llvm::Twine());
OS << "' to incompatible type '";
QualType::print(To, Qualifiers(), OS, C.getLangOpts(), llvm::Twine());
OS << "'";
auto R = std::make_unique<PathSensitiveBugReport>(*ObjCGenericsBugType,
OS.str(), N);
if (ReportedNode)
PathDiagnosticPieceRef DynamicTypePropagation::GenericsBugVisitor::VisitNode(
const ExplodedNode *N, BugReporterContext &BRC,
PathSensitiveBugReport &BR) {
ProgramStateRef state = N->getState();
ProgramStateRef statePrev = N->getFirstPred()->getState();
const ObjCObjectPointerType *const *TrackedType =
const ObjCObjectPointerType *const *TrackedTypePrev =
if (!TrackedType)
return nullptr;
if (TrackedTypePrev && *TrackedTypePrev == *TrackedType)
return nullptr;
// Retrieve the associated statement.
const Stmt *S = N->getStmtForDiagnostics();
if (!S)
return nullptr;
const LangOptions &LangOpts = BRC.getASTContext().getLangOpts();
SmallString<256> Buf;
llvm::raw_svector_ostream OS(Buf);
OS << "Type '";
QualType::print(*TrackedType, Qualifiers(), OS, LangOpts, llvm::Twine());
OS << "' is inferred from ";
if (const auto *ExplicitCast = dyn_cast<ExplicitCastExpr>(S)) {
OS << "explicit cast (from '";
Qualifiers(), OS, LangOpts, llvm::Twine());
OS << "' to '";
QualType::print(ExplicitCast->getType().getTypePtr(), Qualifiers(), OS,
LangOpts, llvm::Twine());
OS << "')";
} else if (const auto *ImplicitCast = dyn_cast<ImplicitCastExpr>(S)) {
OS << "implicit cast (from '";
Qualifiers(), OS, LangOpts, llvm::Twine());
OS << "' to '";
QualType::print(ImplicitCast->getType().getTypePtr(), Qualifiers(), OS,
LangOpts, llvm::Twine());
OS << "')";
} else {
OS << "this context";
// Generate the extra diagnostic.
PathDiagnosticLocation Pos(S, BRC.getSourceManager(),
return std::make_shared<PathDiagnosticEventPiece>(Pos, OS.str(), true);
/// Register checkers.
void ento::registerObjCGenericsChecker(CheckerManager &mgr) {
DynamicTypePropagation *checker = mgr.getChecker<DynamicTypePropagation>();
checker->CheckGenerics = true;
bool ento::shouldRegisterObjCGenericsChecker(const LangOptions &LO) {
return true;
void ento::registerDynamicTypePropagation(CheckerManager &mgr) {
bool ento::shouldRegisterDynamicTypePropagation(const LangOptions &LO) {
return true;