[Clang] handle [[warn_unused]] attribute for unused private fields #120734
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@llvm/pr-subscribers-clang Author: Oleksandr T. (a-tarasyuk) ChangesFixes #62472 Full diff: https://github.com/llvm/llvm-project/pull/120734.diff 3 Files Affected:
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index a85ef60b7b58ba..c1d3596140721e 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -707,6 +707,7 @@ Improvements to Clang's diagnostics
}
- Fix -Wdangling false positives on conditional operators (#120206).
+- Clang now diagnoses unused private fields with the ``[[warn_unused]]`` attribute (#GH62472).
Improvements to Clang's time-trace
----------------------------------
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index c5a72cf812ebc9..760ed06fc1b858 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -3307,6 +3307,29 @@ void Sema::CheckShadowInheritedFields(const SourceLocation &Loc,
}
}
+template <typename AttrType>
+inline static bool HasAttribute(const QualType &T) {
+ if (const TagDecl *TD = T->getAsTagDecl())
+ return TD->hasAttr<AttrType>();
+ if (const TypedefType *TDT = T->getAs<TypedefType>())
+ return TDT->getDecl()->hasAttr<AttrType>();
+ return false;
+}
+
+inline static bool IsUnusedPrivateField(FieldDecl *FD) {
+ if (FD->getAccess() == AS_private && FD->getDeclName()) {
+ QualType FieldType = FD->getType();
+ if (HasAttribute<WarnUnusedAttr>(FieldType))
+ return true;
+
+ return !FD->isImplicit() && !FD->hasAttr<UnusedAttr>() &&
+ !FD->getParent()->isDependentContext() &&
+ !HasAttribute<UnusedAttr>(FieldType) &&
+ !InitializationHasSideEffects(*FD);
+ }
+ return false;
+}
+
NamedDecl *
Sema::ActOnCXXMemberDeclarator(Scope *S, AccessSpecifier AS, Declarator &D,
MultiTemplateParamsArg TemplateParameterLists,
@@ -3589,25 +3612,11 @@ Sema::ActOnCXXMemberDeclarator(Scope *S, AccessSpecifier AS, Declarator &D,
FieldDecl *FD = cast<FieldDecl>(Member);
FieldCollector->Add(FD);
- if (!Diags.isIgnored(diag::warn_unused_private_field, FD->getLocation())) {
+ if (!Diags.isIgnored(diag::warn_unused_private_field, FD->getLocation()) &&
+ IsUnusedPrivateField(FD)) {
// Remember all explicit private FieldDecls that have a name, no side
// effects and are not part of a dependent type declaration.
-
- auto DeclHasUnusedAttr = [](const QualType &T) {
- if (const TagDecl *TD = T->getAsTagDecl())
- return TD->hasAttr<UnusedAttr>();
- if (const TypedefType *TDT = T->getAs<TypedefType>())
- return TDT->getDecl()->hasAttr<UnusedAttr>();
- return false;
- };
-
- if (!FD->isImplicit() && FD->getDeclName() &&
- FD->getAccess() == AS_private &&
- !FD->hasAttr<UnusedAttr>() &&
- !FD->getParent()->isDependentContext() &&
- !DeclHasUnusedAttr(FD->getType()) &&
- !InitializationHasSideEffects(*FD))
- UnusedPrivateFields.insert(FD);
+ UnusedPrivateFields.insert(FD);
}
}
diff --git a/clang/test/SemaCXX/warn-unused-private-field.cpp b/clang/test/SemaCXX/warn-unused-private-field.cpp
index 0cc6f687f1b35f..93a285b159f740 100644
--- a/clang/test/SemaCXX/warn-unused-private-field.cpp
+++ b/clang/test/SemaCXX/warn-unused-private-field.cpp
@@ -329,3 +329,16 @@ class C {
MaybeUnusedTypedef t; // no-warning
};
}
+
+namespace GH62472 {
+class [[gnu::warn_unused]] S {
+public:
+ S();
+};
+
+class C {
+private:
+ const int i = 0; // expected-warning {{private field 'i' is not used}}
+ const S s; // expected-warning {{private field 's' is not used}}
+};
+}
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a-tarasyuk
commented
Dec 20, 2024
erichkeane
reviewed
Dec 20, 2024
tbaederr
reviewed
Jan 19, 2025
erichkeane
approved these changes
Jan 28, 2025
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erichkeane
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This LGTM and I think it does the behavior we want. Aaron to confirm?
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/73/builds/12607 Here is the relevant piece of the build log for the reference |
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Fixes #62472