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From: "potswa at mac dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/52809] New: Template non-dependent static_assert diagnostics may confuse
Date: Sat, 31 Mar 2012 16:55:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D52809

             Bug #: 52809
           Summary: Template non-dependent static_assert diagnostics may
                    confuse
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: potswa@mac.com


A static_assert declaration that does not depend on template parameters wil=
l be
detected and reported while parsing the template, before any instantiation.
This is OK because such a template would have no valid instantiation, which
immediately renders the program ill-formed.

In terms of cosmetic QOI, however, it would be better to clarify the messag=
es
for users who don't know all the rules. Intuitively, the assertion shouldn'=
t be
evaluated until instantiation, regardless of dependence. The user might exp=
ect
an uninstantiated template to pass through. We should add something like
"error: template MyTemplate cannot have a valid instantiation" after the
static_assert diagnostic.

Example code and result, as currently implemented:

template< bool b >
struct s {
    static_assert( b, "uhoh" );
    static_assert( false, "yikes" );
};

s< false > q;

depassert.cpp:4:1: error: static assertion failed: yikes
depassert.cpp: In instantiation of =E2=80=98struct s<false>=E2=80=99:
depassert.cpp:7:12:   required from here
depassert.cpp:3:1: error: static assertion failed: uhoh