Rollup merge of #133153 - maxcabrajac:flat_maps, r=petrochenkov

Add visits to nodes that already have flat_maps in ast::MutVisitor

This PR aims to add `visit_` methods for every node that has a `flat_map_` in MutVisitor, giving implementers free choice over overriding `flat_map` for 1-to-n conversions or `visit` for a 1-to-1.

There is one major problem: `flat_map_stmt`.
While all other default implementations of `flat_map`s are 1-to-1 conversion, as they either only call visits or a internal 1-to-many conversions are natural, `flat_map_stmt` doesn't follow this pattern.

`flat_map_stmt`'s default implementation is a 1-to-n conversion that panics if n > 1 (effectively being a 1-to-[0;1]). This means that it cannot be used as is for a default `visit_stmt`, which would be required to be a 1-to-1.

Implementing `visit_stmt` without runtime checks would require it to reach over a potential `flat_map_item` or `filter_map_expr` overrides and call for their `visit` counterparts directly.
Other than that, if we want to keep the behavior of `flat_map_stmt` it cannot call `visit_stmt` internally.

To me, it seems reasonable to make all default implementations 1-to-1 conversions and let implementers handle `visit_stmt` if they need it, but I don't know if calling `visit` directly when a 1-to-1 is required is ok or not.

related to #128974 & #127615

r? ``@petrochenkov``

1 files changed, 16 insertions, 8 deletions

diff --git a/compiler/rustc_ast/src/visit.rs b/compiler/rustc_ast/src/visit.rs
index c121e7711ee..0302c9fa7f8 100644
--- a/compiler/rustc_ast/src/visit.rs
+++ b/compiler/rustc_ast/src/visit.rs
@@ -463,13 +463,6 @@ impl WalkItemKind for ItemKind {
     }
 }
 
-pub fn walk_item<'a, V: Visitor<'a>>(
-    visitor: &mut V,
-    item: &'a Item<impl WalkItemKind<Ctxt = ()>>,
-) -> V::Result {
-    walk_assoc_item(visitor, item, ())
-}
-
 pub fn walk_enum_def<'a, V: Visitor<'a>>(
     visitor: &mut V,
     EnumDef { variants }: &'a EnumDef,
@@ -931,7 +924,22 @@ impl WalkItemKind for AssocItemKind {
     }
 }
 
-pub fn walk_assoc_item<'a, V: Visitor<'a>, K: WalkItemKind>(
+pub fn walk_item<'a, V: Visitor<'a>>(
+    visitor: &mut V,
+    item: &'a Item<impl WalkItemKind<Ctxt = ()>>,
+) -> V::Result {
+    walk_item_ctxt(visitor, item, ())
+}
+
+pub fn walk_assoc_item<'a, V: Visitor<'a>>(
+    visitor: &mut V,
+    item: &'a AssocItem,
+    ctxt: AssocCtxt,
+) -> V::Result {
+    walk_item_ctxt(visitor, item, ctxt)
+}
+
+fn walk_item_ctxt<'a, V: Visitor<'a>, K: WalkItemKind>(
     visitor: &mut V,
     item: &'a Item<K>,
     ctxt: K::Ctxt,