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Non-derive proc 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 before expansion. 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 is the same approach as commit 3445a65 ("internal: rework how `#[pin_data]` handles cfg"). Signed-off-by: Gary Guo <gary@garyguo.net>
Add a test with 26 cfg options to test linear time behaviour of cfg resolution. If the cfg-expansion approach is exponential, this test will cause a timeout. Signed-off-by: Gary Guo <gary@garyguo.net>
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Non-derive proc 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 before expansion.
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 is the same approach as #161 but for init macros. This should hopefully also help #155 by removing the cfg limitation.