I am actually trying to fix this unclear diagnostic in Clang. `assert` is
allowed in a constant expression by the spec (so long as the expression is
true), and the way most libcs fail an assert during constant evaluation is
by calling an implementation-defined function that is not a constant
expression (e.g. `__assert_fail`).

https://github.com/llvm/llvm-project/pull/130458

I'd welcome your input on that PR. I'm overloaded with schoolwork and can't
figure out why I broke a bunch of test cases.

On Wed, Mar 26, 2025 at 11:05 AM Robin Savonen Söderholm via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> Or you evaluate a non-constexpr expression inside the assert (there is a
> pointer derefencing happening there that could be the culprit if it points
> to something not constant evaluat-able).
>
> // Robin
>
> On Wed, Mar 26, 2025, 15:52 Jonathan Wakely via Std-Proposals <
> std-proposals_at_[hidden]> wrote:
>
>>
>>
>> On Wed, 26 Mar 2025 at 14:40, Frederick Virchanza Gotham via
>> Std-Proposals <std-proposals_at_[hidden]> wrote:
>>
>>> Today my compiler gave me the following output:
>>>
>>> md5.hpp:244:21: error: call to non-‘constexpr’ function ‘void
>>> __assert_fail(const char*, const char*, unsigned int, const char*)’
>>> 244 | assert( 0u == (*ptr >> 8u) );
>>>
>>>
>>> We should be able to use 'assert' in a constexpr function.
>>
>>
>> You can.
>>
>>
>>> If the
>>> function is invoked at compile time (instead of runtime), then it
>>> should be as if the 'assert' was never there. This would be the
>>> easiest way of doing it.
>>>
>>
>> I don't see why we'd want that.
>>
>>
>>>
>>> A more complicated way of doing it would be to get the compiler at
>>> compile time to actually evaluate the assertion, and to cease
>>> compiling if the assertion fails -- this would be ideal.
>>>
>>
>> Isn't that exactly what happened in this case?
>>
>> assert is already allowed in constexpr functions, there's only a problem
>> if the assertion fails. If that happens, it tries to call a non-constexpr
>> function and you get an error.
>>
>>
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>>
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