Rework suggestion generation of `unit_arg` lint
Found this bug while running `cargo fix --clippy` on quite a big codebase:
This would replace something like:
```rust
Some(fn_that_actually_does_something(&a, b))
```
with
```rust
Some(())
```
which obviously suppresses side effects.
Since pretty much every expression could have side effects, I think making this suggestion `MaybeIncorrect` is the best thing to do here.
A correct suggestion would be:
```rust
fn_that_actually_does_something(&a, b);
Some(())
```
Somehow the suggestion is not correctly applied to the arguments, when more than one argument is a unit value. I have to look into this a little more, though.
changelog: Fixes suggestion of `unit_arg` lint, so that it suggests semantic equivalent code
Fixes#4741
len_zero: skip ranges if feature `range_is_empty` is not enabled
If the feature is not enabled, calling `is_empty()` on a range is ambiguous. Moreover, the two possible resolutions are unstable methods, one inherent to the range and the other being part of the `ExactSizeIterator` trait.
Since `len_zero` only checks for existing `is_empty()` inherent methods, we only take into account the `range_is_empty` feature.
Related: https://github.com/rust-lang/rust/issues/48111#issuecomment-445132965
changelog: len_zero: avoid linting ranges without #![feature(range_is_empty)]
Fixes: #3807
Extend useless conversion
This PR extends `useless_conversion` lint with `TryFrom` and `TryInto`
fixes: #5344
changelog: Extend `useless_conversion` with `TryFrom` and `TryInto`
Make empty_line_after_outer_attr an early lint
Fixes#5567
Unfortunately I couldn't find a way to reproduce the issue without syn/quote. Considering that most real-world macros use syn and/or quote, I think it's okay to pull them in anyway.
changelog: Fix false positive in [`empty_line_after_outer_attr`]
reversed_empty_ranges: add suggestion for &slice[N..N]
As discussed in the issue thread, the user accepted this solution. Let me know if this is what we want, or if changing the way we lint the N..N case is prefered.
changelog: reversed_empty_ranges: add suggestion for &slice[N..N]
Closes#5628
ptr_arg: honor `allow` attribute on arguments
The `intravisit::Visitor` impl for `LateContextAndPass` only takes into account the attributes of a function parameter inside the `check_param` method. `ptr_arg` starts its heuristics at `check_item` / `check_impl_item` / `check_trait_item`, so the `allow` is not taken into account automatically.
changelog: ptr_arg: honor `allow` attribute on arguments
Fixes#5644
