Uplift `clippy::for_loops_over_fallibles` lint into rustc
This PR, as the title suggests, uplifts [`clippy::for_loops_over_fallibles`] lint into rustc. This lint warns for code like this:
```rust
for _ in Some(1) {}
for _ in Ok::<_, ()>(1) {}
```
i.e. directly iterating over `Option` and `Result` using `for` loop.
There are a number of suggestions that this PR adds (on top of what clippy suggested):
1. If the argument (? is there a better name for that expression) of a `for` loop is a `.next()` call, then we can suggest removing it (or rather replacing with `.by_ref()` to allow iterator being used later)
```rust
for _ in iter.next() {}
// turns into
for _ in iter.by_ref() {}
```
2. (otherwise) We can suggest using `while let`, this is useful for non-iterator, iterator-like things like [async] channels
```rust
for _ in rx.recv() {}
// turns into
while let Some(_) = rx.recv() {}
```
3. If the argument type is `Result<impl IntoIterator, _>` and the body has a `Result<_, _>` type, we can suggest using `?`
```rust
for _ in f() {}
// turns into
for _ in f()? {}
```
4. To preserve the original behavior and clear intent, we can suggest using `if let`
```rust
for _ in f() {}
// turns into
if let Some(_) = f() {}
```
(P.S. `Some` and `Ok` are interchangeable depending on the type)
I still feel that the lint wording/look is somewhat off, so I'll be happy to hear suggestions (on how to improve suggestions :D)!
Resolves#99272
[`clippy::for_loops_over_fallibles`]: https://rust-lang.github.io/rust-clippy/master/index.html#for_loops_over_fallibles
rename `ImplItemKind::TyAlias` to `ImplItemKind::Type`
The naming of this variant seems inconsistent given that this is not really a "type alias", and the associated type variant for `TraitItemKind` is just called `Type`.
Further enhance `needless_borrow`, mildly refactor `redundant_clone`
This PR does the following:
* Moves some code from `redundant_clone` into a new `clippy_utils` module called `mir`, and wraps that code in a function called `dropped_without_further_use`.
* Relaxes the "is copyable" condition condition from #9136 by also suggesting to remove borrows from values dropped without further use. The changes involve the just mentioned function.
* Separates `redundant_clone` into modules.
Strictly speaking, the last bullet is independent of the others. `redundant_clone` is somewhat hairy, IMO. Separating it into modules makes it slightly less so, by helping to delineate what depends upon what.
I've tried to break everything up into digestible commits.
r? `@Jarcho`
(`@Jarcho` I hope you don't mind.)
changelog: continuation of #9136
Add `manual_filter` lint for `Option`
Share much of its implementation with `manual_map` and should greatly benefit from its previous feedback.
I'm sure it's possible to even more refactor both and would gladly take input on that as well as any clippy idiomatic usage, since this is my first lint addition.
I've added the lint to the complexity section for now, I don't know if every new lint needs to go in nursery first.
The matching could be expanded to more than `Some(<value>)` to lint on arbitrary struct matching inside the `Some` but I've left it like it was for `manual_map` for now. `needless_match::pat_same_as_expr` provides a more generic match example.
close https://github.com/rust-lang/rust-clippy/issues/8822
changelog: Add lint [`manual_filter`] for `Option`
extend `box-default` lint, add suggestion
This extends the recently added `box-default` lint to also cover `Box::new(vec![])`, `Box::new(String::from(""))` and `Box::new(Vec::from([]))`. Also the lint now suggests a suitable replacement. I did not find a simple way to check whether the type is fully determined by the outside, so I at least checked for some variations to remove the turbofish in those cases.
---
changelog: none
lint::unsafe_removed_from_name: fix false positive result when allowed
changelog: [`unsafe_removed_from_name`] Fix allowing on imports produces a false positive on `useless_attribute`.
Fixes: #9197
Signed-off-by: Andy-Python-Programmer <andypythonappdeveloper@gmail.com>
FormatArgsExpn: Find comma spans and ignore weird proc macro spans
Fixes the following cases:
A missing `, 1` from the `expect_fun_call` suggestion:
```rust
Some(()).expect(&format!("{x} {}", 1));
```
```
warning: use of `expect` followed by a function call
--> t.rs:7:14
|
7 | Some(()).expect(&format!("{x} {}", 1));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `unwrap_or_else(|| panic!("{x} {}"))`
```
The suggestion removing from the comma in the comment rather than the one after the format string:
```rust
println!(
"{}",
// a comment, with a comma in it
x
);
```
```
warning: variables can be used directly in the `format!` string
--> t.rs:9:5
|
9 | / println!(
10 | | "{}",
11 | | // a comment, with a comma in it
12 | | x
13 | | );
| |_____^
|
help: change this to
|
10 ~ "{x}",
11 ~ // a comment
|
```
It also no longer accepts expansions where a format string or argument has a "weird" proc macro span, that is one where the literal/expression it outputs has the span of one of its inputs. Kind of like a `format_args` specific `clippy_utils::is_from_proc_macro`, e.g. `format!(indoc! {" ... "})`
changelog: [`expect_fun_call`]: Fix suggestion for `format!` using captured variables
changelog: [`print_literal`], [`write_literal`], [`uninlined_format_args`]: Fix suggestion when following a comment including a comma
Fix and improve `match_type_on_diagnostic_item`
This extracts the fix for the lint out of #7647. There's still a couple of other functions to check, but at least this will get lint working again.
The two added util functions (`is_diagnostic_item` and `is_lang_item`) are needed to handle `DefId` for unit and tuple struct/variant constructors. The `rustc_diagnostic_item` and `lang` attributes are attached to the struct/variant `DefId`, but most of the time they are used through their constructors which have a different `DefId`. The two utility functions will check if the `DefId` is for a constructor and switch to the associated struct/variant `DefId`.
There does seem to be a bug on rustc's side where constructor `DefId`s from external crates seem to be returning `DefKind::Variant` instead of `DefKind::Ctor()`. There's a workaround put in right.
changelog: None
Remove unused `.fixed` files, only run asm_syntax doctests on x86
Two small changes, removes some unused `.fixed` and makes `clippy_lints` doctests pass on non x86 arches
changelog: none
* Check for `const`s and `static`s from external crates
* Check for `LangItem`s
* Handle inherent functions which have the same name as a field
* Also check the following functions:
* `match_trait_method`
* `match_def_path`
* `is_expr_path_def_path`
* `is_qpath_def_path`
* Handle checking for a constructor to a diagnostic item or `LangItem`
let unnecessary_cast work for trivial non_literal expressions
Signed-off-by: TennyZhuang <zty0826@gmail.com>
---
changelog: [`unnecessary_cast`]: fix for trivial non_literal expressions
Fixes#9562
[`unnecessary_cast`] add parenthesis when negative number uses a method
fix#9563
The issue was probably introduced by 90fe3bea52
changelog: [`unnecessary_cast`] add parenthesis when negative number uses a method
r? llogiq
use `is_integer_literal` more
I noticed that we have the `is_integer_literal` function in our `clippy_utils`, yet almost everywhere people still match int literal expressions manually. So I searched for instances to replace and shorten the code a bit.
---
changelog: none
Implement `manual_clamp` lint
Fixes#9477Fixes#6751
Identifies common patterns where usage of the `clamp` function would be more succinct and clear, and suggests using the `clamp` function instead.
changelog: [`manual_clamp`]: Implement manual_clamp lint
This lint detects calls to a `&self`-taking `as_ptr` method, where
the result is then immediately cast to a `*mut T`. Code like this
is probably invalid, as that pointer will not have write permissions,
and `*mut T` is usually used to write through.
Move lint level source explanation to the bottom
So, uhhhhh
r? `@estebank`
## User-facing change
"note: `#[warn(...)]` on by default" and such are moved to the bottom of the diagnostic:
```diff
- = note: `#[warn(unsupported_calling_conventions)]` on by default
= warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
= note: for more information, see issue #87678 <https://github.com/rust-lang/rust/issues/87678>
+ = note: `#[warn(unsupported_calling_conventions)]` on by default
```
Why warning is enabled is the least important thing, so it shouldn't be the first note the user reads, IMO.
## Developer-facing change
`struct_span_lint` and similar methods have a different signature.
Before: `..., impl for<'a> FnOnce(LintDiagnosticBuilder<'a, ()>)`
After: `..., impl Into<DiagnosticMessage>, impl for<'a, 'b> FnOnce(&'b mut DiagnosticBuilder<'a, ()>) -> &'b mut DiagnosticBuilder<'a, ()>`
The reason for this is that `struct_span_lint` needs to edit the diagnostic _after_ `decorate` closure is called. This also makes lint code a little bit nicer in my opinion.
Another option is to use `impl for<'a> FnOnce(LintDiagnosticBuilder<'a, ()>) -> DiagnosticBuilder<'a, ()>` altough I don't _really_ see reasons to do `let lint = lint.build(message)` everywhere.
## Subtle problem
By moving the message outside of the closure (that may not be called if the lint is disabled) `format!(...)` is executed earlier, possibly formatting `Ty` which may call a query that trims paths that crashes the compiler if there were no warnings...
I don't think it's that big of a deal, considering that we move from `format!(...)` to `fluent` (which is lazy by-default) anyway, however this required adding a workaround which is unfortunate.
## P.S.
I'm sorry, I do not how to make this PR smaller/easier to review. Changes to the lint API affect SO MUCH 😢
`Res::SelfTy` currently has two `Option`s. When the second one is `Some`
the first one is never consulted. So we can split it into two variants,
`Res::SelfTyParam` and `Res::SelfTyAlias`, reducing the size of `Res`
from 24 bytes to 12. This then shrinks `hir::Path` and
`hir::PathSegment`, which are the HIR types that take up the most space.
fix [`needless_borrow`], [`explicit_auto_deref`] FPs on unions
fix https://github.com/rust-lang/rust-clippy/issues/9383
changelog: fix [`needless_borrow`] false positive on unions
changelog: fix [`explicit_auto_deref`] false positive on unions
Left a couple debug derived impls on purpose I needed to debug as I don't think it's noise
Don't lint unstable moves in `std_instead_of_core`
Fixes#9515
changelog: [`std_instead_of_core`]: No longer suggests unstable modules such as `core::error`
add `box-default` lint
This adds a `box-default` lint to suggest using `Box::default()` instead of `Box::new(Default::default())`, which offers less moving parts and potentially better performance according to [the perf book](https://nnethercote.github.io/perf-book/standard-library-types.html#box).
---
changelog: add [`box_default`] lint
[`needless_return`] Recursively remove unneeded semicolons
fix#8336,
fix#8156,
fix https://github.com/rust-lang/rust-clippy/issues/7358,
fix#9192,
fix https://github.com/rust-lang/rust-clippy/issues/9503
changelog: [`needless_return`] Recursively remove unneeded semicolons
For now the suggestion about removing the semicolons are hidden because they would be very noisy and should be obvious if the user wants to apply the lint manually instead of using `--fix`. This could be an issue for beginner, but haven't found better way to display it.
[arithmetic-side-effects] Consider references
Takes into consideration integer references like `&i32::MAX` because currently things like `let _ = &1 + 0` trigger the lint.
changelog: FP: [`arithmetic_side_effects`]: Now ignores references
[9507](https://github.com/rust-lang/rust-clippy/pull/9507)
Don't lint `*_interior_mutable_const` on unions due to potential ICE.
fixes#9445
cc rust-lang/rust#101113
This started ICE'ing sometime last month due to stricter UB checks. I'm not sure how we could check the value of a union as MIRI doesn't seem to store which field is currently active.
changelog: Don't ICE on const unions containing a `!Freeze` type.
Silence [`question_mark`] in const context
fix https://github.com/rust-lang/rust-clippy/issues/9175
When `const_try` is stabilised can be turned into a MSRV
changelog: Silence [`question_mark`] in const context
Implement https://github.com/rust-lang/rust-clippy/issues/8368 - a new
lint to inline format arguments such as `print!("{}", var)` into
`print!("{var}")`.
code | suggestion | comment
---|---|---
`print!("{}", var)` | `print!("{var}")` | simple variables
`print!("{0}", var)` | `print!("{var}")` | positional variables
`print!("{v}", v=var)` | `print!("{var}")` | named variables
`print!("{0} {0}", var)` | `print!("{var} {var}")` | aliased variables
`print!("{0:1$}", var, width)` | `print!("{var:width$}")` | width
support
`print!("{0:.1$}", var, prec)` | `print!("{var:.prec$}")` | precision
support
`print!("{:.*}", prec, var)` | `print!("{var:.prec$}")` | asterisk
support
code | suggestion | comment
---|---|---
`print!("{0}={1}", var, 1+2)` | `print!("{var}={0}", 1+2)` | Format
string uses an indexed argument that cannot be inlined. Supporting this
case requires re-indexing of the format string.
changelog: [`uninlined_format_args`]: A new lint to inline format
arguments, i.e. `print!("{}", var)` into `print!("{var}")`
fix a ui test
use `into`
fix clippy ui test
fix a run-make-fulldeps test
implement `IntoQueryParam<DefId>` for `OwnerId`
use `OwnerId` for more queries
change the type of `ParentOwnerIterator::Item` to `(OwnerId, OwnerNode)`
[`never_loop`]: Fix FP with let..else statements.
Fixes#9356
This has been bugging me for a while, so I thought I'd take a stab at it! I'm completely uncertain about the quality of my code, but I think it's an alright start, so opening this PR to get some feedback from more experienced clippy people :)
changelog: [`never_loop`]: Fix FP with let..else statements
Introduce mir::Unevaluated
Previously the distinction between unevaluated constants in the type-system and in mir was not explicit and a little confusing. Probably better to introduce its own type for that.
r? `@lcnr`
Changelog for Rust 1.64 🍎
The normal release preparation dance. I've written the changelog like the version has already been released. The PR can be approved and then merged by anyone after the release of Rust 1.64 🙃
---
changelog: none
Fixes#9504
Compiler generated call `into_iter` nodes return empty substs
which we need when checking it's predicates. Handle this by
simply exitting when we encounter one. This change introduces
false negatives in place of the ICEs.
[arithmetic-side-effects] Finish non-overflowing ops
Extends https://github.com/rust-lang/rust-clippy/pull/9474 to also take into consideration "raw" binary operations. For example, `let a = b / 2` and `let a = 1 * b` won't trigger the lint.
changelog: [arithmetic-side-effects] Finish non-overflowing ops
Clippy pre beta branch fix
Before beta is branched on Friday, I want to move the `unused_peekable` lint that was added in this release cycle (1.65) to `nursery`. This lint was already reported twice (https://github.com/rust-lang/rust-clippy/issues/9456, https://github.com/rust-lang/rust-clippy/issues/9462) in a short time, so it is probably a good idea to fix it before it hits beta and then stable.
r? `@Manishearth`
Make module-style lints resilient to --remap-path-prefix
changelog: [`self_named_module_files`], [`mod_module_files`]: Make module-style lints resilient to `--remap-path-prefix`
Without this if a user has configured `--remap-path-prefix` to be used for a prefix containing the current source directory the lints would silently fail to generate a warning.
Initial implementation of dyn*
This PR adds extremely basic and incomplete support for [dyn*](https://smallcultfollowing.com/babysteps//blog/2022/03/29/dyn-can-we-make-dyn-sized/). The goal is to get something in tree behind a flag to make collaboration easier, and also to make sure the implementation so far is not unreasonable. This PR does quite a few things:
* Introduce `dyn_star` feature flag
* Adds parsing for `dyn* Trait` types
* Defines `dyn* Trait` as a sized type
* Adds support for explicit casts, like `42usize as dyn* Debug`
* Including const evaluation of such casts
* Adds codegen for drop glue so things are cleaned up properly when a `dyn* Trait` object goes out of scope
* Adds codegen for method calls, at least for methods that take `&self`
Quite a bit is still missing, but this gives us a starting point. Note that this is never intended to become stable surface syntax for Rust, but rather `dyn*` is planned to be used as an implementation detail for async functions in dyn traits.
Joint work with `@nikomatsakis` and `@compiler-errors.`
r? `@bjorn3`
Migrate write.rs to a late pass
changelog: Migrates write.rs from a pre expansion pass to a late pass
changelog: [`positional_named_format_parameters`] is renamed in favour of the rustc lint `named_arguments_used_positionally`
- Macros are now identified by diagnostic items, so will no longer lint user defined macros named, e.g. a custom `print!`
- `print_literal`/`write_literal` no longer lint no longer lint literals that come from macro expansions, e.g. `env!("FOO")`
- `print_with_newline`/`write_with_newline` no longer lint strings with any internal `\r` or `\n`s
~~A false negative, `print_literal`/`write_literal` don't lint format strings that produce `FormatSpec`s, e.g. ones containing pretty print/width/align specifiers~~
Suggestion changes:
- ~~`print_literal`/`write_literal` no longer have suggestions, as the spans for the `{}`s were not easily obtainable~~
- `print_with_newline`/`write_with_newline` has a better suggestion for a sole literal newline, but no longer has suggestions for len > 1 strings that end in a literal newline
- ~~`use_debug` spans are less precise, now point to the whole format string~~
The diff for write.rs is pretty unwieldy, other than for the `declare_clippy_lint!`s I think you'd be better off viewing it as a brand new file rather than looking at the diff, as it's mostly written from scratch
cc #6610, fixes#5721, fixes#7195, fixes#8615
Fix `unused_peekable` closure and `f(&mut peekable)` false positives
changelog: Fix [`unused_peekable`] false positive when peeked in a closure or called as `f(&mut peekable)`
The `return`/`break` changes aren't part of the fix, they allow an earlier return in some cases. `break` is replaced with `return` for style purposes as they do the same thing in this case
Fixes#9456Fixes#9462
Use `DisplayBuffer` for socket addresses.
Continuation of https://github.com/rust-lang/rust/pull/100625 for socket addresses.
Renames `net::addr` to `net::addr::socket`, `net::ip` to `net::addr::ip` and `net::ip::display_buffer::IpDisplayBuffer` to `net::addr::display_buffer::DisplayBuffer`.
Fix `range_{plus,minus}_one` bad suggestions
Fixes#9431.
The current `range_plus_one` and `range_minus_one` suggestions are completely incorrect when macros are involved.
This commit resolves this by disabling the lints for any range expression that is expanded from a macro. The reasons for this are that it is very difficult to create a correct suggestion in this case and that false negatives are less important for pedantic lints.
changelog: Fix `range_{plus,minus}_one` bad suggestions
Fixes#9431.
The current `range_plus_one` and `range_minus_one` suggestions
are completely incorrect when macros are involved.
This commit resolves this by disabling the lints for any range
expression that is expanded from a macro. The reasons for this
are that it is very difficult to create a correct suggestion in
this case and that false negatives are less important for
pedantic lints.
Rollup of 7 pull requests
Successful merges:
- #98933 (Opaque types' generic params do not imply anything about their hidden type's lifetimes)
- #101041 (translations(rustc_session): migrates rustc_session to use SessionDiagnostic - Pt. 2)
- #101424 (Adjust and slightly generalize operator error suggestion)
- #101496 (Allow lower_lifetime_binder receive a closure)
- #101501 (Allow lint passes to be bound by `TyCtxt`)
- #101515 (Recover from typo where == is used in place of =)
- #101545 (Remove unnecessary `PartialOrd` and `Ord`)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
Allow lint passes to be bound by `TyCtxt`
This will allow storing things like `Ty<'tcx>` inside late lint passes. It's already possible to store various id types so they're already implicitly bound to a specific `TyCtxt`.
r? rust-lang/compiler
rustc: Parameterize `ty::Visibility` over used ID
It allows using `LocalDefId` instead of `DefId` when possible, and also encode cheaper `Visibility<DefIndex>` into metadata.
[Arithmetic] Consider literals
Fixes https://github.com/rust-lang/rust-clippy/issues/9307 and makes the `arithmetic` lint behave like `integer_arithmetic`.
It is worth noting that literal integers of a binary operation (`1 + 1`, `i32::MAX + 1`), **regardless if they are in a constant environment**, won't trigger the lint. Assign operations also have similar reasoning.
changelog: Consider literals in the arithmetic lint
Suggest `unwrap_or_default` when closure returns `"".to_string`
Closes https://github.com/rust-lang/rust-clippy/issues/9420
changelog: [`unwrap_or_else_default`]: suggest `unwrap_or_default()` instead of `unwrap_or_else` with a closure that returns an empty `to_string`.
`BindingAnnotation` refactor
* `ast::BindingMode` is deleted and replaced with `hir::BindingAnnotation` (which is moved to `ast`)
* `BindingAnnotation` is changed from an enum to a tuple struct e.g. `BindingAnnotation(ByRef::No, Mutability::Mut)`
* Associated constants added for convenience `BindingAnnotation::{NONE, REF, MUT, REF_MUT}`
One goal is to make it more clear that `BindingAnnotation` merely represents syntax `ref mut` and not the actual binding mode. This was especially confusing since we had `ast::BindingMode`->`hir::BindingAnnotation`->`thir::BindingMode`.
I wish there were more symmetry between `ByRef` and `Mutability` (variant) naming (maybe `Mutable::Yes`?), and I also don't love how long the name `BindingAnnotation` is, but this seems like the best compromise. Ideas welcome.
Unlike past similar work done in #6228, expand the existing `or_fun_call`
lint to detect `or_insert` calls with a `T::new()` or `T::default()`
argument, much like currently done for `unwrap_or` calls. In that case,
suggest the use of `or_default`, which is more idiomatic.
Note that even with this change, `or_insert_with(T::default)` calls
aren't detected as candidates for `or_default()`, in the same manner
that currently `unwrap_or_else(T::default)` calls aren't detected as
candidates for `unwrap_or_default()`.
Also, as a nearby cleanup, change `KNOW_TYPES` from `static` to `const`,
since as far as I understand it's preferred (should Clippy have a lint
for that?).
Fixes#3812.
fix wording for `derivable_impls`
While looking at the explanation as to why this lint was not automatically applicable, found the explanation a bit clunky grammatically.
Feel free to close if you consider the wording was correct in the first place.
changelog: none
Fixes#9351.
Note that this commit reworks that fix for #9317. The change
is to check that the type implements `AsRef<str>` before regarding
`to_string` as an equivalent of `to_owned`. This was suggested
by Jarcho in the #9317 issue comments.
The benefit of this is that it moves some complexity out of
`check_other_call_arg` and simplifies the module as a whole.
Fix `mut_mutex_lock` when Mutex is behind immutable deref
I *think* the problem here is the `if let ty::Ref(_, _, Mutability::Mut) = cx.typeck_results().expr_ty(recv).kind()` line tries to check if the `Mutex` can be mutably borrowed (there already is a test for `Arc<Mutex<_>>`), but gets bamboozled by the `&mut Arc` indirection. And I *think* checking the deref-adjustment to filter immutable-adjust (the deref through the `Arc`, starting from `&mut Arc`) is the correct fix.
Fixes#9415
changelog: Fix `mut_mutex_lock` when Mutex is behind immutable deref
Don't use `hir_ty_to_ty` in `result_large_err`
fixes#9414
This occurs starting with 2022-09-01. I checked that this does fix the ICE on rust-lang/rust@9353538. Not sure which pr caused the late-bound region to leak through `hir_ty_to_ty`.
changelog: None
Fix `suboptimal_float` not linting on `{const}.powf({const})`
There used to be an early return if the receiver was an effective const but the method was not linted, not taking into account later cases where the receiver and the arguments are both effective consts for different methods. Removed the early return.
Fixes#9402Fixes#9201
changelog: Fix `suboptimal_flops`, `imprecise_flops` not linting on `{const}.powf({const})` et al
Fix the emission order of `trait_duplication_in_bounds`
Makes the lint emit in source order rather than whatever order the hash map happens to be in. This is currently blocking the sync into rustc.
changelog: None
Fix missing parens in `suboptimal_flops` suggestion
Fixes#9391. The problem is simple enough, I didn't check if the same problem occurs elsewhere, though.
changelog: fix missing parenthesis in `suboptimal_flops` suggestion
Ignore `match_like_matches_macro` when there is comment
Closes#9164
changelog: [`match_like_matches_macro`] is ignored when there is some comment inside the match block.
Also add `span_contains_comment` util to check if given span contains comments.
Implemented `suspicious_to_owned` lint to check if `to_owned` is called on a `Cow`
changelog: Add lint ``[`suspicious_to_owned`]``
-----------------
Hi,
posting this unsolicited PR as I've been burned by this issue :)
Being unsolicited, feel free to reject it or reassign a different lint level etc.
This lint checks whether `to_owned` is called on `Cow<'_, _>`. This is done because `to_owned` is very similarly named to `into_owned`, but the effect of calling those two methods is completely different (one makes the `Cow::Borrowed` into a `Cow::Owned`, the other just clones the `Cow`). If the cow is then passed to code for which the type is not checked (e.g. generics, closures, etc.) it might slip through and if the cow data is coming from an unsafe context there is the potential for accidentally cause undefined behavior.
Even if not falling into this painful case, there's really no reason to call `to_owned` on a `Cow` other than confusing people reading the code: either `into_owned` or `clone` should be called.
Note that this overlaps perfectly with `implicit_clone` as a warning, but `implicit_clone` is classified pedantic (while the consequences for `Cow` might be of a wider blast radius than just pedantry); given the overlap, I set-up the lint so that if `suspicious_to_owned` triggers `implicit_clone` will not trigger. I'm not 100% sure this is done in the correct way (I tried to copy what other lints were doing) so please provide feedback on it if it isn't.
### Checklist
- \[x] Followed [lint naming conventions][lint_naming]
- \[x] Added passing UI tests (including committed `.stderr` file)
- \[x] `cargo test` passes locally
- \[x] Executed `cargo dev update_lints`
- \[x] Added lint documentation
- \[x] Run `cargo dev fmt`
This is done because `to_owned` is very similarly named to `into_owned`, but the
effect of calling those two methods is completely different. This creates
confusion (stemming from the ambiguity of the 'owned' term in the context of
`Cow`s) and might not be what the writer intended.
new lint
This fixes#6576
If you added a new lint, here's a checklist for things that will be
checked during review or continuous integration.
- \[x] Followed [lint naming conventions][lint_naming]
- \[x] Added passing UI tests (including committed `.stderr` file)
- \[x] `cargo test` passes locally
- \[x] Executed `cargo dev update_lints`
- \[x] Added lint documentation
- \[x] Run `cargo dev fmt`
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changelog: add [`multi_assignments`] lint
