On Mon, Dec 02, 2019 at 07:55:45AM -0800, Andres Freund wrote: > On 2019-11-29 11:11:25 +0900, Michael Paquier wrote: >> diff --git a/src/include/c.h b/src/include/c.h >> index 00e41ac546..91d6d50e76 100644 >> --- a/src/include/c.h >> +++ b/src/include/c.h >> [...] > > I think this a) needs an updated comment above, explaining this approach > (note the explanation for the array approach) b) I still think we ought > to work towards also using this implementation for StaticAssertStmt.
Sure. I was not completely sure which addition would be helpful
except than adding in the main comment lock that Decl() is useful at
file scope.
> Now that I'm back from vacation, I'll try to take a stab at b). It
> should definitely doable to use the same approach for StaticAssertStmt,
> the problematic case might be StaticAssertExpr.
So you basically want to minimize the amount of code relying on
external compiler expressions? Sounds like a plan. At quick glance,
it seems that this should work. I haven't tested though. I'll wait
for what you come up with then.
>> #else /* C++ */
>> #if defined(__cpp_static_assert) && __cpp_static_assert >= 200410
>> @@ -857,12 +862,16 @@ extern void ExceptionalCondition(const char
>> *conditionName,
>> static_assert(condition, errmessage)
>> #define StaticAssertExpr(condition, errmessage) \
>> ({ static_assert(condition, errmessage); })
>>
>> [...]
>>
>> +#define StaticAssertDecl(condition, errmessage) \
>> + extern void static_assert_func(int static_assert_failure[(condition) ?
>> 1 : -1])
>> +#endif /*
>> __cpp_static_assert */
>> #endif /* C++ */
>
> I wonder if it's worth moving the fallback implementation into an else
> branch that's "unified" between C and C++.
I suspect that you would run into problems with StaticAssertExpr() and
StaticAssertStmt().
>> +StaticAssertDecl(lengthof(LockTagTypeNames) == (LOCKTAG_ADVISORY + 1),
>> + "LockTagTypeNames array inconsistency");
>> +
>
> These error messages strike me as somewhat unhelpful. I'd probably just
> reword them as "array length mismatch" or something like that.
That's indeed better. Now I think that it is useful to have the
structure name in the error message as well, no?
> I think this patch ought to include at least one StaticAssertDecl in a
> header, to make sure we get that part right across compilers. E.g. the
> one in PageIsVerified()?
No objections to have one, but I don't think that your suggestion is a
good choice. This static assertion is based on size_t and BLCKSZ, and
is located close to a code path where we have a specific logic based
on both things. If in the future this code gets removed, then we'd
likely miss to remove the static assertion if they are separated
across multiple files.
--
Michael
signature.asc
Description: PGP signature
