🔬 Tracking issue for RFC 2089: Extended Implied bounds

[aturon]

This is a tracking issue for the RFC "Implied bounds" (rust-lang/rfcs#2089).

Steps:

• Implement the RFC (cc @rust-lang/compiler -- can anyone write up mentoring instructions?)
• Adjust documentation (see instructions on forge)
• Stabilization PR (see instructions on forge)

Unresolved questions:

• Should we try to limit the range of implied bounds to be crate-local (or module-local, etc)?
• @nikomatsakis pointed here that implied bounds can interact badly with current inference rules.

[skade]

I have a question not covered in the RFC (that not necessarily has to be part of the RFC): what will error reporting on bounds violations look like? Will it point to the original definition of the bound?

[ExpHP]

I'm not part of this, but I'll summarize what appears to be the current state of this feature from what I can find:

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This tracking issue was posted shortly before the 2017 impl period began, and it looks like it fell under the scope of the WG-compiler-traits workgroup. On the workgroup's dropbox doc I see (under Query model):

We do have to handle cycles at least as well as chalk for implied bounds to work out

I searched the issue tracker for recent issues/PRs about bound cycles or the query model, but nothing stood out.