Keep more information about trait binding failures.

…=nikomatsakis,eddyb

Use `PredicateObligation`s instead of `Predicate`s

Keep more information about trait binding failures. Use more specific spans by pointing at bindings that introduce obligations.

Subset of rust-lang#69709.

r? @eddyb

…ruppe

Add ThreadSanitizer test case

…nas-schievink

Use forward traversal for unconditional recursion lint

While reviewing rust-lang#70822, I noted that rust-lang#54444 could be solved without requiring the predecessor graph and without allocating a `Vec<Span>` for every basic block. The unconditional recursion lint is not a performance bottleneck however, so I approved rust-lang#70822 as it was.

Nevertheless, I wanted to try implementing my idea using `TriColorDepthFirstSearch`, which is a DFS that can differentiate between [forward/tree edges and backward ones](https://en.wikipedia.org/wiki/Depth-first_search#Output_of_a_depth-first_search). I found this approach more straightforward than the existing one, so I'm opening this PR to see if it is desirable.

The pass is now just a DFS across the control-flow graph. We ignore false edges and false unwinds, as well as the successors of recursive calls, just like existing pass does. If we see a back-edge (loop) or a terminator that would cause us to yield control-flow back to the caller (`Return`, `Resume`, etc.), we know that the function does not unconditionally recurse.

r? @jonas-schievink

…Simulacrum

compiletest: let config flags overwrite -A unused

Cc Manishearth/compiletest-rs#216

…ariations, r=Amanieu

Follow up on BTreeMap comments

r? @Amanieu (for the first commit)

…Mark-Simulacrum

Rearrange BTreeMap::into_iter to match range_mut.

r? @Mark-Simulacrum
I wondered why you catered for the optional root differently in `into_iter` than in `range_mut`.

…an-DPC

Clean up E0512 explanation

r? @Dylan-DPC

…e, r=Mark-Simulacrum

Setup the `@rustbot prioritize` command

See rust-lang/triagebot#453

r? @Mark-Simulacrum can you confirm that the `t-compiler/wg-prioritization` stream ID is `227806`?
cc @spastorino

fix rustc-dev-guide's url in src/librustc_codegen_ssa

Change the backend-agnostic chapter's url in rustc-dev-guide from [url](https://rustc-dev-guide.rust-lang.org/codegen/backend-agnostic.html), which is 404 now, to [the right one](https://rustc-dev-guide.rust-lang.org/backend/backend-agnostic.html).

Sorry for disturbing.