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Use is_global in candidate_should_be_dropped_in_favor_of #90375

Merged
merged 3 commits into from
Oct 30, 2021
Merged

Use is_global in candidate_should_be_dropped_in_favor_of #90375

merged 3 commits into from
Oct 30, 2021

Commits on Oct 28, 2021

  1. Use is_global in candidate_should_be_dropped_in_favor_of 

    This manifistated in rust-lang#90195 with compiler being unable to keep
one candidate for a trait impl, if where is a global impl and more
than one trait bound in the where clause.

Before rust-lang#87280 `candidate_should_be_dropped_in_favor_of` was using
`TypeFoldable::is_global()` that was enough to discard the two
`ParamCandidate`s. But rust-lang#87280 changed it to use
`TypeFoldable::is_known_global()` instead, which is pessimistic, so
now the compiler drops the global impl instead (because
`is_known_global` is not sure) and then can't decide between the
two `ParamCandidate`s.

Switching it to use `is_global` again solves the issue.

Fixes rust-lang#90195.
    @yanok
    yanok committed Oct 28, 2021
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  2. Reformat the changed line to make tidy happy

    @yanok
    yanok committed Oct 28, 2021
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  3. Add test cases

    @yanok
    yanok committed Oct 28, 2021
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