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Document speculative crate loading (#859)

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Joshua Nelson 2020-09-09 03:19:01 -04:00 committed by GitHub
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src/name-resolution.md
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@ -145,6 +145,23 @@ the code can be processed.
Therefore, the resolution is performed in multiple stages. Therefore, the resolution is performed in multiple stages.
## Speculative crate loading
To give useful errors, rustc suggests importing paths into scope if they're
not found. How does it do this? It looks through every module of every crate
and looks for possible matches. This even includes crates that haven't yet
been loaded!
Loading crates for import suggestions that haven't yet been loaded is called
_speculative crate loading_, because any errors it encounters shouldn't be
reported: resolve decided to load them, not the user. The function that does
this is `lookup_import_candidates` and lives in
`rustc_resolve/src/diagnostics.rs`.
To tell the difference between speculative loads and loads initiated by the
user, resolve passes around a `record_used` parameter, which is `false` when
the load is speculative.
## TODO: ## TODO:
This is a result of the first pass of learning the code. It is definitely This is a result of the first pass of learning the code. It is definitely