erichkeane created this revision.
erichkeane added reviewers: aaron.ballman, chandlerc.
Herald added a project: clang.
EWG met on 7/18/19 and came to the conclusion that our initial intent
was to apply to constructors, so approved the paper and expected
implementers to use implementers discretion to backport this to previous
standards. ChandlerC was particularly vocal in wanting this.
The intent is to enable the library to start using this on the
constructors of scope_guard/lock_guard.
Repository:
rC Clang
https://reviews.llvm.org/D64914
Files:
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/lib/AST/Expr.cpp
clang/lib/Sema/SemaDeclAttr.cpp
clang/lib/Sema/SemaStmt.cpp
clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.nodiscard/p2.cpp
Index: clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.nodiscard/p2.cpp
===================================================================
--- clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.nodiscard/p2.cpp
+++ clang/test/CXX/dcl.dcl/dcl.attr/dcl.attr.nodiscard/p2.cpp
@@ -61,10 +61,27 @@
}
} // namespace PR31526
+namespace p1771 {
+ struct S {
+ [[nodiscard]] S();
+ [[gnu::pure]] S(int);
+ [[gnu::const]] S(double);
+ };
+ struct [[nodiscard]]Y{};
+ void usage() {
+ S(); // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
+ S(1); // expected-warning {{ignoring temporary created by a constructor declared with 'pure' attribute}}
+ S(2.2); // expected-warning {{ignoring temporary created by a constructor declared with 'const' attribute}}
+ Y(); // expected-warning {{expression result unused}}
+ }
+}; // namespace p1771
+
#ifdef EXT
// expected-warning@4 {{use of the 'nodiscard' attribute is a C++17 extension}}
// expected-warning@8 {{use of the 'nodiscard' attribute is a C++17 extension}}
// expected-warning@11 {{use of the 'nodiscard' attribute is a C++17 extension}}
// expected-warning@12 {{use of the 'nodiscard' attribute is a C++17 extension}}
// expected-warning@28 {{use of the 'nodiscard' attribute is a C++17 extension}}
+// expected-warning@66 {{use of the 'nodiscard' attribute is a C++17 extension}}
+// expected-warning@70 {{use of the 'nodiscard' attribute is a C++17 extension}}
#endif
Index: clang/lib/Sema/SemaStmt.cpp
===================================================================
--- clang/lib/Sema/SemaStmt.cpp
+++ clang/lib/Sema/SemaStmt.cpp
@@ -279,6 +279,21 @@
return;
}
}
+ } else if (const auto *CE = dyn_cast<CXXConstructExpr>(E)) {
+ if (const CXXConstructorDecl *Ctor = CE->getConstructor()) {
+ if (const Attr *A = Ctor->getAttr<WarnUnusedResultAttr>()) {
+ Diag(Loc, diag::warn_unused_constructor) << A << R1 << R2;
+ return;
+ }
+ if (const Attr *A = Ctor->getAttr<PureAttr>()) {
+ Diag(Loc, diag::warn_unused_constructor) << A << R1 << R2;
+ return;
+ }
+ if (const Attr *A = Ctor->getAttr<ConstAttr>()) {
+ Diag(Loc, diag::warn_unused_constructor) << A << R1 << R2;
+ return;
+ }
+ }
} else if (ShouldSuppress)
return;
Index: clang/lib/Sema/SemaDeclAttr.cpp
===================================================================
--- clang/lib/Sema/SemaDeclAttr.cpp
+++ clang/lib/Sema/SemaDeclAttr.cpp
@@ -2831,7 +2831,8 @@
static void handleWarnUnusedResult(Sema &S, Decl *D, const ParsedAttr &AL) {
if (D->getFunctionType() &&
- D->getFunctionType()->getReturnType()->isVoidType()) {
+ D->getFunctionType()->getReturnType()->isVoidType() &&
+ !isa<CXXConstructorDecl>(D)) {
S.Diag(AL.getLoc(), diag::warn_attribute_void_function_method) << AL << 0;
return;
}
Index: clang/lib/AST/Expr.cpp
===================================================================
--- clang/lib/AST/Expr.cpp
+++ clang/lib/AST/Expr.cpp
@@ -2563,13 +2563,30 @@
case CXXTemporaryObjectExprClass:
case CXXConstructExprClass: {
if (const CXXRecordDecl *Type = getType()->getAsCXXRecordDecl()) {
- if (Type->hasAttr<WarnUnusedAttr>()) {
+ if (Type->hasAttr<WarnUnusedAttr>() ||
+ Type->hasAttr<WarnUnusedResultAttr>()) {
WarnE = this;
Loc = getBeginLoc();
R1 = getSourceRange();
return true;
}
}
+
+ const auto *CE = cast<CXXConstructExpr>(this);
+ if (const CXXConstructorDecl *Ctor = CE->getConstructor()) {
+ if (Ctor->hasAttr<WarnUnusedResultAttr>() || Ctor->hasAttr<PureAttr>() ||
+ Ctor->hasAttr<ConstAttr>()) {
+ 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;
}
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -7426,6 +7426,9 @@
def warn_unused_call : Warning<
"ignoring return value of function declared with %0 attribute">,
InGroup<UnusedValue>;
+def warn_unused_constructor : Warning<
+ "ignoring temporary created by a constructor declared with %0 attribute">,
+ InGroup<UnusedValue>;
def warn_side_effects_unevaluated_context : Warning<
"expression with side effects has no effect in an unevaluated context">,
InGroup<UnevaluatedExpression>;
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