This commit adds a lint to the compiler to warn against the `#[macro_use]`
directive as part of the `rust_2018_idioms` lint. This lint is turned off by
default and is only enabled when the `use_extern_macros` feature is also
enabled.
The lint here isn't fully fleshed out as it's just a simple warning rather than
suggestions of how to actually import the macro, but hopefully it's a good base
to start from!
cc #52043
Add lint checks for unused loop labels
Previously no warning was generated when a loop label was written out but never used (i.e. in a `break` or `continue` statement):
```rust
fn main() {
'unused_label: loop {}
}
```
would compile without complaint.
This fix introduces `-W unused_loop_label`, which generates the following warning message for the above snippet:
```
warning: unused loop label
--> main.rs:2:5
|
2 | 'unused_label: loop {}
| ^^^^^^^^^^^^^
|
= note: #[warn(unused_loop_label)] on by default
```
Fixes: #50751.
Turn deprecation lint `legacy_imports` into a hard error
Closes https://github.com/rust-lang/rust/issues/38260
The lint was introduced in Dec 2016, then made deny-by-default in Jun 2017 when crater run found 0 regressions caused by it.
This lint requires some not entirely trivial amount of import resolution logic that (surprisingly or not) interacts with `feature(use_extern_macros)` (https://github.com/rust-lang/rust/issues/35896), so it would be desirable to remove it before stabilizing `use_extern_macros`.
In particular, this PR fixes the failing example in https://github.com/rust-lang/rust/issues/50725 (but not the whole issue, `use std::panic::{self}` still can cause other undesirable errors when `use_extern_macros` is enabled).
Make the `const_err` lint `deny`-by-default
At best these things are runtime panics (debug mode) or overflows (release mode). More likely they are public constants that are unused in the crate declaring them.
This is not a breaking change, as dependencies won't break and root crates can `#![warn(const_err)]`, though I don't know why anyone would do that.
Improve single-use and zero-use lifetime lints
The code now correctly identifies *when* to lint -- or more correctly, anyhow -- but it doesn't yet offer suggestions for how to fix.
(I just remembered when writing this I had meant to go back over some of these cases around e.g. impl Trait and double check that everything is right...)
cc #44752
r? @cramertj
lint: deny incoherent_fundamental_impls by default
Warn the ecosystem of the pending intent-to-disallow in #49799.
There are 4 ICEs on my machine, look unrelated (having happened before in https://github.com/rust-lang/rust/issues/49146#issuecomment-384473523)
```rust
thread 'main' panicked at 'assertion failed: position <= slice.len()', libserialize/leb128.rs:97:1
```
```
[run-pass] run-pass/allocator/xcrate-use2.rs
[run-pass] run-pass/issue-12133-3.rs
[run-pass] run-pass/issue-32518.rs
[run-pass] run-pass/trait-default-method-xc-2.rs
```
r? @nikomatsakis
This was added to cover up a lazy extra semicolon in #35849, but does
not actually make sense. This is removed as a part of the stabilization
of `never_type`.
This updates the borrowck query to return a result, and this result is then used
to incrementally check for unused mutable nodes given sets of all the used
mutable nodes.
Closes#42384
