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Add some details about `DefId` creation

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Oliver Schneider 2018-07-05 09:34:37 +02:00 committed by Who? Me?!
parent e54c0c413f
commit 3166fb9d3e
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src/lowering.md
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@ -32,4 +32,16 @@ sanity checks in `src/librustc/hir/map/hir_id_validator.rs`:
4. If you are creating new nodes that didn't exist in the `AST`, you *must* 4. If you are creating new nodes that didn't exist in the `AST`, you *must*
create new ids for them. This is done by calling the `next_id` method, create new ids for them. This is done by calling the `next_id` method,
which produces both a new `NodeId` as well as automatically lowering it which produces both a new `NodeId` as well as automatically lowering it
for you so you also get the `HirId`. for you so you also get the `HirId`.
If you are creating new `DefId`s, since each `DefId` needs to have a corresponding
`NodeId`, it is adviseable to add these `NodeId`s to the `AST` so you don't have
to generate new ones during lowering. This has the advantage of creating a
way to find the `DefId` of something via its `NodeId`. If lowering needs this
`DefId` in multiple places, you can't generate a new `NodeId` in all those places
because you'd also get a new `DefId` then. With a `NodeId` from the `AST` this is
not an issue.
Having the `NodeId` also allows the `DefCollector` to generate the `DefId`s instead
of lowering having to do it on the fly. Centralizing the `DefId` generation in one
place makes it easier to refactor and reason about.