[NLL] Use smaller spans for errors involving closure captures
Closes#51170Closes#46599
Error messages involving closures now point to the captured variable/closure args.
r? @pnkfelix
avoid computing liveness for locals that escape into statics
Fixes#52713
I poked at this on the plane and I think it's working -- but I want to do a bit more investigation and double check. The idea is to identify those local variables where the entire value will "escape" into the return -- for them, we don't need to compute liveness, since we know that the outlives relations from the return type will force those regions to be equal to free regions. This should help with html5ever in particular.
- [x] test performance
- [x] verify correctness
- [x] add comments
r? @pnkfelix
cc @lqd
App-lint-cability
@eminence recently pointed out (rust-lang/cargo#5846) that it's
surprising that `cargo fix` (now shipping with Cargo itself!) doesn't
fix very common lint warnings, which is as good of a reminder as any
that we should finish #50723.
(Previously, we did this on the librustc and libsyntax crates in #50724. I filed cmr/this-week-in-rust#685 in hopes of recruiting new contributors to do the rest.)
r? @estebank
Namely, the code here was trying to be clever, and say "lets not
report diagnostics when we 'know' NLL will report an error about them
in the future."
The problem is that in migration mode, when no error was reported here,
the NLL error that we "knew" was coming was downgraded to a warning (!).
This fixes that by only doing the "clever" skipping of region error reporting
when we are not in migration mode.
Rather than make a separate test for issue 53026, I just took the test
that uncovered this in a first place, and extended it (via our
revisions system) to explicitly show all three modes in action:
ACT-borrowck, NLL, and NLL migration mode.
(Tto be honest I hope not to have to add such revisions to many tests.
Instead I hope to adopt some sort of new `compare-mode` for either
borrowck=migrate or for the 2018 edition as a whole.)
Reintroduce `Undef` and properly check constant value sizes
r? @RalfJung
cc @eddyb
basically all kinds of silent failures that never occurred are assertions now
resolve: Implement prelude search for macro paths, implement tool attributes
When identifier is macro path is resolved in scopes (i.e. the first path segment - `foo` in `foo::mac!()` or `foo!()`), scopes are searched in the same order as for non-macro paths - items in modules, extern prelude, tool prelude (see later), standard library prelude, language prelude, but with some extra shadowing restrictions (names from globs and macro expansions cannot shadow names from outer scopes). See the comment in `fn resolve_lexical_macro_path_segment` for more details.
"Tool prelude" currently contains two "tool modules" `rustfmt` and `clippy`, and is searched immediately after extern prelude.
This makes the [possible long-term solution](https://github.com/rust-lang/rfcs/blob/master/text/2103-tool-attributes.md#long-term-solution) for tool attributes exactly equivalent to the existing extern prelude scheme, except that `--extern=my_crate` making crate names available in scope is replaced with something like `--tool=my_tool` making tool names available in scope.
The `tool_attributes` feature is still unstable and `#![feature(tool_attributes)]` now implicitly enables `#![feature(use_extern_macros)]`. `use_extern_macros` is a prerequisite for `tool_attributes`, so their stabilization will happen in the same order.
If `use_extern_macros` is not enabled, then tool attributes are treated as custom attributes (this is temporary, anyway).
Fixes https://github.com/rust-lang/rust/issues/52576
Fixes https://github.com/rust-lang/rust/issues/52512
Fixes https://github.com/rust-lang/rust/issues/51277
cc https://github.com/rust-lang/rust/issues/52269
[NLL] Dangly paths for box
Special-case `Box` in `rustc_mir::borrow_check`.
Since we know dropping a box will not access any `&mut` or `&` references, it is safe to model its destructor as only touching the contents *owned* by the box.
----
There are three main things going on here:
1. The first main thing, this PR is fixing a bug in NLL where `rustc` previously would issue a diagnostic error in a case like this:
```rust
fn foo(x: Box<&mut i32>) -> &mut i32 { &mut **x }
```
such code was accepted by the AST-borrowck in the past, but NLL was rejecting it with the following message ([playground](https://play.rust-lang.org/?gist=13c5560f73bfb16d6dab3ceaad44c0f8&version=nightly&mode=release&edition=2015))
```
error[E0597]: `**x` does not live long enough
--> src/main.rs:3:40
|
3 | fn foo(x: Box<&mut i32>) -> &mut i32 { &mut **x }
| ^^^^^^^^ - `**x` dropped here while still borrowed
| |
| borrowed value does not live long enough
|
note: borrowed value must be valid for the anonymous lifetime #1 defined on the function body at 3:1...
--> src/main.rs:3:1
|
3 | fn foo(x: Box<&mut i32>) -> &mut i32 { &mut **x }
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to previous error
```
2. The second main thing: The reason such code was previously rejected was because NLL (MIR-borrowck) incorporates a fix for issue #31567, where it models a destructor's execution as potentially accessing any borrows held by the thing being destructed. The tests with `Scribble` model this, showing that the compiler now catches such unsoundness.
However, that fix for issue #31567 is too strong, in that NLL (MIR-borrowck) includes `Box` as one of the types with a destructor that potentially accesses any borrows held by the box. This thus was the cause of the main remaining discrepancy between AST-borrowck and MIR-borrowck, as documented in issue #45696, specifically in [the last example of this comment](https://github.com/rust-lang/rust/issues/45696#issuecomment-345367873), which I have adapted into the `fn foo` shown above.
We did close issue #45696 back in December of 2017, but AFAICT that example was not fixed by PR #46268. (And we did not include a test, etc etc.)
This PR fixes that case, by trying to model the so-called `DerefPure` semantics of `Box<T>` when we traverse the type of the input to `visit_terminator_drop`.
3. The third main thing is that during a review of the first draft of this PR, @matthewjasper pointed out that the new traversal of `Box<T>` could cause the compiler to infinite loop. I have adjusted the PR to avoid this (by tracking what types we have previously seen), and added a much needed test of this somewhat odd scenario. (Its an odd scenario because the particular case only arises for things like `struct A(Box<A>);`, something which cannot be constructed in practice.)
Fix#45696.
