https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119497
Arthur O'Dwyer <arthur.j.odwyer at gmail dot com> changed:
What |Removed |Added
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CC| |arthur.j.odwyer at gmail dot
com
--- Comment #6 from Arthur O'Dwyer <arthur.j.odwyer at gmail dot com> ---
Here's a proposed behavior for Clang (as I implemented in my Clang fork
yesterday).
<source>:30:15: error: constexpr variable 'val' must be initialized by a
constant expression
30 | constexpr int val = square(2);
| ^ ~~~~~~~~~
<source>:26:3: note: assertion failed during constant evaluation
26 | assert(result == 42); // expected-note {{assertion failed during
constant evaluation}}
| ^
<source>:11:24: note: expanded from macro 'assert'
11 | ((cond) ? (void)0 : __assert_fail(#cond, __FILE__, __LINE__,
__func__))
| ^
<source>:30:21: note: in call to 'square(2)'
30 | constexpr int val = square(2);
| ^~~~~~~~~
Points to note:
- I think "assertion failed during constant evaluation" is the clearest English
wording.
- With a static_assert, there can be a "message" attached. But C's assert(x)
cannot have a message: the "message" printed at runtime is always just the
stringification of #x, which is invariably visible to the end-user on the very
next line of GCC's output. So you needn't (and IMNSHO shouldn't) repeat that
string in the "assertion failed" message.
- The stringification of #x is not always the first argument; different
platforms put it in different positions (and Microsoft makes it a wchar_t
string literal). That's another reason not to try to repeat the stringification
of #x in GCC's compiler output.
- I'm ambivalent about whether the following note about "expanded from macro
assert" should be silenced or not. In Clang's case I think it was actually
difficult to silence, but even supposing we *could* silence it, *should* we? or
is it potentially useful?
- It would be *VERY* cool if the top-level error was not "constexpr variable
'val' must be initialized by a constant expression" but instead skipped
straight to the good part, e.g. "error: assertion failed during evaluation of
this constant expression". In C++26, you'll also want to do something like that
for an uncaught `throw` during constant evaluation. But that, also, seems
difficult in Clang.
@jwakely is correct that on OSX/Darwin the macro is named `__assert_rtn`.
