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[Clang] Only ignore special methods for unused private fields in BuildFieldReferenceExpr #116965

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Merged
merged 3 commits into from
Nov 26, 2024
Merged

[Clang] Only ignore special methods for unused private fields in BuildFieldReferenceExpr #116965

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[Clang] Only ignore special methods for unused private fields in Buil…
Maetveis Nov 20, 2024
acffeca
Add Release Notes and comments to test
Maetveis Nov 25, 2024
43cd9cd
Expand on test comment why the new test case is required
Maetveis Nov 26, 2024
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2 changes: 2 additions & 0 deletions clang/docs/ReleaseNotes.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -585,6 +585,8 @@ Improvements to Clang's diagnostics
- For an rvalue reference bound to a temporary struct with an integer member, Clang will detect constant integer overflow
in the initializer for the integer member (#GH46755).

- Fixed a false negative ``-Wunused-private-field`` diagnostic when a defaulted comparison operator is defined out of class (#GH116961).

Improvements to Clang's time-trace
----------------------------------

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12 changes: 10 additions & 2 deletions clang/lib/Sema/SemaExprMember.cpp
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Expand Up @@ -1874,8 +1874,16 @@ Sema::BuildFieldReferenceExpr(Expr *BaseExpr, bool IsArrow,
Context.getAttributedType(attr::NoDeref, MemberType, MemberType);
}

auto *CurMethod = dyn_cast<CXXMethodDecl>(CurContext);
if (!(CurMethod && CurMethod->isDefaulted()))
auto isDefaultedSpecialMember = [this](const DeclContext *Ctx) {
auto *Method = dyn_cast<CXXMethodDecl>(CurContext);
if (!Method || !Method->isDefaulted())
return false;

return getDefaultedFunctionKind(Method).isSpecialMember();
};

// Implicit special members should not mark fields as used.
if (!isDefaultedSpecialMember(CurContext))
UnusedPrivateFields.remove(Field);

ExprResult Base = PerformObjectMemberConversion(BaseExpr, SS.getScopeRep(),
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14 changes: 14 additions & 0 deletions clang/test/SemaCXX/warn-unused-private-field.cpp
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Expand Up @@ -20,6 +20,20 @@ class SpaceShipDefaultCompare {
int operator<=>(const SpaceShipDefaultCompare &) const = default;
};

class EqDefaultCompareOutOfClass {
int used; // no warning
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@erichkeane erichkeane Nov 25, 2024

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Please explain a touch better with 'no warning'? Something like, "Test to ensure that the defaulted operator results in this being seen as 'used' despite there not being code to do so."?

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@Maetveis Maetveis Nov 26, 2024 •
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Okay, sorry I wasn't sure what you were referring to, but I get now that from the change-set it is not obvious how / why the issue in #116961 is fixed, and why it is a special case not covered by the current testing. I expanded quite a bit on the comment, hopefully it did not become too verbose now.

bool operator==(const EqDefaultCompareOutOfClass &) const;
};

bool EqDefaultCompareOutOfClass::operator==(const EqDefaultCompareOutOfClass &) const = default;

class FriendEqDefaultCompareOutOfClass {
int used; // no warning
friend bool operator==(const FriendEqDefaultCompareOutOfClass &, const FriendEqDefaultCompareOutOfClass &);
};

bool operator==(const FriendEqDefaultCompareOutOfClass &, const FriendEqDefaultCompareOutOfClass &) = default;

#endif

class NotFullyDefined {
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