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I'm confused about a couple things:

* What is metadata_decode_entry_impl_trait_header and what does it have to do with proc macros? I suppose if a proc macro emitted code that used impl Trait a bunch then it might need to use this code, but I don't see why that would disproportionately affect compile times.

* What's the proposal for how to fix this?

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It's used to compile proc macros. in order to fix this typeck needs to not use them which is a huge rewrite alone.

In what specific sense is metadata_decode_entry_impl_trait_header "used to compile proc macros" and where did you find this information? And what does the article mean by "and finally it can be fixed"?

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