[PATCH] D102122: Support warn_unused_result on typedefs

[David Blaikie via Phabricator via cfe-commits]

dblaikie created this revision.
dblaikie added a reviewer: aaron.ballman.
dblaikie requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

While it's not as robust as using the attribute on enums/classes (the
type information may be lost through a function pointer, a declaration
or use of the underlying type without using the typedef, etc) but I
think there's still value in being able to attribute a typedef and have
all return types written with that typedef pick up the
warn_unused_result behavior.

Specifically I'd like to be able to annotate LLVMErrorRef (a wrapper for
llvm::Error used in the C API - the underlying type is a raw pointer, so
it can't be attributed itself) to reduce the chance of unhandled errors.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D102122

Files:
  clang/include/clang/Basic/Attr.td
  clang/lib/AST/Expr.cpp
  clang/test/SemaCXX/warn-unused-result.cpp


Index: clang/test/SemaCXX/warn-unused-result.cpp
===================================================================
--- clang/test/SemaCXX/warn-unused-result.cpp
+++ clang/test/SemaCXX/warn-unused-result.cpp
@@ -254,3 +254,15 @@
 
 void i([[nodiscard]] bool (*fp)()); // expected-warning {{'nodiscard' attribute only applies to functions, classes, or enumerations}}
 }
+
+namespace unused_typedef_result {
+[[clang::warn_unused_result]] typedef void *p;
+p f1();
+void f2() {
+  f1(); // expected-warning {{ignoring return value}}
+  void *(*p1)();
+  p1(); // no warning
+  p (*p2)();
+  p2(); // expected-warning {{ignoring return value}}
+}
+}
Index: clang/lib/AST/Expr.cpp
===================================================================
--- clang/lib/AST/Expr.cpp
+++ clang/lib/AST/Expr.cpp
@@ -1413,6 +1413,10 @@
     if (const auto *A = TD->getAttr<WarnUnusedResultAttr>())
       return A;
 
+  if (const auto *TD = getCallReturnType(Ctx)->getAs<TypedefType>())
+    if (const auto *A = TD->getDecl()->getAttr<WarnUnusedResultAttr>())
+      return A;
+
   // Otherwise, see if the callee is marked nodiscard and return that attribute
   // instead.
   const Decl *D = getCalleeDecl();
Index: clang/include/clang/Basic/Attr.td
===================================================================
--- clang/include/clang/Basic/Attr.td
+++ clang/include/clang/Basic/Attr.td
@@ -2812,7 +2812,7 @@
                    C2x<"", "nodiscard", 201904>,
                    CXX11<"clang", "warn_unused_result">,
                    GCC<"warn_unused_result">];
-  let Subjects = SubjectList<[ObjCMethod, Enum, Record, FunctionLike]>;
+  let Subjects = SubjectList<[ObjCMethod, Enum, Record, FunctionLike, TypedefName]>;
   let Args = [StringArgument<"Message", 1>];
   let Documentation = [WarnUnusedResultsDocs];
   let AdditionalMembers = [{


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