r262872 - Implement support for [[nodiscard]] in C++1z that is based off existing support for warn_unused_result, and treat it as an extension pre-C++1z. This also means extending the existing warn_unused_result attribute so that it can be placed on an enum as well as a class.
Aaron Ballman via cfe-commits
cfe-commits at lists.llvm.org
Mon Mar 7 14:44:56 PST 2016
Author: aaronballman
Date: Mon Mar 7 16:44:55 2016
New Revision: 262872
URL: http://llvm.org/viewvc/llvm-project?rev=262872&view=rev
Log:
Implement support for [[nodiscard]] in C++1z that is based off existing support for warn_unused_result, and treat it as an extension pre-C++1z. This also means extending the existing warn_unused_result attribute so that it can be placed on an enum as well as a class.
Added:
cfe/trunk/test/SemaCXX/nodiscard.cpp
Modified:
cfe/trunk/include/clang/AST/Decl.h
cfe/trunk/include/clang/Basic/Attr.td
cfe/trunk/include/clang/Basic/AttrDocs.td
cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
cfe/trunk/include/clang/Sema/AttributeList.h
cfe/trunk/lib/AST/Decl.cpp
cfe/trunk/lib/Parse/ParseDeclCXX.cpp
cfe/trunk/lib/Sema/SemaDeclAttr.cpp
cfe/trunk/lib/Sema/SemaStmt.cpp
cfe/trunk/test/Sema/unused-expr.c
cfe/trunk/test/SemaObjC/method-warn-unused-attribute.m
cfe/trunk/www/cxx_status.html
Modified: cfe/trunk/include/clang/AST/Decl.h
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/AST/Decl.h?rev=262872&r1=262871&r2=262872&view=diff
==============================================================================
--- cfe/trunk/include/clang/AST/Decl.h (original)
+++ cfe/trunk/include/clang/AST/Decl.h Mon Mar 7 16:44:55 2016
@@ -2025,12 +2025,16 @@ public:
return getType()->getAs<FunctionType>()->getCallResultType(getASTContext());
}
+ /// \brief Returns the WarnUnusedResultAttr that is either declared on this
+ /// function, or its return type declaration.
+ const Attr *getUnusedResultAttr() const;
+
/// \brief Returns true if this function or its return type has the
/// warn_unused_result attribute. If the return type has the attribute and
/// this function is a method of the return type's class, then false will be
/// returned to avoid spurious warnings on member methods such as assignment
/// operators.
- bool hasUnusedResultAttr() const;
+ bool hasUnusedResultAttr() const { return getUnusedResultAttr() != nullptr; }
/// \brief Returns the storage class as written in the source. For the
/// computed linkage of symbol, see getLinkage.
Modified: cfe/trunk/include/clang/Basic/Attr.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/Attr.td?rev=262872&r1=262871&r2=262872&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/Attr.td (original)
+++ cfe/trunk/include/clang/Basic/Attr.td Mon Mar 7 16:44:55 2016
@@ -1537,11 +1537,12 @@ def WarnUnused : InheritableAttr {
}
def WarnUnusedResult : InheritableAttr {
- let Spellings = [GCC<"warn_unused_result">,
- CXX11<"clang", "warn_unused_result">];
- let Subjects = SubjectList<[ObjCMethod, CXXRecord, FunctionLike], WarnDiag,
- "ExpectedFunctionMethodOrClass">;
- let Documentation = [Undocumented];
+ let Spellings = [CXX11<"", "nodiscard", 201603>,
+ CXX11<"clang", "warn_unused_result">,
+ GCC<"warn_unused_result">];
+ let Subjects = SubjectList<[ObjCMethod, Enum, CXXRecord, FunctionLike],
+ WarnDiag, "ExpectedFunctionMethodEnumOrClass">;
+ let Documentation = [WarnUnusedResultsDocs];
}
def Weak : InheritableAttr {
Modified: cfe/trunk/include/clang/Basic/AttrDocs.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/AttrDocs.td?rev=262872&r1=262871&r2=262872&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/AttrDocs.td (original)
+++ cfe/trunk/include/clang/Basic/AttrDocs.td Mon Mar 7 16:44:55 2016
@@ -729,6 +729,31 @@ When one method overrides another, the o
}];
}
+def WarnUnusedResultsDocs : Documentation {
+ let Category = DocCatFunction;
+ let Heading = "nodiscard, warn_unused_result, clang::warn_unused_result, gnu::warn_unused_result";
+ let Content = [{
+Clang supports the ability to diagnose when the results of a function call
+expression are discarded under suspicious circumstances. A diagnostic is
+generated when a function or its return type is marked with ``[[nodiscard]]``
+(or ``__attribute__((warn_unused_result))``) and the function call appears as a
+potentially-evaluated discarded-value expression that is not explicitly cast to
+`void`.
+
+.. code-block: c++
+ struct [[nodiscard]] error_info { /*...*/ };
+ error_info enable_missile_safety_mode();
+
+ void launch_missiles();
+ void test_missiles() {
+ enable_missile_safety_mode(); // diagnoses
+ launch_missiles();
+ }
+ error_info &foo();
+ void f() { foo(); } // Does not diagnose, error_info is a reference.
+ }];
+}
+
def FallthroughDocs : Documentation {
let Category = DocCatStmt;
let Content = [{
Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=262872&r1=262871&r2=262872&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
+++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Mon Mar 7 16:44:55 2016
@@ -2475,7 +2475,7 @@ def warn_attribute_wrong_decl_type : War
"variables, functions and classes|Objective-C protocols|"
"functions and global variables|structs, unions, and typedefs|structs and typedefs|"
"interface or protocol declarations|kernel functions|non-K&R-style functions|"
- "variables, enums, fields and typedefs}1">,
+ "variables, enums, fields and typedefs|functions, methods, enums, and classes}1">,
InGroup<IgnoredAttributes>;
def err_attribute_wrong_decl_type : Error<warn_attribute_wrong_decl_type.Text>;
def warn_type_attribute_wrong_type : Warning<
@@ -6587,11 +6587,13 @@ def warn_side_effects_typeid : Warning<
"expression with side effects will be evaluated despite being used as an "
"operand to 'typeid'">, InGroup<PotentiallyEvaluatedExpression>;
def warn_unused_result : Warning<
- "ignoring return value of function declared with warn_unused_result "
- "attribute">, InGroup<DiagGroup<"unused-result">>;
+ "ignoring return value of function declared with %0 attribute">,
+ InGroup<DiagGroup<"unused-result">>;
def warn_unused_volatile : Warning<
"expression result unused; assign into a variable to force a volatile load">,
InGroup<DiagGroup<"unused-volatile-lvalue">>;
+def ext_nodiscard_attr_is_a_cxx1z_extension : ExtWarn<
+ "use of the 'nodiscard' attribute is a C++1z extension">, InGroup<CXX1z>;
def warn_unused_comparison : Warning<
"%select{%select{|in}1equality|relational}0 comparison result unused">,
Modified: cfe/trunk/include/clang/Sema/AttributeList.h
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Sema/AttributeList.h?rev=262872&r1=262871&r2=262872&view=diff
==============================================================================
--- cfe/trunk/include/clang/Sema/AttributeList.h (original)
+++ cfe/trunk/include/clang/Sema/AttributeList.h Mon Mar 7 16:44:55 2016
@@ -893,7 +893,8 @@ enum AttributeDeclKind {
ExpectedObjectiveCInterfaceOrProtocol,
ExpectedKernelFunction,
ExpectedFunctionWithProtoType,
- ExpectedVariableEnumFieldOrTypedef
+ ExpectedVariableEnumFieldOrTypedef,
+ ExpectedFunctionMethodEnumOrClass
};
} // end namespace clang
Modified: cfe/trunk/lib/AST/Decl.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/Decl.cpp?rev=262872&r1=262871&r2=262872&view=diff
==============================================================================
--- cfe/trunk/lib/AST/Decl.cpp (original)
+++ cfe/trunk/lib/AST/Decl.cpp Mon Mar 7 16:44:55 2016
@@ -2935,16 +2935,22 @@ SourceRange FunctionDecl::getReturnTypeS
return RTRange;
}
-bool FunctionDecl::hasUnusedResultAttr() const {
+const Attr *FunctionDecl::getUnusedResultAttr() const {
QualType RetType = getReturnType();
if (RetType->isRecordType()) {
const CXXRecordDecl *Ret = RetType->getAsCXXRecordDecl();
const auto *MD = dyn_cast<CXXMethodDecl>(this);
- if (Ret && Ret->hasAttr<WarnUnusedResultAttr>() &&
- !(MD && MD->getCorrespondingMethodInClass(Ret, true)))
- return true;
+ if (Ret && !(MD && MD->getCorrespondingMethodInClass(Ret, true))) {
+ if (const auto *R = Ret->getAttr<WarnUnusedResultAttr>())
+ return R;
+ }
+ } else if (const auto *ET = RetType->getAs<EnumType>()) {
+ if (const EnumDecl *ED = ET->getDecl()) {
+ if (const auto *R = ED->getAttr<WarnUnusedResultAttr>())
+ return R;
+ }
}
- return hasAttr<WarnUnusedResultAttr>();
+ return getAttr<WarnUnusedResultAttr>();
}
/// \brief For an inline function definition in C, or for a gnu_inline function
Modified: cfe/trunk/lib/Parse/ParseDeclCXX.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Parse/ParseDeclCXX.cpp?rev=262872&r1=262871&r2=262872&view=diff
==============================================================================
--- cfe/trunk/lib/Parse/ParseDeclCXX.cpp (original)
+++ cfe/trunk/lib/Parse/ParseDeclCXX.cpp Mon Mar 7 16:44:55 2016
@@ -3635,7 +3635,8 @@ static bool IsBuiltInOrStandardCXX11Attr
case AttributeList::AT_FallThrough:
case AttributeList::AT_CXX11NoReturn:
return true;
-
+ case AttributeList::AT_WarnUnusedResult:
+ return !ScopeName && AttrName->getName().equals("nodiscard");
default:
return false;
}
Modified: cfe/trunk/lib/Sema/SemaDeclAttr.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDeclAttr.cpp?rev=262872&r1=262871&r2=262872&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaDeclAttr.cpp (original)
+++ cfe/trunk/lib/Sema/SemaDeclAttr.cpp Mon Mar 7 16:44:55 2016
@@ -2463,6 +2463,12 @@ static void handleWarnUnusedResult(Sema
return;
}
+ // If this is spelled as the standard C++1z attribute, but not in C++1z, warn
+ // about using it as an extension.
+ if (!S.getLangOpts().CPlusPlus1z && Attr.isCXX11Attribute() &&
+ !Attr.getScopeName())
+ S.Diag(Attr.getLoc(), diag::ext_nodiscard_attr_is_a_cxx1z_extension);
+
D->addAttr(::new (S.Context)
WarnUnusedResultAttr(Attr.getRange(), S.Context,
Attr.getAttributeSpellingListIndex()));
Modified: cfe/trunk/lib/Sema/SemaStmt.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaStmt.cpp?rev=262872&r1=262871&r2=262872&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaStmt.cpp (original)
+++ cfe/trunk/lib/Sema/SemaStmt.cpp Mon Mar 7 16:44:55 2016
@@ -249,10 +249,10 @@ void Sema::DiagnoseUnusedExprResult(cons
// is written in a macro body, only warn if it has the warn_unused_result
// attribute.
if (const Decl *FD = CE->getCalleeDecl()) {
- const FunctionDecl *Func = dyn_cast<FunctionDecl>(FD);
- if (Func ? Func->hasUnusedResultAttr()
- : FD->hasAttr<WarnUnusedResultAttr>()) {
- Diag(Loc, diag::warn_unused_result) << R1 << R2;
+ if (const Attr *A = isa<FunctionDecl>(FD)
+ ? cast<FunctionDecl>(FD)->getUnusedResultAttr()
+ : FD->getAttr<WarnUnusedResultAttr>()) {
+ Diag(Loc, diag::warn_unused_result) << A << R1 << R2;
return;
}
if (ShouldSuppress)
@@ -276,8 +276,8 @@ void Sema::DiagnoseUnusedExprResult(cons
}
const ObjCMethodDecl *MD = ME->getMethodDecl();
if (MD) {
- if (MD->hasAttr<WarnUnusedResultAttr>()) {
- Diag(Loc, diag::warn_unused_result) << R1 << R2;
+ if (const auto *A = MD->getAttr<WarnUnusedResultAttr>()) {
+ Diag(Loc, diag::warn_unused_result) << A << R1 << R2;
return;
}
}
Modified: cfe/trunk/test/Sema/unused-expr.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/unused-expr.c?rev=262872&r1=262871&r2=262872&view=diff
==============================================================================
--- cfe/trunk/test/Sema/unused-expr.c (original)
+++ cfe/trunk/test/Sema/unused-expr.c Mon Mar 7 16:44:55 2016
@@ -76,7 +76,7 @@ void t4(int a) {
// rdar://7186119
int t5f(void) __attribute__((warn_unused_result));
void t5() {
- t5f(); // expected-warning {{ignoring return value of function declared with warn_unused_result}}
+ t5f(); // expected-warning {{ignoring return value of function declared with 'warn_unused_result' attribute}}
}
@@ -88,11 +88,11 @@ int t6() {
if (fn1() < 0 || fn2(2,1) < 0 || fn3(2) < 0) // no warnings
return -1;
- fn1(); // expected-warning {{ignoring return value of function declared with warn_unused_result attribute}}
+ fn1(); // expected-warning {{ignoring return value of function declared with 'warn_unused_result' attribute}}
fn2(92, 21); // expected-warning {{ignoring return value of function declared with pure attribute}}
fn3(42); // expected-warning {{ignoring return value of function declared with const attribute}}
__builtin_abs(0); // expected-warning {{ignoring return value of function declared with const attribute}}
- (void)0, fn1(); // expected-warning {{ignoring return value of function declared with warn_unused_result attribute}}
+ (void)0, fn1(); // expected-warning {{ignoring return value of function declared with 'warn_unused_result' attribute}}
return 0;
}
@@ -101,7 +101,7 @@ int t7 __attribute__ ((warn_unused_resul
// PR4010
int (*fn4)(void) __attribute__ ((warn_unused_result));
void t8() {
- fn4(); // expected-warning {{ignoring return value of function declared with warn_unused_result attribute}}
+ fn4(); // expected-warning {{ignoring return value of function declared with 'warn_unused_result' attribute}}
}
void t9() __attribute__((warn_unused_result)); // expected-warning {{attribute 'warn_unused_result' cannot be applied to functions without return value}}
Added: cfe/trunk/test/SemaCXX/nodiscard.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/nodiscard.cpp?rev=262872&view=auto
==============================================================================
--- cfe/trunk/test/SemaCXX/nodiscard.cpp (added)
+++ cfe/trunk/test/SemaCXX/nodiscard.cpp Mon Mar 7 16:44:55 2016
@@ -0,0 +1,33 @@
+// RUN: %clang_cc1 -fsyntax-only -std=c++1z -verify %s
+// RUN: %clang_cc1 -fsyntax-only -std=c++11 -verify -DEXT %s
+
+#if !defined(EXT)
+static_assert(__has_cpp_attribute(nodiscard) == 201603);
+
+struct [[nodiscard]] S {};
+S get_s();
+S& get_s_ref();
+
+enum [[nodiscard]] E {};
+E get_e();
+
+[[nodiscard]] int get_i();
+
+void f() {
+ get_s(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ get_i(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ get_e(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ // Okay, warnings are not encouraged
+ get_s_ref();
+ (void)get_s();
+ (void)get_i();
+ (void)get_e();
+}
+
+[[nodiscard nodiscard]] int wrong1(); // expected-error {{attribute 'nodiscard' cannot appear multiple times in an attribute specifier}}
+
+namespace [[nodiscard]] N {} // expected-warning {{'nodiscard' attribute only applies to functions, methods, enums, and classes}}
+#else
+struct [[nodiscard]] S {}; // expected-warning {{use of the 'nodiscard' attribute is a C++1z extension}}
+#endif // EXT
Modified: cfe/trunk/test/SemaObjC/method-warn-unused-attribute.m
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaObjC/method-warn-unused-attribute.m?rev=262872&r1=262871&r2=262872&view=diff
==============================================================================
--- cfe/trunk/test/SemaObjC/method-warn-unused-attribute.m (original)
+++ cfe/trunk/test/SemaObjC/method-warn-unused-attribute.m Mon Mar 7 16:44:55 2016
@@ -9,8 +9,8 @@
void foo(INTF *a) {
[a garf];
- [a fee]; // expected-warning {{ignoring return value of function declared with warn_unused_result attribute}}
- [INTF c]; // expected-warning {{ignoring return value of function declared with warn_unused_result attribute}}
+ [a fee]; // expected-warning {{ignoring return value of function declared with 'warn_unused_result' attribute}}
+ [INTF c]; // expected-warning {{ignoring return value of function declared with 'warn_unused_result' attribute}}
}
Modified: cfe/trunk/www/cxx_status.html
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/www/cxx_status.html?rev=262872&r1=262871&r2=262872&view=diff
==============================================================================
--- cfe/trunk/www/cxx_status.html (original)
+++ cfe/trunk/www/cxx_status.html Mon Mar 7 16:44:55 2016
@@ -634,7 +634,7 @@ as the draft C++1z standard evolves.</p>
<tr>
<td><tt>[[nodiscard]]</tt> attribute</td>
<td><a href="http://wg21.link/p0189r1">P0189R1</a></td>
- <td class="none" align="center">No</td>
+ <td class="full" align="center">SVN</td>
</tr>
<tr>
<td><tt>[[maybe_unused]]</tt> attribute</td>
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