tree a98001ba0a2082bc7261ab807217b4b8a382bf3b
parent efd635d1642fc2a29e11988d28bff7372f4595a4
author Lukasz Anforowicz <lukasza@google.com> 1663870003 -0700
committer Copybara-Service <copybara-worker@google.com> 1663870033 -0700

Delete `RcEq<T>` and instead provide `impl PartialEq for RsSnippet`.

`salsa` requires that all query keys and query results can be compared
for equality.  Key equality is needed for basic `salsa` functionality
(memoization of previous computations).  Result equality is needed to
determine that a changed input doesn't affect the result of a given
computation (and therefore computations transitively depending on the
result don't need to be redone).

Before this CL, equality of some query results was provided by `RcEq<T>`
in Crubit's `salsa_utils.rs` (inspired by Chalk's `ArcEq`).  This worked
but pointer-based-equality would unnecessary treat equivalent results as
different.  This doesn't matter in practice, because Crubit never
resets `salsa` inputs (i.e. only calls `set_ir` once) and so `salsa`
would never need to check equality of `RcEq`.  Still, having real,
non-pointer-based equality should help with incremental computations
in the future (if they ever become used by Crubit).  And deleting
`salsa_utils.rs` also means the code is smaller and easier to
understand.

PiperOrigin-RevId: 476146950