On Tue, 11 Aug 2020, Richard Smith wrote:
On Tue, 11 Aug 2020 at 00:29, Martin Storsjö <mar...@martin.st> wrote: On Sun, 9 Aug 2020, Richard Smith via cfe-commits wrote:> > Author: Richard Smith > Date: 2020-08-09T23:22:26-07:00 > New Revision: 617007240cbfb97c8ccf6d61b0c4ca0bb62d43c9 > > URL:https://github.com/llvm/llvm-project/commit/617007240cbfb97c8ccf6d61b0c4ca0 bb62d43c9 > DIFF:https://github.com/llvm/llvm-project/commit/617007240cbfb97c8ccf6d61b0c4ca0 bb62d43c9.diff > > LOG: Improve modeling of variable template specializations with dependent > arguments. > > Don't build a variable template specialization declaration until its > scope and template arguments are non-dependent. > > No functionality change intended, but the AST representation is now more > consistent with how we model other templates. This did turn out to make a functional change, breaking building the dev branch of Qt. A halfway reduced example below: Thanks for reporting this! Reduced a bit more: template<class _Tp, class _Arg> inline constexpr bool is_nothrow_assignable_v = true; template<class T> class QCache { void replace() noexcept(is_nothrow_assignable_v<T>); }; We used to allow this and now reject. This code is ill-formed (no diagnostic required) by [temp.res]/8, because it has no valid instantiations, because the second template argument of is_nothrow_assignable_v is missing. So, assuming the case from which this was reduced was similarly ill-formed (which it looks like itis: https://github.com/qt/qtbase/blob/48c8322a613f58d19ad9e0262bbac437ce259 8f8/src/corelib/tools/qcache.h#L114), I think that's a (minor) quality of implementation improvement -- we now diagnose a bug that we used to miss. ICC also rejects this, although GCC does not, and all three compilers reject the corresponding case using a class template instead of a variable template.
Thanks! I sent an attempt at a fix upstream at https://codereview.qt-project.org/c/qt/qtbase/+/309878.
// Martin
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