[PATCH] D38205: [Sema] Warn on attribute nothrow conflicting with language specifiers

[Erich Keane via Phabricator via cfe-commits]

erichkeane created this revision.

I discovered it was possible to create a 'nothrow' noexcept(false)
function, which is both non-sensical as well as seemingly breaking.

This patch warns if attribute nothrow is used with anything besides "noexcept".

"noexcept(true)" isn't possible, because the noexcept decl isn't parsed until
later.


https://reviews.llvm.org/D38205

Files:
  include/clang/Basic/DiagnosticSemaKinds.td
  lib/Sema/SemaDeclAttr.cpp
  test/SemaCXX/warn-conflicting-nothrow-attr-exception-spec.cpp


Index: test/SemaCXX/warn-conflicting-nothrow-attr-exception-spec.cpp
===================================================================
--- /dev/null
+++ test/SemaCXX/warn-conflicting-nothrow-attr-exception-spec.cpp
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 %s -fcxx-exceptions -fsyntax-only -Wexceptions -verify -std=c++14
+
+struct S {
+  __attribute__((nothrow)) S() noexcept(true); 
+  __attribute__((nothrow)) void Func1() noexcept(false);
+  __attribute__((nothrow)) void Func2() throws();
+  __attribute__((nothrow)) void Func3() noexcept;
+};
Index: lib/Sema/SemaDeclAttr.cpp
===================================================================
--- lib/Sema/SemaDeclAttr.cpp
+++ lib/Sema/SemaDeclAttr.cpp
@@ -1969,6 +1969,25 @@
       attr.getRange(), S.Context, attr.getAttributeSpellingListIndex()));
 }
 
+static void handleNoThrowAttr(Sema &S, Decl *D, const AttributeList &attr) {
+  assert(isa<FunctionDecl>(D) && "attribute nothrow only valid on functions");
+
+  auto *FD = cast<FunctionDecl>(D);
+  const auto *FPT = FD->getType()->getAs<FunctionProtoType>();
+
+  if (FPT && FPT->hasExceptionSpec() &&
+      FPT->getExceptionSpecType() != EST_BasicNoexcept) {
+    S.Diag(attr.getLoc(),
+           diag::warn_nothrow_attr_disagrees_with_exception_specification);
+    S.Diag(FD->getExceptionSpecSourceRange().getBegin(),
+           diag::note_previous_decl)
+        << "exception specification";
+  }
+
+  D->addAttr(::new (S.Context) NoThrowAttr(
+      attr.getRange(), S.Context, attr.getAttributeSpellingListIndex()));
+}
+
 static void handleNoCallerSavedRegsAttr(Sema &S, Decl *D,
                                         const AttributeList &Attr) {
   if (S.CheckNoCallerSavedRegsAttr(Attr))
@@ -6192,7 +6211,7 @@
     handleNoReturnAttr(S, D, Attr);
     break;
   case AttributeList::AT_NoThrow:
-    handleSimpleAttribute<NoThrowAttr>(S, D, Attr);
+    handleNoThrowAttr(S, D, Attr);
     break;
   case AttributeList::AT_CUDAShared:
     handleSharedAttr(S, D, Attr);
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -1407,6 +1407,10 @@
   "argument to noexcept specifier must be a constant expression">;
 def err_exception_spec_not_parsed : Error<
   "exception specification is not available until end of class definition">;
+def warn_nothrow_attr_disagrees_with_exception_specification
+    : ExtWarn<"Attribute nothrow ignored, it disagrees with language specified "
+              "exception specification">,
+      InGroup<IgnoredAttributes>;
 
 // C++ access checking
 def err_class_redeclared_with_different_access : Error<


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D38205.116428.patch
Type: text/x-patch
Size: 2726 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20170925/49ddebf9/attachment-0001.bin>