Stuart Cook
8a5c66efb9
THIR patterns: Replace `AscribeUserType` and `ExpandedConstant` wrappers with per-node data This PR removes the `AscribeUserType` and `ExpandedConstant` variants from `thir::PatKind`, and replaces them with an `Option<Box<PatExtra>>` field attached to every `thir::Pat`. ### Why remove these variants? Unlike other THIR pattern kinds, these variants are mere “wrappers” that exist to attach some additional information to an underlying pattern node. There are several places where code that consumes THIR patterns needs to carefully “unpeel” any wrapper nodes, in order to match on the underlying pattern. This is clunky, and easy to forget to do, especially since it's not always obvious where the wrapper nodes can and can't appear. Attaching the data to an optional per-node field makes it easier for consuming code to simply ignore the extra data when it is not relevant. (One downside is that it is now easier to accidentally ignore the extra data when it *is* relevant, but I think that's generally a favourable tradeoff.) ### Impact After this change, THIR pattern trees should be “logically identical” to the previous THIR pattern trees, in the sense that information that was carried by wrapper nodes should now be directly attached to the non-wrapper nodes that were being wrapped. Types and spans associated with THIR pattern nodes should (hopefully!) still be accurate. There should be no change to the output of THIR-based checks or MIR building.
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