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[NFC] Change the evaluation context of a non-type default template argument from Unevaluated to ConstantEvaluated.

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This patch emits a more appropriate (but still noisy) diagnostic stream when a lambda-expression is encountered within a non-type default argument. 

For e.g. template<int N = ([] { return 5; }())> int f();

As opposed to complaining that a lambda expression is not allowed in an unevaluated operand, the patch complains about the lambda being forbidden in a constant expression context (which will be allowed in C++17 now that they have been accepted by EWG, unless of course CWG or national bodies (that have so far shown no signs of concern) rise in protest) 

As I start submitting patches for constexpr lambdas (http://wg21.link/P0170R0) under C++1z (OK'd by Richard Smith at Kona), this will be one less change to make.

Thanks!

llvm-svn: 253431
This commit is contained in:
Faisal Vali 2015-11-18 04:29:22 +00:00
parent 8447ff6357
commit 0374bf0d07
2 changed files with 16 additions and 1 deletions
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3
clang/lib/Parse/ParseTemplate.cpp
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@ -695,7 +695,8 @@ Parser::ParseNonTypeTemplateParameter(unsigned Depth, unsigned Position) {
// end of the template-parameter-list rather than a greater-than
// operator.
GreaterThanIsOperatorScope G(GreaterThanIsOperator, false);
EnterExpressionEvaluationContext Unevaluated(Actions, Sema::Unevaluated);
EnterExpressionEvaluationContext Unevaluated(Actions,
Sema::ConstantEvaluated);
DefaultArg = Actions.CorrectDelayedTyposInExpr(ParseAssignmentExpression());
if (DefaultArg.isInvalid())

14
clang/test/CXX/temp/temp.arg/temp.arg.nontype/p1.cpp
View File

@ -1,4 +1,5 @@
// RUN: %clang_cc1 -fsyntax-only -verify -triple=x86_64-linux-gnu %s
// RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify -triple=x86_64-linux-gnu %s -DCPP11ONLY
// C++11 [temp.arg.nontype]p1:
//
@ -6,6 +7,8 @@
// be one of:
// -- an integral constant expression; or
// -- the name of a non-type template-parameter ; or
#ifndef CPP11ONLY
namespace non_type_tmpl_param {
template <int N> struct X0 { X0(); };
template <int N> X0<N>::X0() { }
@ -95,3 +98,14 @@ namespace bad_args {
int* iptr = &i;
X0<iptr> x0b; // expected-error{{non-type template argument for template parameter of pointer type 'int *' must have its address taken}}
}
#endif // CPP11ONLY
namespace default_args {
#ifdef CPP11ONLY
namespace lambdas {
template<int I = ([] { return 5; }())> //expected-error 2{{constant expression}} expected-note{{constant expression}}
int f();
}
#endif // CPP11ONLY
}