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Rollup merge of #113192 - lcnr:add-comment, r=compiler-errors

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`assemble_candidates_after_normalizing_self_ty` docs

I already explained that in different places a few times, should have added that explanation as a doc comment the first time I did so :3

r? `@BoxyUwU`
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Matthias Krüger 2023-07-04 17:46:26 +02:00 committed by GitHub
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17
compiler/rustc_trait_selection/src/solve/assembly/mod.rs
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@ -331,11 +331,20 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
candidates
}
/// If the self type of a goal is an alias, computing the relevant candidates is difficult.
/// If the self type of a goal is an alias we first try to normalize the self type
/// and compute the candidates for the normalized self type in case that succeeds.
///
/// To deal with this, we first try to normalize the self type and add the candidates for the normalized
/// self type to the list of candidates in case that succeeds. We also have to consider candidates with the
/// projection as a self type as well
/// These candidates are used in addition to the ones with the alias as a self type.
/// We do this to simplify both builtin candidates and for better performance.
///
/// We generate the builtin candidates on the fly by looking at the self type, e.g.
/// add `FnPtr` candidates if the self type is a function pointer. Handling builtin
/// candidates while the self type is still an alias seems difficult. This is similar
/// to `try_structurally_resolve_type` during hir typeck (FIXME once implemented).
///
/// Looking at all impls for some trait goal is prohibitively expensive. We therefore
/// only look at implementations with a matching self type. Because of this function,
/// we can avoid looking at all existing impls if the self type is an alias.
#[instrument(level = "debug", skip_all)]
fn assemble_candidates_after_normalizing_self_ty<G: GoalKind<'tcx>>(
&mut self,