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
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.
Reexport tests without polluting namespaces
This should fix issue #52557.
Basically now we gensym a new name for the test function and reexport that.
That way the test function's reexport name can't conflict because it was impossible for the test author to write it down.
We then use a `use` statement to expose the original name using the original visibility.
Andrew Chin 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.
rustc_resolve: record single-segment extern crate import resolutions.
Fixes#52489 by recording special-cased single-segment imports for later (e.g. stability) checks.
cc @alexcrichton @Mark-Simulacrum @petrochenkov
Does this need to be backported?
rustc: Trim down the `rust_2018_idioms` lint group
These migration lints aren't all up to par in terms of a good migration
experience. Some, like `unreachable_pub`, hit bugs like #52665 and unprepared
macros to be handled enough of the time. Others like linting against
`#[macro_use]` are swimming upstream in an ecosystem that's not quite ready (and
slightly buggy pending a few current PRs).
The general idea is that we will continue to recommend the `rust_2018_idioms`
lint group as part of the transition guide (as an optional step) but we'll be
much more selective about which lints make it into this group. Only those with a
strong track record of not causing too much churn will make the cut.
cc #52679
[NLL] Allow conflicting borrows of promoted length zero arrays
This is currently overkill as there's no way to create two conflicting borrows of any promoted.
It is possible that the following code might not fail due to const eval in the future (@oli-obk?). In which case either the array marked needs to not be promoted, or to be checked for conflicts
```rust
static mut A: () = {
let mut y = None;
let z;
let mut done_y = false;
loop {
let x = &mut [1]; // < this array
if done_y {
z = x;
break;
}
y = Some(x);
done_y = true;
}
some_const_fn(y, z); // some_const_fn expects that y to not alias z.
};
```
r? @pnkfelix @nikomatsakis
closes#52671
cc #51823
After talking about the PR with eddyb, I decided it was best to try to
have some test cases that simplify the problem down to its core, so
that people trying to understand what the issue is here will see those
core examples first.
(Presumably the place that borrow_check ends up reporting for the
error about is no longer the root `Local` itself, and thus the note
diagnostic here stops firing.)
These migration lints aren't all up to par in terms of a good migration
experience. Some, like `unreachable_pub`, hit bugs like #52665 and unprepared
macros to be handled enough of the time. Others like linting against
`#[macro_use]` are swimming upstream in an ecosystem that's not quite ready (and
slightly buggy pending a few current PRs).
The general idea is that we will continue to recommend the `rust_2018_idioms`
lint group as part of the transition guide (as an optional step) but we'll be
much more selective about which lints make it into this group. Only those with a
strong track record of not causing too much churn will make the cut.
cc #52679
rustc: Handle linker diagnostics from LLVM
Previously linker diagnostic were being hidden when two modules were linked
together but failed to link. This commit fixes the situation by ensuring that we
have a diagnostic handler installed and also adds support for handling linker
diagnostics.
Rollup of 30 pull requests
Successful merges:
- #52340 (Document From trait implementations for OsStr, OsString, CString, and CStr)
- #52628 (Cleanup some rustdoc code)
- #52732 (Remove unstable and deprecated APIs)
- #52745 (Update clippy to latest master)
- #52771 (Clarify thread::park semantics)
- #52778 (Improve readability of serialize.rs)
- #52810 ([NLL] Don't make "fake" match variables mutable)
- #52821 (pretty print for std::collections::vecdeque)
- #52822 (Fix From<LocalWaker>)
- #52824 (Fix -Wpessimizing-move warnings in rustllvm/PassWrapper)
- #52825 (Make sure #47772 does not regress)
- #52831 (remove references to AUTHORS.txt file)
- #52842 (update comment)
- #52846 (Add timeout to use of `curl` in bootstrap.py.)
- #52851 (Make the tool_lints actually usable)
- #52853 (Improve bootstrap help on stages)
- #52859 (Use Vec::extend in SmallVec::extend when applicable)
- #52861 (Add targets for HermitCore (https://hermitcore.org) to the Rust compiler and port libstd to it.)
- #52867 (releases.md: fix 2 typos)
- #52870 (Implement Unpin for FutureObj and LocalFutureObj)
- #52876 (run-pass/const-endianness: negate before to_le())
- #52878 (Fix wrong issue number in the test name)
- #52883 (Include lifetime in mutability suggestion in NLL messages)
- #52888 (Use suggestions for shell format arguments)
- #52904 (NLL: sort diagnostics by span)
- #52905 (Fix a typo in unsize.rs)
- #52907 (NLL: On "cannot move out of type" error, print original before rewrite)
- #52914 (Only run the sparc-abi test on sparc)
- #52918 (Backport 1.27.2 release notes)
- #52929 (Update compatibility note for 1.28.0 to be correct)
Failed merges:
r? @ghost
