commit 5f588570b487edf8e720571a65834019478bb104
author bors <bors@rust-lang.org> Sun Jun 22 14:03:44 2025 +0000
committer bors <bors@rust-lang.org> Sun Jun 22 14:03:44 2025 +0000
tree ad9938a39f24f9319b0026d34e756c53cf87c967
parent 89a89dfb170e461270c75b7535ac7c4670ddede5
parent a11b90f86b3329925e715a9e3f0fbe2320870332

Auto merge of #142706 - fee1-dead-contrib:push-zsznlqyrzsqo, r=oli-obk

completely deduplicate `Visitor` and `MutVisitor`

r? oli-obk

This closes rust-lang/rust#127615.

### Discussion

> * Give every `MutVisitor::visit_*` method a corresponding `flat_map_*` method.

Not every AST node exists in a location where they can be mapped to multiple instances of themselves. Not every AST node exists in a location where they can be removed from existence (e.g. `filter_map_expr`). I don't think this is doable.

> * Give every `MutVisitor::visit_*` method a corresponding `Visitor` method and vice versa

The only three remaining method-level asymmetries after this PR are `visit_stmt` and `visit_nested_use_tree` (only on `Visitor`) and `visit_span` (only on `MutVisitor`).

`visit_stmt` doesn't seem applicable to `MutVisitor` because `walk_flat_map_stmt_kind` will ask `flat_map_item` / `filter_map_expr` to potentially turn a single `Stmt` to multiple based on what a visitor wants. So only using `flat_map_stmt` seems appropriate.

`visit_nested_use_tree` is used for `rustc_resolve` to track stuff. Not useful for `MutVisitor` for now.

`visit_span` is currently not used for `MutVisitor` already, it was just kept in case we want to revive rust-lang/rust#127241. cc `@cjgillot` maybe we could remove for now and re-insert later if we find a use-case? It does involve some extra effort to maintain.

* Remaining FIXMEs

`visit_lifetime` has an extra param for `Visitor` that's not in `MutVisitor`. This is again something only used by `rustc_resolve`. I think we can keep that symmetry for now.