https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92193
Bug ID: 92193
Summary: Poor diagnostics when a constexpr function call
follows a failed static_assert
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Keywords: diagnostic
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
CC: jason at gcc dot gnu.org
Target Milestone: ---
If we compile this with NO_CONSTEXPR the diagnostic is fine:
template<typename T>
struct has_foo
{ static constexpr bool value = false; };
template<typename T>
#ifndef NO_CONSTEXPR
constexpr
#endif
bool
foo(T t) noexcept(noexcept(t.foo()))
{ return t.foo(); }
template<typename T>
void
maybe_foo(T t)
{
static_assert( has_foo<T>::value, "has foo" );
foo(t);
}
struct X { };
int main()
{
X x;
maybe_foo(x);
}
ce.cc: In instantiation of ‘void maybe_foo(T) [with T = X]’:
ce.cc:26:14: required from here
ce.cc:17:20: error: static assertion failed: has foo
static_assert( has_foo<T>::value, "has foo" );
^~~~~~~~~~
However, when the function is constexpr the output is much worse:
ce.cc: In instantiation of ‘void maybe_foo(T) [with T = X]’:
ce.cc:23:14: required from here
ce.cc:14:20: error: static assertion failed: has foo
static_assert( has_foo<T>::value, "has foo" );
^~~~~~~~~~
ce.cc: In instantiation of ‘constexpr bool foo(T) [with T = X]’:
ce.cc:15:8: required from ‘void maybe_foo(T) [with T = X]’
ce.cc:23:14: required from here
ce.cc:7:32: error: ‘struct X’ has no member named ‘foo’
foo(T t) noexcept(noexcept(t.foo()))
~~^~~
ce.cc: In instantiation of ‘constexpr bool foo(T) [with T = X]’:
ce.cc:15:8: required from ‘void maybe_foo(T) [with T = X]’
ce.cc:23:14: required from here
ce.cc:7:32: error: ‘struct X’ has no member named ‘foo’
ce.cc:8:14: error: ‘struct X’ has no member named ‘foo’
{ return t.foo(); }
~~^~~
The errors following the static assertion are not useful. The static_assert is
there precisely to make compilation fail, but it doesn't stop errors being
produced from the constexpr function that follows it (even though we're in a
non-constexpr function).
This affects libstdc++ because adding 'constexpr' throughout the library means
that suddenly we get loads more errors in the testsuite and need to tell
dejagnu to ignore them.
