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Attribute macros are invoked without cfg being resolved. This adds quite a bit complexity to the macro because all of the macro needs to be careful to attach necessary cfgs. This becomes especially tricky for tuple structs. Thus, it is convenient if cfgs are all resolved like derive macros. The most optimal way to handle this is via `TokenStream::expand_expr`, but that is still unstable. We can also create an internal derive macro and transform the attribute macro invocation to be derive macro, but doing requires us to serialize all extracted information in a form of helper attributes; it would also make it more difficult if we want to make changes to the struct (which the self-reference feature would need). Implement an approach where we generate two cfg-gated macro invocations with cfg resolved within the invocation. This would mean when the loop falls through, all field cfgs are resolved, so remove all handling of cfg_attrs for the rest of the macro. Signed-off-by: Gary Guo <gary@garyguo.net>
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I'm unhappy about the cfg handling in #155, and when working on self-referential pin-init the conditional existence of fields become annoying as well. So here's an alternative way of handling this.
cc @mqqz
Attribute macros are invoked without cfg being resolved. This adds quite a bit complexity to the macro because all of the macro needs to be careful to attach necessary cfgs. This becomes especially tricky for tuple structs. Thus, it is convenient if cfgs are all resolved like derive macros.
The most optimal way to handle this is via
TokenStream::expand_expr, but that is still unstable. Implement an approach where we generate two cfg-gated macro invocations with cfg resolved within the invocation. This would mean when the loop falls through, all field cfgs are resolved, so remove all handling of cfg_attrs for the rest of the macro.