Add derive_ord_xor_partial_ord lint
Fix#1621
Some remarks:
This PR follows the example of the analogous derive_hash_xor_partial_eq lint where possible.
I initially tried using the `match_path` function to identify `Ord` implementation like the derive_hash_xor_partial_eq lint currently does, for `Hash` implementations but that didn't work.
Specifically, the structs at the top level were getting paths that matched `&["$crate", "cmp", "Ord"]` instead of `&["std", "cmp", "Ord"]`. While trying to figure out what to do instead I saw the comment at the top of [clippy_lints/src/utils/paths.rs](f5d429cd76/clippy_lints/src/utils/paths.rs (L5)) that mentioned [this issue](https://github.com/rust-lang/rust-clippy/issues/5393) and suggested to use diagnostic items instead of hardcoded paths whenever possible. I looked for a way to identify `Ord` implementations with diagnostic items, but (possibly because this was the first time I had heard of diagnostic items,) I was unable to find one.
Eventually I tried using `get_trait_def_id` and comparing `DefId` values directly and that seems to work as expected. Maybe there's a better approach however?
changelog: new lint: derive_ord_xor_partial_ord
Handle mapping to Option in `map_flatten` lint
Fixes#4496
The existing [`map_flatten`](https://rust-lang.github.io/rust-clippy/master/index.html#map_flatten) lint suggests changing `expr.map(...).flatten()` to `expr.flat_map(...)` when `expr` is `Iterator`. This PR changes suggestion to `filter_map` instead of `flat_map` when mapping to `Option`, because it is more natural
Also here are some questions:
* If expression has type which implements `Iterator` trait (`match_trait_method(cx, expr, &paths::ITERATOR) == true`), how can I get type of iterator elements? Currently I use return type of closure inside `map`, but probably it is not good way
* I would like to change suggestion range to cover only `.map(...).flatten()`, that is from:
```
let _: Vec<_> = vec![5_i8; 6].into_iter().map(|x| 0..x).flatten().collect();
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try using `flat_map` instead: `vec![5_i8; 6].into_iter().flat_map
```
to
```
let _: Vec<_> = vec![5_i8; 6].into_iter().map(|x| 0..x).flatten().collect();
^^^^^^^^^^^^^^^^^^^^^^^^ help: try using `flat_map` instead: `.flat_map(|x| 0..x)`
```
Is it ok?
* Is `map_flatten` lint intentionally in `pedantic` category, or could it be moved to `complexity`?
changelog: Handle mapping to Option in [`map_flatten`](https://rust-lang.github.io/rust-clippy/master/index.html#map_flatten) lint
needless_collect: catch x: Vec<_> = iter.collect(); x.into_iter() ...
changelog: Expand the needless_collect lint as suggested in #5627 (WIP).
This PR is WIP because I can't figure out how to make the multi-part suggestion include its changes in the source code (the fixed is identical to the source, despite the lint making suggestions). Aside from that one issue, I think this should be good.
For consistency with `Attribute::has_name` which doesn't mark the attribute as used either.
Replace all uses of `check_name` with `has_name` outside of rustc
There are two different implementation of Try trait for Poll type;
Poll<Result<T, E>> and Poll<Option<Result<T, E>>>. Take them into
account when generating suggestions.
For example, for Err(e)? suggest either return Poll::Ready(Err(e)) or
return Poll::Ready(Some(Err(e))) as appropriate.
Fix ui-cargo tests in CI
r? @ebroto
The `ui-toml` tests set the `CARGO_MANIFEST_DIR` var, but never reset it, so the `ui-cargo` tests used it also and then found a faulty `clippy.toml` file
changelog: none
The reason we do not trigger these lints anymore is that clippy sets the mir-opt-level to 0, and the recent changes subtly changed how the const propagator works.
Basic instruction for new contributors
While answering a few questions to @AB1908, I realized, that our documentation could use some love. Especially the "Getting Started" part for new contributors. So I wrote together some instruction on how to get the toolchain and how to build and test Clippy.
[Rendered](https://github.com/flip1995/rust-clippy/blob/basics/doc/basics.md)
r? @phansch
changelog: none
Small fix: `chmod` 644 `clippy_lints/src/utils/ast_utils.rs`
changelog: none
It looks like `clippy_lints/src/utils/ast_utils.rs` doesn't have to be an executable file.
