Mention sharing the solver with rust-analyzer

[ShoyuVanilla]

r? lcnr

[lcnr]

Thanks for writing this 😊

I think we should explain a few specific concepts here and would have separate headers for each of them:

• trait Interner already mostly done
  • I'd explicitly mention that it corresponds to the TyCtxt in rustc and is where we put rustc querys
• mod inherent
  • forward definitions of inherent methods on compiler specific types
  • should be imported via use inherent::*; in the generic crates
  • never used inside of the implementations themselves, they should use the inherent methods of the actual types once they are nameable
• trait InferCtxtLike and trait SolverDelegate
  • corresponds to the InferCtxt in rustc
  • InferCtxtLike has do be defined in rustc_infer due to coherence rules, does not provide functionality defined in rustc_trait_selection
  • that behavior is abstracted over via the separate SolverDelegate trait
  • ideally all of SolverDelegate should be extracted into the rustc_next_trait_solver with the necessary core operations added to InferCtxtLike
• rustc_type_ir::search_graph::{Cx, Delegate}
  • abstraction traits already implemented in rustc_next_trait_solver itself, used to support fuzzing of the search graph outside of the trait solver in https://github.com/lcnr/search_graph_fuzz, not relevant for users of the trait solver

[lcnr]

Suggested change

	## The Abstract Layer
	## The Abstraction Layer

I think? The layer is used to abstract something, it's not abstract itself

[lcnr]

Suggested change

	To bridge these differences, the compiler provides `rustc_type_ir` as an abstract layer shared
	To bridge these differences, the compiler provides `rustc_type_ir` as an abstraction layer shared

[lcnr]

Suggested change

	To support this, the type-system traits in `rustc_type_ir` must expose every interface the solver
	requires—for example, [creating a new inference type variable][ir new_infer]
	([rustc][rustc new_infer], [rust-analyzer][r-a new_infer])
	To support this, the type-system traits in `rustc_type_ir` must expose every interface the solver
	requires—for example, [creating a new inference type variable][ir new_infer]
	([rustc][rustc new_infer], [rust-analyzer][r-a new_infer]).

[ShoyuVanilla]

Thanks for the review! I'll apply your feedback some hours later 😄