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Enforce that closure: 'a requires that closure_ret_ty: 'a holds #84385

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wants to merge 3 commits into from
Closed

Enforce that closure: 'a requires that closure_ret_ty: 'a holds #84385

wants to merge 3 commits into from
+224 −28

Commits on Oct 7, 2022

  1. Enforce that closure: 'a requires that closure_ret_ty: 'a holds 

    RFC 1214 allows us to infer that `<T as Trait<P0, ... PN>>::Out: 'a`
holds, so long as `T: 'a, P0: 'a, ..., PN: 'a` all hold.

In order for this to be sound, we must ensure that whenever we need to
prove `T: 'a` for some concrete type `T`, we also ensure that
any type which could appear in the output type for an impl also outlives
`'a`

However, we failed to enforce this for closures. Specifically, we
allowed `closure: 'a` to hold without requiring that `closure_ret_ty:
'a` also holds. Since `closure_ret_ty` appears in the output of the
`FnOnce` impl for closures, it was possible to extend a lifetime by
causing rustc to assume that the closure return type outlived a lifetime
based on the fact that the closure itself outlived a lifetime.

This commit includes the closure return type as one of the 'components'
used when computing outlives requirements. To minimize the extent of
this breaking change, we do *not* include the arguments of the closure
as 'components'. Doing so is still sound, but introduces an
inconsistency with function pointers (which do treat their arguments as
'components')

Several uses of closures in libcore needed to be adjusted, all of them
involving returning a closure via an `impl Fn` opaque type. In all
cases, we needed to add extra lifetime bounds to generic parameters that
ended up in the return type `R` of `impl Fn() -> R`.
    @Aaron1011
    Aaron1011 committed Oct 7, 2022
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  2. Fix closure return type lifetimes in rustc itself

    @Aaron1011
    Aaron1011 committed Oct 7, 2022
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  3. [DO NOT MERGE] [CRATER] Only enable when CARGO_PRIMARY_PACKAGE is set

    @Aaron1011
    Aaron1011 committed Oct 7, 2022
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