r258110 - Fix PR26134: When substituting into default template arguments, keep CurContext unchanged.

[Hans Wennborg via cfe-commits]

It seems Richard is out of office, but perhaps he can verify this later.

Dimitry: go ahead and merge it (or let me know if you'd like me to).

On Fri, Jan 22, 2016 at 12:38 PM, Dimitry Andric <dimitry at andric.com> wrote:
> Hans,
>
> This change looks pretty trivial, and is required to not crash for the test cases in PR26134.  Can we merge it to release_38, please?
>
> -Dimitry
>
>> On 19 Jan 2016, at 19:28, Dimitry Andric via cfe-commits <cfe-commits at lists.llvm.org> wrote:
>>
>> Hi Richard,
>>
>> I am unsure if you are specifically the code owner of Sema, but can you please approve this change for the 3.8 branch?
>>
>> -Dimitry
>>
>>> On 19 Jan 2016, at 04:58, Faisal Vali via cfe-commits <cfe-commits at lists.llvm.org> wrote:
>>>
>>> Author: faisalv
>>> Date: Mon Jan 18 21:58:55 2016
>>> New Revision: 258110
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=258110&view=rev
>>> Log:
>>> Fix PR26134: When substituting into default template arguments, keep CurContext unchanged.
>>>
>>> Or, do not set Sema's CurContext to the template declaration's when substituting into default template arguments of said template declaration.
>>> If we do push the template declaration context on to Sema, and the template declaration is at namespace scope, Sema can get confused and try and do odr analysis when substituting into default template arguments, even though the substitution could be occurring within a dependent context.
>>> I'm not sure why this was being done, perhaps there was concern that if a default template argument referred to a previous template parameter, it might not be found during substitution - but all regression tests pass, and I can't craft a test that would cause it to fails (if some one does, please inform me, and i'll craft a different fix for the PR).
>>>
>>>
>>> This patch removes a single line of code, but unfortunately adds more than it removes, because of the tests.  Some day I still hope to commit a patch that removes far more lines than it adds, while leaving clang better for it ;)
>>>
>>> Sorry that r253590 ("Change the expression evaluation context from Unevaluated to ConstantEvaluated while substituting into non-type template argument defaults") caused the PR!
>>>
>>>
>>>
>>>
>>>
>>> Modified:
>>>   cfe/trunk/lib/Sema/SemaTemplate.cpp
>>>   cfe/trunk/test/SemaTemplate/default-arguments.cpp
>>>
>>> Modified: cfe/trunk/lib/Sema/SemaTemplate.cpp
>>> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaTemplate.cpp?rev=258110&r1=258109&r2=258110&view=diff
>>> ==============================================================================
>>> --- cfe/trunk/lib/Sema/SemaTemplate.cpp (original)
>>> +++ cfe/trunk/lib/Sema/SemaTemplate.cpp Mon Jan 18 21:58:55 2016
>>> @@ -3281,7 +3281,6 @@ SubstDefaultTemplateArgument(Sema &SemaR
>>>  for (unsigned i = 0, e = Param->getDepth(); i != e; ++i)
>>>    TemplateArgLists.addOuterTemplateArguments(None);
>>>
>>> -  Sema::ContextRAII SavedContext(SemaRef, Template->getDeclContext());
>>>  EnterExpressionEvaluationContext ConstantEvaluated(SemaRef,
>>>                                                     Sema::ConstantEvaluated);
>>>  return SemaRef.SubstExpr(Param->getDefaultArgument(), TemplateArgLists);
>>>
>>> Modified: cfe/trunk/test/SemaTemplate/default-arguments.cpp
>>> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaTemplate/default-arguments.cpp?rev=258110&r1=258109&r2=258110&view=diff
>>> ==============================================================================
>>> --- cfe/trunk/test/SemaTemplate/default-arguments.cpp (original)
>>> +++ cfe/trunk/test/SemaTemplate/default-arguments.cpp Mon Jan 18 21:58:55 2016
>>> @@ -179,3 +179,31 @@ struct C {
>>>  C(T t = ); // expected-error {{expected expression}}
>>> };
>>> C<int> obj;
>>> +
>>> +namespace PR26134 {
>>> +// Make sure when substituting default template arguments we do it in the current context.
>>> +template<class T, bool Val = T::value>
>>> +struct X {};
>>> +
>>> +template<bool B> struct Y {
>>> +  void f() { X<Y> xy; }
>>> +  static const bool value = B;
>>> +};
>>> +
>>> +namespace ns1 {
>>> +template<class T0>
>>> +struct X {
>>> +  template<bool B = T0::value> struct XInner { static const bool value = B; };
>>> +};
>>> +template<bool B> struct S { static const bool value = B; };
>>> +#if __cplusplus > 199711L
>>> +template<bool B> struct Y {
>>> +  static constexpr bool f() { return typename X<S<B>>::template XInner<>{}.value; }
>>> +  static_assert(f() == B, "");
>>> +};
>>> +Y<true> y;
>>> +Y<false> y2;
>>> +#endif
>>> +
>>> +} // end ns1
>>> +} // end ns PR26134
>>>
>>>
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