Add Documentation to attribute-nothrow. Additionally, limit to functions.

[erichkeane]

Summary

Attribute nothrow is only allowed on functions, so I added that. Additionally,
it lacks any documentation, so I added some. Please wordsmith!

[aaron.ballman]

include/clang/Basic/AttrDocs.td

2692 ↗

(On Diff #116424)

Should probably add something about __declspec(nothrow) as well.

Are the semantics really identical to noexcept? For instance, does std::terminate() get called if a function is marked __declspec(nothrow) and it throws, or does it simply crash?

2694 ↗

(On Diff #116424)

"does cannot"

[erichkeane]

include/clang/Basic/AttrDocs.td

2692 ↗

(On Diff #116424)

I'm unable in GCC to identify any difference between nothrow and noexcept. It DOES do std::terminate in 7.2, and presumably older versions as well.

[erichkeane]

Added declspec, fixed does cannot.

[aaron.ballman]

LGTM!

cfe/trunk/include/clang/Basic/Attr.td

 def NotTailCalled : InheritableAttr {
   let Spellings = [GNU<"not_tail_called">, CXX11<"clang", "not_tail_called">];
   let Subjects = SubjectList<[Function]>;
   let Documentation = [NotTailCalledDocs];
 }
 
 def NoThrow : InheritableAttr {
   let Spellings = [GCC<"nothrow">, Declspec<"nothrow">];
-  let Documentation = [Undocumented];
+  let Subjects = SubjectList<[Function]>;
+  let Documentation = [NoThrowDocs];
 }
 
 def NvWeak : IgnoredAttr {
   // No Declspec spelling of this attribute; the CUDA headers use
   // __attribute__((nv_weak)) unconditionally.
   let Spellings = [GNU<"nv_weak">];
   let LangOpts = [CUDA];
 }

cfe/trunk/include/clang/Basic/AttrDocs.td

public:
       int foo1() override;
 
       // not_tail_called on a virtual function is an error.
       [[clang::not_tail_called]] int foo2() override;
     };
   }];
 }
 
+def NoThrowDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+Clang supports the GNU style ``__attribute__((nothrow))`` and Microsoft style
+``__declspec(nothrow)`` attribute as an equivilent of `noexcept` on function
+declarations. This attribute informs the compiler that the annotated function
+does not throw an exception. This prevents exception-unwinding. This attribute
+is particularly useful on functions in the C Standard Library that are
+guaranteed to not throw an exception.
+    }];
+}
+
 def InternalLinkageDocs : Documentation {
   let Category = DocCatFunction;
   let Content = [{
 The ``internal_linkage`` attribute changes the linkage type of the declaration to internal.
 This is similar to C-style ``static``, but can be used on classes and class methods. When applied to a class definition,
 this attribute affects all methods and static data members of that class.
 This can be used to contain the ABI of a C++ library by excluding unwanted class methods from the export tables.
   }];

cfe/trunk/test/Misc/pragma-attribute-supported-attributes-list.test

 // CHECK-NEXT: MipsShortCall (SubjectMatchRule_function)
 // CHECK-NEXT: NoDebug (SubjectMatchRule_hasType_functionType, SubjectMatchRule_objc_method, SubjectMatchRule_variable_not_is_parameter)
 // CHECK-NEXT: NoDuplicate (SubjectMatchRule_function)
 // CHECK-NEXT: NoEscape (SubjectMatchRule_variable_is_parameter)
 // CHECK-NEXT: NoMicroMips (SubjectMatchRule_function)
 // CHECK-NEXT: NoSanitize (SubjectMatchRule_function, SubjectMatchRule_objc_method, SubjectMatchRule_variable_is_global)
 // CHECK-NEXT: NoSanitizeSpecific (SubjectMatchRule_function, SubjectMatchRule_variable_is_global)
 // CHECK-NEXT: NoSplitStack (SubjectMatchRule_function)
+// CHECK-NEXT: NoThrow (SubjectMatchRule_function)
 // CHECK-NEXT: NotTailCalled (SubjectMatchRule_function)
 // CHECK-NEXT: ObjCBoxable (SubjectMatchRule_record)
 // CHECK-NEXT: ObjCMethodFamily (SubjectMatchRule_objc_method)
 // CHECK-NEXT: ObjCRequiresSuper (SubjectMatchRule_objc_method)
 // CHECK-NEXT: ObjCRuntimeName (SubjectMatchRule_objc_interface, SubjectMatchRule_objc_protocol)
 // CHECK-NEXT: ObjCRuntimeVisible (SubjectMatchRule_objc_interface)
 // CHECK-NEXT: ObjCSubclassingRestricted (SubjectMatchRule_objc_interface)
 // CHECK-NEXT: OpenCLIntelReqdSubGroupSize (SubjectMatchRule_function)