From the current nightly docs for AsRef:  Looks like this was introduced in https://github.com/rust-lang/rust/pull/44275.
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eddyb commentedon Sep 14, 2017
Linking an issue number doesn't cc anyone, sadly.
Fix incoming.
Rollup merge of rust-lang#44562 - eddyb:ugh-rustdoc, r=nikomatsakis
Rollup merge of rust-lang#44562 - eddyb:ugh-rustdoc, r=nikomatsakis
Rollup merge of rust-lang#44562 - eddyb:ugh-rustdoc, r=nikomatsakis
Rollup merge of rust-lang#44562 - eddyb:ugh-rustdoc, r=nikomatsakis
Rollup merge of rust-lang#44562 - eddyb:ugh-rustdoc, r=nikomatsakis