[NLL] Fix some things for bootstrap
Some changes that are required when bootstrapping rustc with NLL enabled.
* Remove a bunch of unused `mut`s that aren't needed, but the existing lint doesn't catch.
* Rewrite a function call to satisfy NLL borrowck. Note that the borrow is two-phase, but gets activated immediately by an unsizing coercion.
cc #51823
Don't format!() string literals
Prefer `to_string()` to `format!()` take 2, this time targetting string literals. In some cases (`&format!("...")` -> `"..."`) also removes allocations. Occurences of `format!("")` are changed to `String::new()`.
Replace push loops with extend() where possible
Or set the vector capacity where I couldn't do it.
According to my [simple benchmark](https://gist.github.com/ljedrz/568e97621b749849684c1da71c27dceb) `extend`ing a vector can be over **10 times** faster than `push`ing to it in a loop:
10 elements (6.1 times faster):
```
test bench_extension ... bench: 75 ns/iter (+/- 23)
test bench_push_loop ... bench: 458 ns/iter (+/- 142)
```
100 elements (11.12 times faster):
```
test bench_extension ... bench: 87 ns/iter (+/- 26)
test bench_push_loop ... bench: 968 ns/iter (+/- 3,528)
```
1000 elements (11.04 times faster):
```
test bench_extension ... bench: 311 ns/iter (+/- 9)
test bench_push_loop ... bench: 3,436 ns/iter (+/- 233)
```
Seems like a good idea to use `extend` as much as possible.
Rollup of 11 pull requests
Successful merges:
- #52702 (Suggest fix when encountering different mutability from impl to trait)
- #52703 (Improve a few vectors - calculate capacity or build from iterators)
- #52740 (Suggest underscore when using dashes in crate namet push fork)
- #52759 (Impl Send & Sync for JoinHandle)
- #52760 (rustc_metadata: test loading atoi instead of cos)
- #52763 (Omit the vendor component in Fuchsia triple)
- #52765 (Remove unused "-Zenable_nonzeroing_move_hints" flag)
- #52769 (Incorporate a stray test)
- #52777 (Fix doc comment for 'ptr::copy_to' method)
- #52779 (revert accidental atty downgrade)
- #52781 (Use a slice where a vector is not necessary)
Failed merges:
r? @ghost
[NLL] Use better spans in some errors
* Use the span of the discriminant and patterns for "fake" statements created to properly check matches. I plan to special case these soon, but this felt like a good first step
* Use the span of the statement, rather than the initialization, when reporting move errors for `let x = ...`, which avoids giving an unhelpful suggestion to use `&{ }`.
r? @nikomatsakis cc @pnkfelix
Rollup of bare_trait_objects PRs
All deny attributes were moved into bootstrap so they can be disabled with a line of config.
Warnings for external tools are allowed and it's up to the tool's maintainer to keep it warnings free.
r? @Mark-Simulacrum
cc @ljedrz @kennytm
[NLL] make temp for each candidate in `match` arm
In NLL, `ref mut` patterns leverage the two-phase borrow infrastructure to allow the shared borrows within a guard before the "activation" of the mutable borrow when we begin execution of the match arm's body. (There is further discussion of this on PR #50783.)
To accommodate the restrictions we impose on two-phase borrows (namely that there is a one-to-one mapping between each activation and the original initialization), this PR is making separate temps for each candidate pattern. So in an arm like this:
```rust
PatA(_, ref mut ident) |
PatB(ref mut ident) |
PatC(_, _, ref mut ident) |
PatD(ref mut ident) if guard_stuff(ident) => ...
```
instead of 3 temps (two for the guard and one for the arm body), we now have 4 + 2 temps associated with `ident`: one for each candidate plus the actual temp that the guard uses directly, and then the sixth is the temp used in the arm body.
Fix#51348
Add `-Z borrowck=migrate`
This adds `-Z borrowck=migrate`, which represents the way we want to migrate to NLL under Rust versions to come. It also hooks this new mode into `--edition 2018`, which means we're officially turning NLL on in the 2018 edition.
The basic idea of `-Z borrowck=migrate` that there are cases where NLL is fixing old soundness bugs in the borrow-checker, but in order to avoid just breaking code by immediately rejecting the programs that hit those soundness bugs, we instead use the following strategy:
If your code is accepted by NLL, then we accept it.
If your code is rejected by both NLL and the old AST-borrowck, then we reject it.
If your code is rejected by NLL but accepted by the old AST-borrowck, then we emit the new NLL errors as **warnings**.
These warnings will be turned into hard errors in the future, and they say so in these diagnostics.
Fix#46908
Rollup of 16 pull requests
Successful merges:
- #52558 (Add tests for ICEs which no longer repro)
- #52610 (Clarify what a task is)
- #52617 (Don't match on region kinds when reporting NLL errors)
- #52635 (Fix #[linkage] propagation though generic functions)
- #52647 (Suggest to take and ignore args while closure args count mismatching)
- #52649 (Point spans to inner elements of format strings)
- #52654 (Format linker args in a way that works for gcc and ld)
- #52667 (update the stdsimd submodule)
- #52674 (Impl Executor for Box<E: Executor>)
- #52690 (ARM: expose `rclass` and `dsp` target features)
- #52692 (Improve readability in a few sorts)
- #52695 (Hide some lints which are not quite right the way they are reported to the user)
- #52718 (State default capacity for BufReader/BufWriter)
- #52721 (std::ops::Try impl for std::task::Poll)
- #52723 (rustc: Register crates under their real names)
- #52734 (sparc ABI issue - structure returning from function is returned in 64bit registers (with tests))
Failed merges:
- #52678 ([NLL] Use better spans in some errors)
r? @ghost
Don't match on region kinds when reporting NLL errors
First half (by number of tests affected) of the changes to "does not live long enough".
Now that lexical MIR borrowck is gone, region kinds are always ReVar, so matching on them to change errors does nothing.
Changes "borrowed value only lives until here" to "`x` is dropped here while still borrowed".
r? @pnkfelix cc @nikomatsakis
Also convert an ICE that became reachable code under borrowck=migrate
into a normally reported error (which is then downgraded to a
warning). This actually has a nice side benefit of providing a
somewhat more useful error message, at least in the particular case of
the example from issue #27282.
This required a bit of plumbing to keep track of candidates. But I
took advantage of the hack session to try to improve the docs for the
relevant structs here.
(I also tried to simplify some of the related code in passing.)
