polymorphize: I used if T used in I: Foo<T>
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rust-highfive
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lcnr
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lcnr
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This commit adjusts polymorphization's handling of predicates so that after ensuring that `T` is used in `I: Foo<T>` if `I` is used, it now ensures that `I` is used if `T` is used in `I: Foo<T>`. This is necessary to mark generic parameters that only exist in impl parameters as used - thereby avoiding symbol clashes when using the new mangling scheme. Signed-off-by: David Wood <david@davidtw.co>
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While I think that this restriction is somewhat unfortunate this does look correct to me now. @bors r+ rollup |
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📌 Commit bf3ef26 has been approved by |
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| @@ -318,3 +373,36 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for UsedGenericParametersVisitor<'a, 'tcx> { | |||
| } | |||
| } | |||
| } | |||
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| /// Visitor used to check if a generic parameter is used. | |||
| struct IsUsedGenericParams<'a> { | |||
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Maybe this should be called HasUsedGenericParams?
eddyb
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Aug 14, 2020
| debug!("mark_used_by_predicates: checking projection ty"); | ||
| if is_ty_used(unused_parameters, proj.ty) { | ||
| debug!("mark_used_by_predicates: used!"); | ||
| mark_ty(unused_parameters, self_ty); |
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I think this is overly simplistic, I suspect you can replace I: Iterator<...> with (): WeirdIterator<I, ...>.
Any treatment of the Self parameter as special is suspicious by default, IMO.
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| // Consider `T` used if `I` is used in predicates of the form | ||
| // `I: Iterator<Item = T>` | ||
| debug!("mark_used_by_predicates: checking self"); | ||
| if is_ty_used(unused_parameters, trait_ref.self_ty()) { | ||
| debug!("mark_used_by_predicates: used!"); | ||
| for ty in trait_ref.substs.types() { | ||
| mark_ty(unused_parameters, ty); | ||
| } | ||
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| // No need to check for a type being used in the substs if `self_ty` was | ||
| // used. | ||
| continue; | ||
| } | ||
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| // Consider `I` used if `T` is used in predicates of the form | ||
| // `I: Iterator<Item = &'a (T, E)>` (see rust-lang/rust#75326) | ||
| debug!("mark_used_by_predicates: checking substs"); | ||
| for ty in trait_ref.substs.types() { | ||
| debug!("unused_generic_params: (trait) ty={:?}", ty); | ||
| mark_ty(unused_parameters, ty); | ||
| if is_ty_used(unused_parameters, ty) { | ||
| debug!("mark_used_by_predicates: used!"); | ||
| mark_ty(unused_parameters, trait_ref.self_ty()); | ||
| } | ||
| } | ||
| } |
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This sounds like an overly complicated way to handle "if any parameters are used, all are".
Notable strangeness:
substs.types()will includeself_tyso some of this code already seems redundant with itself.types()makes me wonder: what about const generics?
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☀️ Test successful - checks-actions, checks-azure |
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I'll address @eddyb's comments in a follow-up. |
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Aug 20, 2020
…simplification-correction, r=eddyb polymorphize: if any param in a predicate is used, then all are used Addresses [review](rust-lang#75518 (comment)) [comments](rust-lang#75518 (comment)) [from](rust-lang#75518 (comment)) @eddyb in rust-lang#75518 that I didn't get to resolve before bors merged. This PR modifies polymorphization's handling of predicates so that if any generic parameter is used in a predicate then all parameters in that predicate are used. r? @eddyb
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Fixes #75326.
This PR adjusts polymorphization's handling of predicates so that after ensuring that
Tis used inI: Foo<T>ifIis used, it now ensures thatIis used ifTis used inI: Foo<T>. This is necessary to mark generic parameters that only exist in impl parameters as used - thereby avoiding symbol clashes when using the new mangling scheme.With this PR, rustc will now fully bootstrap with polymorphization and the new symbol mangling scheme enabled - not all tests pass, but I'm not sure how much of that is the interaction of the two features, I'll be looking into that soon. All tests pass with only polymorphization enabled.
r? @lcnr (this isn't sufficiently complex that I need to add to eddy's review queue)
cc @eddyb