Pre-compute LocalDefId <-> HirId mappings and remove NodeId <-> HirId conversion APIs

[marmeladema]

cc #50928

I don't know who is exactly the best person to review this.

r? @petrochenkov

[marmeladema]

Next step is probably to move

 node_id_to_def_id:FxHashMap<ast::NodeId,LocalDefId>,
def_id_to_node_id:IndexVec<LocalDefId, ast::NodeId>,

mappings from hir::Definitions to Resolver such that any references to NodeId are gone with it.

[petrochenkov]

What is the end goal here, removing any mentions of NodeId from struct Definitions?

Definitions is a pretty heterogeneous structure.
Perhaps it can be split into two structures instead, one for fields used before lowering to HIR, and one for fields used after lowering to HIR?

structDefinitions{// Both before and after (or filled before, used after)table:DefPathTable,parent_modules_of_macro_defs:FxHashMap<ExpnId,DefId>,expansions_that_defined:FxHashMap<LocalDefId,ExpnId>,// Beforedef_id_to_span:IndexVec<LocalDefId,Span>,node_id_to_def_id:FxHashMap<ast::NodeId,LocalDefId>,def_id_to_node_id:IndexVec<LocalDefId, ast::NodeId>,next_disambiguator:FxHashMap<(LocalDefId,DefPathData),u32>,invocation_parents:FxHashMap<ExpnId,LocalDefId>,placeholder_field_indices:FxHashMap<ast::NodeId,usize>,// ???node_id_to_hir_id:IndexVec<ast::NodeId,Option<hir::HirId>>,hir_id_to_node_id:FxHashMap<hir::HirId, ast::NodeId>,}

Having the "before" fields in the ResolverOutputs version of Definitions doesn't make any sense, but they are currently placed there.

[petrochenkov]

The "after" fields could actually go into ResolverOutputs directly, without any additional structure.
So Definitions will exist solely during early compilation as a part of Resolver.

[marmeladema]

My idea was to move everything NodeId related (ie: the "before" fields) into the Resolver such that they are dropped with it but I would keep the rest of the fields in Definitions.

So to summarize, using this PR as base of discussion, Definitions would only contains:

• def_id_to_hir_id
• hir_id_to_def_id
• table
• parent_modules_of_macro_defs
• expansions_that_defined
  which is the list of fields that should be available post HIR lowering.

TL;DR: "before" fields in Resolver, "after" fields kept in Definitions.

[petrochenkov]

@marmeladema

TL;DR: "before" fields in Resolver, "after" fields kept in Definitions.

Sounds like a plan!

[petrochenkov]

ID memo:

• LocalDefId - the best variant, if you can use it for something do it. Cannot address entities in other crates and fine-grained entities like individual expressions in the current crate. Can address any items.
• DefId - the second choice. Can address entities in other crates, but cannot address fine-grained entities like individual expressions.
• HirId - Can address fine-grained entities like individual expressions in the current crate. Fine-grained entities from other crates can never be addressed in rustc.
• NodeId - The last choice. Can address fine-grained entities like individual expressions when HirIds are not yet created.

cc @mark-i-m this can probably be added to the dev guide

[bors]

☔ The latest upstream changes (presumably #73511) made this pull request unmergeable. Please resolve the merge conflicts.

[petrochenkov]

#73357 has landed.

[marmeladema]

@petrochenkov rebased and fixed the conflicts 👍

[petrochenkov]

@bors r+

[bors]

📌 Commit 13104ef has been approved by petrochenkov