Module hir_expand::eager
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Eager expansion related utils
Here is a dump of a discussion from Vadim Petrochenkov about Eager Expansion and Its name resolution :
Eagerly expanded macros (and also macros eagerly expanded by eagerly expanded macros, which actually happens in practice too!) are resolved at the location of the “root” macro that performs the eager expansion on its arguments. If some name cannot be resolved at the eager expansion time it’s considered unresolved, even if becomes available later (e.g. from a glob import or other macro).
Eagerly expanded macros don’t add anything to the module structure of the crate and don’t build any speculative module structures, i.e. they are expanded in a “flat” way even if tokens in them look like modules.
In other words, it kinda works for simple cases for which it was originally intended, and we need to live with it because it’s available on stable and widely relied upon.
See the full discussion : https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/Eager.20expansion.20of.20built-in.20macros