Rollup merge of #74960 - nbdd0121:typeck, r=nikomatsakis

Fix regionck failure when converting Index to IndexMut

Fixes #74933

Consider an overloaded index expression `base[index]`. Without knowing whether it will be mutated, this will initially be desugared into `<U as Index<T>>::index(&base, index)` for some `U` and `T`. Let `V` be the `expr_ty_adjusted` of `index`.

If this expression ends up being used in any mutable context (or used in a function call with `&mut self` receiver before #72280), we will need to fix it up. The current code will rewrite it to `<U as IndexMut<V>>::index_mut(&mut base, index)`. In most cases this is fine as `V` will be equal to `T`, however this is not always true when `V/T` are references, as they may have different region.

This issue is quite subtle before #72280 as this code path is only used to fixup function receivers, but after #72280 we've made this a common path.

The solution is basically just rewrite it to `<U as IndexMut<T>>::index_mut(&mut base, index)`. `T` can retrieved in the fixup path using `node_substs`.

0 files changed, 0 insertions, 0 deletions