https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93414
Bug ID: 93414
Summary: Bad diagnostics for dynamic_cast during constant
evaluation: implementation details leak out
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Keywords: diagnostic
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: antoshkka at gmail dot com
Target Milestone: ---
Consider the example that attempts to throw a std::bad_cast:
struct Base {
constexpr virtual ~Base(){}
};
struct Derived: Base {
constexpr ~Derived(){}
};
constexpr const Derived& cast(const Base& b) {
return dynamic_cast<const Derived&>(b); // error!
}
auto test() {
static constexpr Base b;
constexpr auto res = cast(b);
return res;
}
The error message is following:
<source>: In function 'constexpr const Derived& cast(const Base&)':
<source>:10:42: error: call to non-'constexpr' function 'void*
__cxa_bad_cast()'
10 | return dynamic_cast<const Derived&>(b); // error: call to
non-'constexpr' function 'void* __cxa_bad_cast()'
That's not informative: users usually know nothing about __cxa_bad_cast
Please change the error message to something more informative, for example
"During constexpr evaluation attempt to cast a variable `b` with typeid(b) ==
typeid(Base) to `Derived` was detected"
