[chalkify] duplicate predicates with predicates_defined_on #52187

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1. scalexm

   self-assigned this

   on Jul 9, 2018
2. scalexm commented on Jul 27, 2018

   

   scalexm

   on Jul 27, 2018

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   Hint: this duplication is only triggered when using the following form for a super trait:

   trait Bar where Self: Foo {}

   For the alternative syntax trait Bar: Foo {} as well as any where clause not of the form Self: ..., the output seems fine.
3. scalexm commented on Jul 27, 2018

   

   scalexm

   on Jul 27, 2018

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   Ok found the culprit: explicit_predicates_of collects the where clauses explicitly written on the trait, and then also adds those returned by super_predicates_of. But super_predicates_of collects both the « inline » super trait bounds e.g. trait Bar: Foo and the ones included as where clauses e.g. where Self: Foo, but the where Self: Foo was already collected before calling super_predicates_of, hence the duplicate.

   Overall, this is not a big problem apart from giving chalk (and maybe some parts of rustc not using e.g. a HashMap or HashSet) the same clause twice. However for clean outputs, I’d just suggest having an additional explicit_super_predicates_of or something like that (which would not need to be added as a query), which would only return super trait bounds written in the form trait Bar: Foo and which would be used by explicit_predicates_of.

   cc @nikomatsakis
4. nikomatsakis commented on Aug 8, 2018

   

   nikomatsakis

   on Aug 8, 2018

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   Sounds about right to me
5. emilyalbini

   added 2 commits that reference this issue on Oct 3, 2018

   Rollup merge of rust-lang#54780 - scalexm:dup-predicates, r=nikomatsakis

   ...

   009f32e

   Rollup merge of rust-lang#54780 - scalexm:dup-predicates, r=nikomatsakis

   ...

   cbc9477
6. bors

   closed this as completedin 8327976on Oct 4, 2018
7. tmandry

   added

   WG-traits

   on May 24, 2023