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[clang] Fix possible nullptr deref in BuildCXXNestedNameSpecifier #166995

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Merged
merged 7 commits into from
Nov 10, 2025
Merged

[clang] Fix possible nullptr deref in BuildCXXNestedNameSpecifier #166995

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dbedc1c
[clang] Fix possible nullptr deref in BuildCXXNestedNameSpecifier
ilovepi Nov 7, 2025
be21d3d
Prefer early return to avoid excessive diff
ilovepi Nov 7, 2025
5796fc8
Add missing test case that wasn't uploaded
ilovepi Nov 7, 2025
1f6e1b6
Fix formatting
ilovepi Nov 7, 2025
b07be58
Merge branch 'main' into clang-deref-null
ilovepi Nov 7, 2025
7010a50
Merge branch 'main' into clang-deref-null
ilovepi Nov 7, 2025
710b262
Ensure correct diagnostic still gets used
ilovepi Nov 7, 2025
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2 changes: 2 additions & 0 deletions clang/lib/Sema/SemaCXXScopeSpec.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -780,6 +780,8 @@ bool Sema::BuildCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,

if (!Found.empty()) {
const auto *ND = Found.getAsSingle<NamedDecl>();
if(!ND)
return true;
if (::ExtendNestedNameSpecifier(*this, SS, ND, IdInfo.IdentifierLoc,
IdInfo.CCLoc)) {
const Type *T = SS.getScopeRep().getAsType();
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7 changes: 7 additions & 0 deletions clang/test/Sema/PR166843.cpp
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Original file line number Diff line number Diff line change
@@ -0,0 +1,7 @@
// RUN: %clang_cc1 -fsyntax-only %s -verify
namespace a {
template <class b>
void c() {
((::c::)); // expected-error {{expected unqualified-id}}
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@efriedma-quic efriedma-quic Nov 7, 2025

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This looks like we aren't actually diagnosing the error? I'd expect something like error: 'c' is not a class, namespace, or enumeration, which is what we generate in the non-template case.

What happens if you instead write the following?

  ((::c::x));

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@ilovepi ilovepi Nov 7, 2025

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This looks like we aren't actually diagnosing the error? I'd expect something like error: 'c' is not a class, namespace, or enumeration, which is what we generate in the non-template case.

Yeah, that was something I wasn't sure about.

What happens if you instead write the following?

  ((::c::x));

Looks like we report nothing, the way I've structured it. That version still causes the crash w/o the nullptr check, so let me update the check to make sure it works in the expected way.

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@ilovepi ilovepi Nov 7, 2025

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i've updated the early exit by duplicating the diagnostic. I didn't see an obvious way to avoid doing that. Happy to amend if this still isn't quite right.

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@ilovepi ilovepi Nov 10, 2025

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@efriedma-quic does the new version work the way you'd expect it to? I'd like to get this merged if it does.

}
}
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