In particular, -Znll might as well imply -Zborrowck=mir by default,
just like `#![feature(nll)]` does.
Also, if NLL is in use, no reason to emit end regions. The NLL pass
just strips them out anyway.
nll part 5
Next round of changes from the nll-master branch.
Extensions:
- we now propagate ty-region-outlives constraints out of closures and into their creator when necessary
- we fix a few ICEs that can occur by doing liveness analysis (and the resulting normalization) during type-checking
- we handle the implicit region bound that assumes that each type `T` outlives the fn body
- we handle normalization of inputs/outputs in fn signatures
Not included in this PR (will come next):
- handling `impl Trait`
- tracking causal information
- extended errors
r? @arielb1
Point at var in short lived borrows instead of drop location
For RLS' sake, point at the borrow location as primary span for short lived borrows, instead of the borrow drop location.
Fix#39268.
The input/output types found in `UniversalRegions` are not normalized.
The old code used to assign them directly into the MIR, which would
lead to errors when there was a projection in a argument or return
type. This also led to some special cases in the `renumber` code.
We now renumber uniformly but then pass the input/output types into
the MIR type-checker, which equates them with the types found in MIR.
This allows us to normalize at the same time.
This allows us to re-use the `normalize` method on `TypeCheck`, which
is important since normalization may create fresh region
variables. This is not an ideal solution, though, since the current
representation of "liveness constraints" (a vector of (region, point)
pairs) is rather inefficient. Could do somewhat better by converting
to indices, but it'd still be less good than the older code. Unclear
how important this is.
Before, we would always have a `Some` ClosureRegionRequirements if we
were inferring values for a closure. Now we only do is it has a
non-empty set of outlives requirements.
[MIR-borrowck] Two phase borrows
This adds limited support for two-phase borrows as described in
http://smallcultfollowing.com/babysteps/blog/2017/03/01/nested-method-calls-via-two-phase-borrowing/
The support is off by default; you opt into it via the flag `-Z two-phase-borrows`
I have written "*limited* support" above because there are simple variants of the simple `v.push(v.len())` example that one would think should work but currently do not, such as the one documented in the test compile-fail/borrowck/two-phase-reservation-sharing-interference-2.rs
(To be clear, that test is not describing something that is unsound. It is just providing an explicit example of a limitation in the implementation given in this PR. I have ideas on how to fix, but I want to land the work that is in this PR first, so that I can stop repeatedly rebasing this branch.)
