On Tue, Aug 14, 2018 at 11:51 PM Elijah Newren <newren@xxxxxxxxx> wrote: > > [...] > > >> enums are of unknown size, so forward declarations don't work for > > >> them. See bb/pedantic for some examples. > > > > > > structs are also of unknown size; the size is irrelevant when the > > > function signature merely uses a pointer to the struct or enum. The > > > enum forward declaration fixes a compilation bug. > > > > My rationale may miss the point but the standard and some real compilers > > don't like this, unfortunately. > > > > For structs, having an incomplete type is fine, but for enums we need > > the full definition. E.g. C99 sayeth (in section 6.7.2.3 "tags") > > > > A type specifier of the form > > > > enum identifier > > > > without an enumerator list shall only appear after the type it > > specifies is complete. > > What about a type specifier of the form > enum identifier * > ? Can that kind of type specifier appear before the full definition > of the enum? (Or, alternatively, if the standard doesn't say, are > there any compilers that have a problem with that?) > > If so, we can include cache.h instead. We'll probably also have to > fix up packfile.h for the exact same issue (even the same enum name) > if that's the case. Digging a little further this morning, apparently C++ has defined a forward declaration of an enum to either be useless (because it was already defined), require an explicit size specifier, or be a compilation error. That seemed stupid to me, but a little more digging turned up http://c-faq.com/null/machexamp.html , which states that sizeof(char*) != sizeof(int*) on some platforms. That was a big surprise to me. Since an enum could be a char or int (or long or...), knowing the size of the enum thus is important to knowing the size of a pointer to an enum, so we actually do need the full enum definition (or a C++ style explicit size specifier). What a crazy world. So, I'll go with the inclusion of cache.h and also fix up packfile.h the same way. Thanks for pointing this out, Jonathan.
