Auto merge of #10853 - MarcusGrass:fix-from-over-into-self, r=Alexendoo

Ignore fix for `from_over_into` if the target type contains a `Self` reference

Fixes rust-lang/rust-clippy#10838.

This is my first time contributing here, and the fix is kind of ugly.
I've worked a bit with `quote` and was trying to figure out a way to replace the type in a better way than just a raw string-replace but couldn't quite figure out how to.

The only thing really required to fix this, is to replace all `Self` references with the type stated in the `from` variable, this isn't entirely simple to do with raw strings without creating a mess though.

We need to find and replace all `Self`'s in a variable with `from` but there could be an arbitrary amount, in a lot of different positions. As well as some type that contains the name self, like `SelfVarSelf` which shouldn't be replaced.

The strategy is essentially, if `"Self"` is surrounded on both sides by something that isn't alphanumeric, then we're golden, then trying to make that reasonably efficient.

I would not be offended if the solution is too messy to accept!

changelog: [from_over_into]: Replace Self with the indicated variable in suggestion and fix.

Author: bors

clippy_lints/src/from_over_into.rs

@@ -156,6 +156,11 @@ fn convert_to_from(
     self_ty: &Ty<'_>,
     impl_item_ref: &ImplItemRef,
 ) -> Option<Vec<(Span, String)>> {
+    if !target_ty.find_self_aliases().is_empty() {
+        // It's tricky to expand self-aliases correctly, we'll ignore it to not cause a
+        // bad suggestion/fix.
+        return None;
+    }
     let impl_item = cx.tcx.hir().impl_item(impl_item_ref.id);
     let ImplItemKind::Fn(ref sig, body_id) = impl_item.kind else { return None };
     let body = cx.tcx.hir().body(body_id);

tests/ui/from_over_into_unfixable.rs

@@ -32,4 +32,14 @@ impl Into<u8> for ContainsVal {
     }
 }
 
+pub struct Lval<T>(T);
+
+pub struct Rval<T>(T);
+
+impl<T> Into<Rval<Self>> for Lval<T> {
+    fn into(self) -> Rval<Self> {
+        Rval(self)
+    }
+}
+
 fn main() {}

tests/ui/from_over_into_unfixable.stderr

@@ -25,5 +25,13 @@ LL | impl Into<u8> for ContainsVal {
            https://doc.rust-lang.org/reference/items/implementations.html#trait-implementation-coherence
    = help: replace the `Into` implementation with `From<ContainsVal>`
 
-error: aborting due to 3 previous errors
+error: an implementation of `From` is preferred since it gives you `Into<_>` for free where the reverse isn't true
+  --> $DIR/from_over_into_unfixable.rs:39:1
+   |
+LL | impl<T> Into<Rval<Self>> for Lval<T> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: replace the `Into` implementation with `From<Lval<T>>`
+
+error: aborting due to 4 previous errors