Diagnose an unused result from a call through a function pointer whose return type is marked [[nodiscard]].
When a function returns a type and that type was declared [[nodiscard]], we diagnose any unused results from that call as though the function were marked nodiscard. The same behavior should apply to calls through a function pointer.
This addresses PR31526.
llvm-svn: 350317
diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index 6aa1199..0775ff5 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -1412,6 +1412,19 @@
return FnType->getReturnType();
}
+const Attr *CallExpr::getUnusedResultAttr(const ASTContext &Ctx) const {
+ // 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 auto *A = TD->getAttr<WarnUnusedResultAttr>())
+ return A;
+
+ // Otherwise, see if the callee is marked nodiscard and return that attribute
+ // instead.
+ const Decl *D = getCalleeDecl();
+ return D ? D->getAttr<WarnUnusedResultAttr>() : nullptr;
+}
+
SourceLocation CallExpr::getBeginLoc() const {
if (isa<CXXOperatorCallExpr>(this))
return cast<CXXOperatorCallExpr>(this)->getBeginLoc();
@@ -2323,16 +2336,12 @@
// If this is a direct call, get the callee.
const CallExpr *CE = cast<CallExpr>(this);
if (const Decl *FD = CE->getCalleeDecl()) {
- const FunctionDecl *Func = dyn_cast<FunctionDecl>(FD);
- bool HasWarnUnusedResultAttr = Func ? Func->hasUnusedResultAttr()
- : FD->hasAttr<WarnUnusedResultAttr>();
-
// If the callee has attribute pure, const, or warn_unused_result, warn
// about it. void foo() { strlen("bar"); } should warn.
//
// Note: If new cases are added here, DiagnoseUnusedExprResult should be
// updated to match for QoI.
- if (HasWarnUnusedResultAttr ||
+ if (CE->hasUnusedResultAttr(Ctx) ||
FD->hasAttr<PureAttr>() || FD->hasAttr<ConstAttr>()) {
WarnE = this;
Loc = CE->getCallee()->getBeginLoc();