[clang] a63bbf2 - [clang] Diagnose [[nodiscard]] return types in Objective-C++ (#142541)
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Mon Jul 28 06:26:32 PDT 2025
Author: halbi2
Date: 2025-07-28T09:26:28-04:00
New Revision: a63bbf2f1e0d1e1367fb111290ba8d652572d724
URL: https://github.com/llvm/llvm-project/commit/a63bbf2f1e0d1e1367fb111290ba8d652572d724
DIFF: https://github.com/llvm/llvm-project/commit/a63bbf2f1e0d1e1367fb111290ba8d652572d724.diff
LOG: [clang] Diagnose [[nodiscard]] return types in Objective-C++ (#142541)
My solution was to copy-paste getUnusedResultAttr and
hasUnusedResultAttr from CallExpr into ObjCMessageExpr too.
Fixes #141504
Added:
clang/test/SemaObjC/attr-nodiscard.m
clang/test/SemaObjCXX/attr-nodiscard.mm
Modified:
clang/docs/ReleaseNotes.rst
clang/include/clang/AST/Expr.h
clang/include/clang/AST/ExprObjC.h
clang/lib/AST/Expr.cpp
clang/lib/AST/ExprObjC.cpp
clang/lib/Sema/SemaStmt.cpp
clang/test/SemaCXX/warn-unused-result.cpp
Removed:
################################################################################
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 95a0bbf734056..46290b6c39c9b 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -139,6 +139,9 @@ Bug Fixes to Compiler Builtins
Bug Fixes to Attribute Support
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+- ``[[nodiscard]]`` is now respected on Objective-C and Objective-C++ methods.
+ (#GH141504)
+
Bug Fixes to C++ Support
^^^^^^^^^^^^^^^^^^^^^^^^
- Diagnose binding a reference to ``*nullptr`` during constant evaluation. (#GH48665)
diff --git a/clang/include/clang/AST/Expr.h b/clang/include/clang/AST/Expr.h
index 523c0326d47ef..708c6e2925fd0 100644
--- a/clang/include/clang/AST/Expr.h
+++ b/clang/include/clang/AST/Expr.h
@@ -16,6 +16,7 @@
#include "clang/AST/APNumericStorage.h"
#include "clang/AST/APValue.h"
#include "clang/AST/ASTVector.h"
+#include "clang/AST/Attr.h"
#include "clang/AST/ComputeDependence.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclAccessPair.h"
@@ -262,6 +263,12 @@ class Expr : public ValueStmt {
SourceRange &R1, SourceRange &R2,
ASTContext &Ctx) const;
+ /// Returns the WarnUnusedResultAttr that is declared on the callee
+ /// or its return type declaration, together with a NamedDecl that
+ /// refers to the declaration the attribute is attached to.
+ static std::pair<const NamedDecl *, const WarnUnusedResultAttr *>
+ getUnusedResultAttrImpl(const Decl *Callee, QualType ReturnType);
+
/// isLValue - True if this expression is an "l-value" according to
/// the rules of the current language. C and C++ give somewhat
///
diff erent rules for this concept, but in general, the result of
@@ -3190,11 +3197,13 @@ class CallExpr : public Expr {
/// type.
QualType getCallReturnType(const ASTContext &Ctx) const;
- /// Returns the WarnUnusedResultAttr that is either declared on the called
- /// function, or its return type declaration, together with a NamedDecl that
- /// refers to the declaration the attribute is attached onto.
- std::pair<const NamedDecl *, const Attr *>
- getUnusedResultAttr(const ASTContext &Ctx) const;
+ /// Returns the WarnUnusedResultAttr that is declared on the callee
+ /// or its return type declaration, together with a NamedDecl that
+ /// refers to the declaration the attribute is attached to.
+ std::pair<const NamedDecl *, const WarnUnusedResultAttr *>
+ getUnusedResultAttr(const ASTContext &Ctx) const {
+ return getUnusedResultAttrImpl(getCalleeDecl(), getCallReturnType(Ctx));
+ }
/// Returns true if this call expression should warn on unused results.
bool hasUnusedResultAttr(const ASTContext &Ctx) const {
diff --git a/clang/include/clang/AST/ExprObjC.h b/clang/include/clang/AST/ExprObjC.h
index 8210be38608a6..b9232305f036a 100644
--- a/clang/include/clang/AST/ExprObjC.h
+++ b/clang/include/clang/AST/ExprObjC.h
@@ -13,6 +13,7 @@
#ifndef LLVM_CLANG_AST_EXPROBJC_H
#define LLVM_CLANG_AST_EXPROBJC_H
+#include "clang/AST/Attr.h"
#include "clang/AST/ComputeDependence.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclObjC.h"
@@ -1234,6 +1235,19 @@ class ObjCMessageExpr final
/// of `instancetype` (in that case it's an expression type).
QualType getCallReturnType(ASTContext &Ctx) const;
+ /// Returns the WarnUnusedResultAttr that is declared on the callee
+ /// or its return type declaration, together with a NamedDecl that
+ /// refers to the declaration the attribute is attached to.
+ std::pair<const NamedDecl *, const WarnUnusedResultAttr *>
+ getUnusedResultAttr(ASTContext &Ctx) const {
+ return getUnusedResultAttrImpl(getMethodDecl(), getCallReturnType(Ctx));
+ }
+
+ /// Returns true if this message send should warn on unused results.
+ bool hasUnusedResultAttr(ASTContext &Ctx) const {
+ return getUnusedResultAttr(Ctx).second != nullptr;
+ }
+
/// Source range of the receiver.
SourceRange getReceiverRange() const;
diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index 2e1a9a3d9ad63..d85655b1596f4 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -1629,20 +1629,20 @@ QualType CallExpr::getCallReturnType(const ASTContext &Ctx) const {
return FnType->getReturnType();
}
-std::pair<const NamedDecl *, const Attr *>
-CallExpr::getUnusedResultAttr(const ASTContext &Ctx) const {
+std::pair<const NamedDecl *, const WarnUnusedResultAttr *>
+Expr::getUnusedResultAttrImpl(const Decl *Callee, QualType ReturnType) {
// If the callee is marked nodiscard, return that attribute
- if (const Decl *D = getCalleeDecl())
- if (const auto *A = D->getAttr<WarnUnusedResultAttr>())
+ if (Callee != nullptr)
+ if (const auto *A = Callee->getAttr<WarnUnusedResultAttr>())
return {nullptr, A};
// If the return type is a struct, union, or enum that is marked nodiscard,
// then return the return type attribute.
- if (const TagDecl *TD = getCallReturnType(Ctx)->getAsTagDecl())
+ if (const TagDecl *TD = ReturnType->getAsTagDecl())
if (const auto *A = TD->getAttr<WarnUnusedResultAttr>())
return {TD, A};
- for (const auto *TD = getCallReturnType(Ctx)->getAs<TypedefType>(); TD;
+ for (const auto *TD = ReturnType->getAs<TypedefType>(); TD;
TD = TD->desugar()->getAs<TypedefType>())
if (const auto *A = TD->getDecl()->getAttr<WarnUnusedResultAttr>())
return {TD->getDecl(), A};
@@ -2844,12 +2844,11 @@ bool Expr::isUnusedResultAWarning(const Expr *&WarnE, SourceLocation &Loc,
return true;
}
- if (const ObjCMethodDecl *MD = ME->getMethodDecl())
- if (MD->hasAttr<WarnUnusedResultAttr>()) {
- WarnE = this;
- Loc = getExprLoc();
- return true;
- }
+ if (ME->hasUnusedResultAttr(Ctx)) {
+ WarnE = this;
+ Loc = getExprLoc();
+ return true;
+ }
return false;
}
diff --git a/clang/lib/AST/ExprObjC.cpp b/clang/lib/AST/ExprObjC.cpp
index 50d3a4474c4d7..83419a11c728f 100644
--- a/clang/lib/AST/ExprObjC.cpp
+++ b/clang/lib/AST/ExprObjC.cpp
@@ -12,6 +12,7 @@
#include "clang/AST/ExprObjC.h"
#include "clang/AST/ASTContext.h"
+#include "clang/AST/Attr.h"
#include "clang/AST/ComputeDependence.h"
#include "clang/AST/SelectorLocationsKind.h"
#include "clang/AST/Type.h"
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index f85826aecadf3..3f89843a9081a 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -295,8 +295,7 @@ void DiagnoseUnused(Sema &S, const Expr *E, std::optional<unsigned> DiagID) {
return;
auto [OffendingDecl, A] = CE->getUnusedResultAttr(S.Context);
- if (DiagnoseNoDiscard(S, OffendingDecl,
- cast_or_null<WarnUnusedResultAttr>(A), Loc, R1, R2,
+ if (DiagnoseNoDiscard(S, OffendingDecl, A, Loc, R1, R2,
/*isCtor=*/false))
return;
@@ -344,13 +343,11 @@ void DiagnoseUnused(Sema &S, const Expr *E, std::optional<unsigned> DiagID) {
S.Diag(Loc, diag::err_arc_unused_init_message) << R1;
return;
}
- const ObjCMethodDecl *MD = ME->getMethodDecl();
- if (MD) {
- if (DiagnoseNoDiscard(S, nullptr, MD->getAttr<WarnUnusedResultAttr>(),
- Loc, R1, R2,
- /*isCtor=*/false))
- return;
- }
+
+ auto [OffendingDecl, A] = ME->getUnusedResultAttr(S.Context);
+ if (DiagnoseNoDiscard(S, OffendingDecl, A, Loc, R1, R2,
+ /*isCtor=*/false))
+ return;
} else if (const PseudoObjectExpr *POE = dyn_cast<PseudoObjectExpr>(E)) {
const Expr *Source = POE->getSyntacticForm();
// Handle the actually selected call of an OpenMP specialized call.
diff --git a/clang/test/SemaCXX/warn-unused-result.cpp b/clang/test/SemaCXX/warn-unused-result.cpp
index fe7d5ea79e9a7..447654eccd563 100644
--- a/clang/test/SemaCXX/warn-unused-result.cpp
+++ b/clang/test/SemaCXX/warn-unused-result.cpp
@@ -365,6 +365,31 @@ void id_print_name() {
}
} // namespace GH117975
+namespace inheritance {
+// Test that [[nodiscard]] is not inherited by derived class types,
+// but is inherited by member functions
+struct [[nodiscard]] E {
+ [[nodiscard]] explicit E(int);
+ explicit E(const char*);
+ [[nodiscard]] int f();
+};
+struct F : E {
+ using E::E;
+};
+E e();
+F f();
+void test() {
+ e(); // expected-warning {{ignoring return value of type 'E' declared with 'nodiscard' attribute}}
+ f(); // no warning: derived class type does not inherit the attribute
+ E(1); // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
+ E("x"); // expected-warning {{ignoring temporary of type 'E' declared with 'nodiscard' attribute}}
+ F(1); // no warning: inherited constructor does not inherit the attribute either
+ F("x"); // no warning
+ e().f(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ f().f(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+}
+} // namespace inheritance
+
namespace BuildStringOnClangScope {
[[clang::warn_unused_result("Discarded result")]]
@@ -381,4 +406,4 @@ void doGccThings() {
makeGccTrue(); // expected-warning {{ignoring return value of function declared with 'gnu::warn_unused_result' attribute}}
}
-}
+} // namespace BuildStringOnClangScope
diff --git a/clang/test/SemaObjC/attr-nodiscard.m b/clang/test/SemaObjC/attr-nodiscard.m
new file mode 100644
index 0000000000000..6d04665da25ca
--- /dev/null
+++ b/clang/test/SemaObjC/attr-nodiscard.m
@@ -0,0 +1,25 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+struct [[nodiscard]] expected {};
+
+typedef struct expected E;
+
+ at interface INTF
+- (int) a [[nodiscard]];
++ (int) b [[nodiscard]];
+- (struct expected) c;
++ (struct expected) d;
+- (E) e;
++ (E) f;
+- (void) g [[nodiscard]]; // expected-warning {{attribute 'nodiscard' cannot be applied to Objective-C method without return value}}
+ at end
+
+void foo(INTF *a) {
+ [a a]; // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ [INTF b]; // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ [a c]; // expected-warning {{ignoring return value of type 'expected' declared with 'nodiscard' attribute}}
+ [INTF d]; // expected-warning {{ignoring return value of type 'expected' declared with 'nodiscard' attribute}}
+ [a e]; // expected-warning {{ignoring return value of type 'expected' declared with 'nodiscard' attribute}}
+ [INTF f]; // expected-warning {{ignoring return value of type 'expected' declared with 'nodiscard' attribute}}
+ [a g];
+}
diff --git a/clang/test/SemaObjCXX/attr-nodiscard.mm b/clang/test/SemaObjCXX/attr-nodiscard.mm
new file mode 100644
index 0000000000000..e1eefb74d3961
--- /dev/null
+++ b/clang/test/SemaObjCXX/attr-nodiscard.mm
@@ -0,0 +1,26 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+template<class T>
+struct [[nodiscard]] expected {};
+
+using E = expected<int>;
+
+ at interface INTF
+- (int) a [[nodiscard]];
++ (int) b [[nodiscard]];
+- (expected<int>) c;
++ (expected<int>) d;
+- (E) e;
++ (E) f;
+- (void) g [[nodiscard]]; // expected-warning {{attribute 'nodiscard' cannot be applied to Objective-C method without return value}}
+ at end
+
+void foo(INTF *a) {
+ [a a]; // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ [INTF b]; // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ [a c]; // expected-warning {{ignoring return value of type 'expected<int>' declared with 'nodiscard' attribute}}
+ [INTF d]; // expected-warning {{ignoring return value of type 'expected<int>' declared with 'nodiscard' attribute}}
+ [a e]; // expected-warning {{ignoring return value of type 'expected<int>' declared with 'nodiscard' attribute}}
+ [INTF f]; // expected-warning {{ignoring return value of type 'expected<int>' declared with 'nodiscard' attribute}}
+ [a g];
+}
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