https://github.com/halbi2 updated
https://github.com/llvm/llvm-project/pull/139651
>From 1efa70c6702f7506580a5b8c49ea3df779d31163 Mon Sep 17 00:00:00 2001
From: halbi2 <hehira...@gmail.com>
Date: Mon, 18 Aug 2025 21:46:47 -0400
Subject: [PATCH 1/2] [clang] [test] Better test coverage for nodiscard
attributes
---
clang/test/Sema/c2x-nodiscard.c | 17 +++++
clang/test/SemaCXX/warn-unused-result.cpp | 85 +++++++++++++++++++++++
clang/test/SemaObjC/attr-nodiscard.m | 9 ++-
clang/test/SemaObjCXX/attr-nodiscard.mm | 9 ++-
4 files changed, 118 insertions(+), 2 deletions(-)
diff --git a/clang/test/Sema/c2x-nodiscard.c b/clang/test/Sema/c2x-nodiscard.c
index e2537bcf1d29d..852c74721693b 100644
--- a/clang/test/Sema/c2x-nodiscard.c
+++ b/clang/test/Sema/c2x-nodiscard.c
@@ -41,6 +41,10 @@ void f2(void) {
(void)get_s3();
(void)get_i();
(void)get_e();
+
+ One; // expected-warning {{expression result unused}}
+ (enum E2)(0); // expected-warning {{expression result unused}}
+ (struct S4){1}; // expected-warning {{expression result unused}}
}
struct [[nodiscard]] error_info{
@@ -60,3 +64,16 @@ void GH104391() {
#define M (unsigned int) f3()
M; // expected-warning {{ignoring return value of function declared with
'nodiscard' attribute}}
}
+
+[[nodiscard]] typedef int NoDInt; // expected-warning {{'[[nodiscard]]'
attribute ignored when applied to a typedef}}
+typedef __attribute__((warn_unused)) int WUInt; // expected-warning
{{'warn_unused' attribute only applies to structs, unions, and classes}}
+typedef __attribute__((warn_unused_result)) int WURInt;
+NoDInt get_nodint();
+WUInt get_wuint();
+WURInt get_wurint();
+
+void f4(void) {
+ get_nodint(); // no warning because attribute is ignored
+ get_wuint(); // no warning because attribute is ignored
+ get_wurint(); // expected-warning {{ignoring return value of type 'WURInt'
declared with 'warn_unused_result' attribute}}
+}
diff --git a/clang/test/SemaCXX/warn-unused-result.cpp
b/clang/test/SemaCXX/warn-unused-result.cpp
index 1f7913f1aa994..bd46fdfd57061 100644
--- a/clang/test/SemaCXX/warn-unused-result.cpp
+++ b/clang/test/SemaCXX/warn-unused-result.cpp
@@ -407,3 +407,88 @@ void doGccThings() {
}
} // namespace BuildStringOnClangScope
+
+namespace candiscard {
+
+struct [[nodiscard]] NoDiscard {
+ [[nodiscard]] NoDiscard(int);
+ NoDiscard(const char *);
+};
+
+struct [[gnu::warn_unused]] WarnUnused {
+ [[gnu::warn_unused]] WarnUnused(int); // expected-warning
{{'gnu::warn_unused' attribute only applies to structs, unions, and classes}}
+ WarnUnused(const char*);
+};
+
+struct [[gnu::warn_unused_result]] WarnUnusedResult {
+ [[gnu::warn_unused_result]] WarnUnusedResult(int);
+ WarnUnusedResult(const char*);
+};
+
+NoDiscard return_nodiscard();
+WarnUnused return_warnunused();
+WarnUnusedResult return_warnunusedresult();
+
+NoDiscard (*p_return_nodiscard)();
+WarnUnused (*p_return_warnunused)();
+WarnUnusedResult (*p_return_warnunusedresult)();
+
+NoDiscard (*(*pp_return_nodiscard)())();
+WarnUnused (*(*pp_return_warnunused)())();
+WarnUnusedResult (*(*pp_return_warnunusedresult)())();
+
+template <class T> T from_a_template();
+
+void test() {
+ // Unused but named variables
+ NoDiscard unused_variable1(1); // no warning
+ NoDiscard unused_variable2(""); // no warning
+ WarnUnused unused_variable3(1); // no warning
+ WarnUnused unused_variable4(""); // no warning
+ WarnUnusedResult unused_variable5(1); // no warning
+ WarnUnusedResult unused_variable6(""); // no warning
+
+ // Constructor return values
+ NoDiscard(1); // expected-warning {{ignoring temporary created by a
constructor declared with 'nodiscard' attribute}}
+ NoDiscard(""); // expected-warning {{ignoring temporary of type
'NoDiscard' declared with 'nodiscard' attribute}}
+ WarnUnused(1); // expected-warning {{expression result unused}}
+ WarnUnused(""); // expected-warning {{expression result unused}}
+ WarnUnusedResult(1); // expected-warning {{ignoring temporary created by a
constructor declared with 'gnu::warn_unused_result' attribute}}
+ WarnUnusedResult(""); // expected-warning {{ignoring temporary of type
'WarnUnusedResult' declared with 'gnu::warn_unused_result' attribute}}
+
+ NoDiscard{1}; // expected-warning {{ignoring temporary created by a
constructor declared with 'nodiscard' attribute}}
+ NoDiscard{""}; // expected-warning {{ignoring temporary of type
'NoDiscard' declared with 'nodiscard' attribute}}
+ WarnUnused{1}; // expected-warning {{expression result unused}}
+ WarnUnused{""}; // expected-warning {{expression result unused}}
+ WarnUnusedResult{1}; // expected-warning {{ignoring temporary created by a
constructor declared with 'gnu::warn_unused_result' attribute}}
+ WarnUnusedResult{""}; // expected-warning {{ignoring temporary of type
'WarnUnusedResult' declared with 'gnu::warn_unused_result' attribute}}
+
+ static_cast<NoDiscard>(1); // expected-warning {{ignoring temporary
created by a constructor declared with 'nodiscard' attribute}}
+ static_cast<NoDiscard>(""); // expected-warning {{ignoring temporary
of type 'NoDiscard' declared with 'nodiscard' attribute}}
+ static_cast<WarnUnused>(1); // expected-warning {{expression result
unused}}
+ static_cast<WarnUnused>(""); // expected-warning {{expression result
unused}}
+ static_cast<WarnUnusedResult>(1); // expected-warning {{ignoring temporary
created by a constructor declared with 'gnu::warn_unused_result' attribute}}
+ static_cast<WarnUnusedResult>(""); // expected-warning {{ignoring temporary
of type 'WarnUnusedResult' declared with 'gnu::warn_unused_result' attribute}}
+
+ // Function return values
+ return_nodiscard(); // expected-warning {{ignoring return value of type
'NoDiscard' declared with 'nodiscard' attribute}}
+ return_warnunused(); // no warning
+ return_warnunusedresult(); // expected-warning {{ignoring return value of
type 'WarnUnusedResult' declared with 'gnu::warn_unused_result' attribute}}
+
+ // Function pointer return values
+ p_return_nodiscard(); // expected-warning {{ignoring return value of type
'NoDiscard' declared with 'nodiscard' attribute}}
+ p_return_warnunused(); // no warning
+ p_return_warnunusedresult(); // expected-warning {{ignoring return value of
type 'WarnUnusedResult' declared with 'gnu::warn_unused_result' attribute}}
+
+ // Function pointer expression return values
+ pp_return_nodiscard()(); // no warning: TODO
+ pp_return_warnunused()(); // no warning
+ pp_return_warnunusedresult()(); // no warning: TODO
+
+ // From a template
+ from_a_template<NoDiscard>(); // expected-warning {{ignoring return value of
type 'NoDiscard' declared with 'nodiscard' attribute}}
+ from_a_template<WarnUnused>(); // no warning
+ from_a_template<WarnUnusedResult>(); // expected-warning {{ignoring return
value of type 'WarnUnusedResult' declared with 'gnu::warn_unused_result'
attribute}}
+}
+
+} // namespace candiscard
diff --git a/clang/test/SemaObjC/attr-nodiscard.m
b/clang/test/SemaObjC/attr-nodiscard.m
index 6d04665da25ca..26bbd247d4a3d 100644
--- a/clang/test/SemaObjC/attr-nodiscard.m
+++ b/clang/test/SemaObjC/attr-nodiscard.m
@@ -4,6 +4,9 @@
typedef struct expected E;
+[[nodiscard]] typedef int NI; // expected-warning {{'[[nodiscard]]' attribute
ignored when applied to a typedef}}
+typedef __attribute__((warn_unused_result)) int WUR;
+
@interface INTF
- (int) a [[nodiscard]];
+ (int) b [[nodiscard]];
@@ -12,6 +15,8 @@ + (struct expected) d;
- (E) e;
+ (E) f;
- (void) g [[nodiscard]]; // expected-warning {{attribute 'nodiscard' cannot
be applied to Objective-C method without return value}}
+- (NI) h;
+- (WUR) i;
@end
void foo(INTF *a) {
@@ -21,5 +26,7 @@ void foo(INTF *a) {
[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];
+ [a g]; // no warning because g returns void
+ [a h]; // no warning because attribute is ignored when applied to a typedef
+ [a i]; // expected-warning {{ignoring return value of type 'WUR' declared
with 'warn_unused_result' attribute}}
}
diff --git a/clang/test/SemaObjCXX/attr-nodiscard.mm
b/clang/test/SemaObjCXX/attr-nodiscard.mm
index e1eefb74d3961..18d829632e428 100644
--- a/clang/test/SemaObjCXX/attr-nodiscard.mm
+++ b/clang/test/SemaObjCXX/attr-nodiscard.mm
@@ -5,6 +5,9 @@
using E = expected<int>;
+using NI [[nodiscard]] = int; // expected-warning {{'[[nodiscard]]' attribute
ignored when applied to a typedef}}
+using WURI [[clang::warn_unused_result]] = int;
+
@interface INTF
- (int) a [[nodiscard]];
+ (int) b [[nodiscard]];
@@ -13,6 +16,8 @@ + (int) b [[nodiscard]];
- (E) e;
+ (E) f;
- (void) g [[nodiscard]]; // expected-warning {{attribute 'nodiscard' cannot
be applied to Objective-C method without return value}}
+- (NI) h;
+- (WURI) i;
@end
void foo(INTF *a) {
@@ -22,5 +27,7 @@ void foo(INTF *a) {
[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];
+ [a g]; // no warning because g returns void
+ [a h]; // no warning because attribute is ignored
+ [a i]; // expected-warning {{ignoring return value of type 'WURI' declared
with 'clang::warn_unused_result' attribute}}
}
>From 23c5b44123961f252103d84b6f862242fdf54819 Mon Sep 17 00:00:00 2001
From: halbi2 <hehira...@gmail.com>
Date: Mon, 18 Aug 2025 21:47:32 -0400
Subject: [PATCH 2/2] [clang] [Sema] Enable nodiscard warnings for function
pointers
A call through a function pointer has no associated FunctionDecl,
but it still might have a nodiscard return type. Ensure there is
a codepath to emit the nodiscard warning in this case.
Fixes #142453
---
clang/lib/AST/Expr.cpp | 10 ++++++++++
clang/test/SemaCXX/warn-unused-result.cpp | 4 ++--
2 files changed, 12 insertions(+), 2 deletions(-)
diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index e14cff552c922..36e091915e0c8 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -2794,6 +2794,16 @@ bool Expr::isUnusedResultAWarning(const Expr *&WarnE,
SourceLocation &Loc,
return true;
}
}
+ if (CE->hasUnusedResultAttr(Ctx)) {
+ WarnE = this;
+ Loc = getBeginLoc();
+ R1 = getSourceRange();
+
+ if (unsigned NumArgs = CE->getNumArgs())
+ R2 = SourceRange(CE->getArg(0)->getBeginLoc(),
+ CE->getArg(NumArgs - 1)->getEndLoc());
+ return true;
+ }
return false;
}
diff --git a/clang/test/SemaCXX/warn-unused-result.cpp
b/clang/test/SemaCXX/warn-unused-result.cpp
index bd46fdfd57061..098817729efb1 100644
--- a/clang/test/SemaCXX/warn-unused-result.cpp
+++ b/clang/test/SemaCXX/warn-unused-result.cpp
@@ -481,9 +481,9 @@ void test() {
p_return_warnunusedresult(); // expected-warning {{ignoring return value of
type 'WarnUnusedResult' declared with 'gnu::warn_unused_result' attribute}}
// Function pointer expression return values
- pp_return_nodiscard()(); // no warning: TODO
+ pp_return_nodiscard()(); // expected-warning {{ignoring return value of type
'NoDiscard' declared with 'nodiscard' attribute}}
pp_return_warnunused()(); // no warning
- pp_return_warnunusedresult()(); // no warning: TODO
+ pp_return_warnunusedresult()(); // expected-warning {{ignoring return value
of type 'WarnUnusedResult' declared with 'gnu::warn_unused_result' attribute}}
// From a template
from_a_template<NoDiscard>(); // expected-warning {{ignoring return value of
type 'NoDiscard' declared with 'nodiscard' attribute}}
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