Ignore implicity casts for zero-as-null-pointer-constant warning

[erichkeane]

Summary

The repro in https://bugs.llvm.org/show_bug.cgi?id=34362
caused the left nullptr to be cast to a int* implicitly, which
resulted diagnosing this falsely.

[lebedev.ri]

test/SemaCXX/warn-zero-nullptr.cpp

29 ↗

(On Diff #120286)

Maybe wrap into a namespace PR34362 {}

[erichkeane]

Response to Roman's comment.

[aaron.ballman]

lib/Sema/Sema.cpp

441 ↗

(On Diff #120288)

Do we also want to ignore parens here as well with Expr::IgnoreParenImpCasts()?

[erichkeane]

lib/Sema/Sema.cpp

441 ↗

(On Diff #120288)

I don't see a reason why not! Patch incoming.

[erichkeane]

Lets ignore parens too!

[lebedev.ri]

lib/Sema/Sema.cpp

441 ↗

(On Diff #120288)

Probably needs a test too :)

[aaron.ballman]

LGTM!

[thakis]

Awesome, thanks much! Like lebedev.ri says, adding a test for the "Parens" part would be good.

[erichkeane]

They've got me presenting in the next meeting, but i'll add said test and commit after. Thanks for the reviews guys!

[aaron.ballman]

In D39301#906911, @thakis wrote:

Awesome, thanks much! Like lebedev.ri says, adding a test for the "Parens" part would be good.

I agree. I should have been more explicit with my LGTM, but I presumed you knew to add the tests already. ;-)

cfe/trunk/lib/Sema/Sema.cpp

if (!TypeNullability || *TypeNullability != NullabilityKind::NonNull)
     return;
 
   Diag(Loc, diag::warn_nullability_lost) << SrcType << DstType;
 }
 
 void Sema::diagnoseZeroToNullptrConversion(CastKind Kind, const Expr* E) {
   if (Kind != CK_NullToPointer && Kind != CK_NullToMemberPointer)
     return;
-  if (E->getType()->isNullPtrType())
+  if (E->IgnoreParenImpCasts()->getType()->isNullPtrType())
     return;
   // nullptr only exists from C++11 on, so don't warn on its absence earlier.
   if (!getLangOpts().CPlusPlus11)
     return;
 
   Diag(E->getLocStart(), diag::warn_zero_as_null_pointer_constant)
       << FixItHint::CreateReplacement(E->getSourceRange(), "nullptr");
 }

cfe/trunk/test/SemaCXX/warn-zero-nullptr.cpp

 
 void g() {
   f1(0); // expected-warning{{zero as null pointer constant}}
 }
 
 // Warn on these too. Matches gcc and arguably makes sense.
 void* pp = (decltype(nullptr))0; // expected-warning{{zero as null pointer constant}}
 void* pp2 = static_cast<decltype(nullptr)>(0); // expected-warning{{zero as null pointer constant}}
+
+// Shouldn't warn.
+namespace pr34362 {
+struct A { operator int*() { return nullptr; } };
+void func() { if (nullptr == A()) {} }
+void func2() { if ((nullptr) == A()) {} }
+}