mirror of
https://github.com/rust-lang/rust-clippy
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100 lines
5.3 KiB
Markdown
100 lines
5.3 KiB
Markdown
#rust-clippy
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[](https://travis-ci.org/Manishearth/rust-clippy)
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A collection of lints that give helpful tips to newbies and catch oversights.
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##Lints
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Lints included in this crate:
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- `single_match`: Warns when a match statement with a single nontrivial arm (i.e, where the other arm is `_ => {}`) is used, and recommends `if let` instead.
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- `box_vec`: Warns on usage of `Box<Vec<T>>`
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- `linkedlist`: Warns on usage of `LinkedList`
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- `str_to_string`: Warns on usage of `str::to_string()`
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- `toplevel_ref_arg`: Warns when a function argument is declared `ref` (i.e. `fn foo(ref x: u8)`, but not `fn foo((ref x, ref y): (u8, u8))`)
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- `eq_op`: Warns on equal operands on both sides of a comparison or bitwise combination
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- `bad_bit_mask`: Denies expressions of the form `_ & mask == select` that will only ever return `true` or `false` (because in the example `select` containing bits that `mask` doesn't have)
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- `ineffective_bit_mask`: Warns on expressions where a bit mask will be rendered useless by a comparison, e.g. `(x | 1) > 2`
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- `needless_bool` : Warns on if-statements with plain booleans in the then- and else-clause, e.g. `if p { true } else { false }`
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- `ptr_arg`: Warns on fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` instead, respectively
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- `approx_constant`: Warns if the approximate of a known float constant (in `std::f64::consts` or `std::f32::consts`) is found and suggests to use the constant
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- `cmp_nan`: Denies comparisons to NAN (which will always return false, which is probably not intended)
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- `float_cmp`: Warns on `==` or `!=` comparisons of floaty typed values. As floating-point operations usually involve rounding errors, it is always better to check for approximate equality within some small bounds
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- `precedence`: Warns on expressions where precedence may trip up the unwary reader of the source and suggests adding parenthesis, e.g. `x << 2 + y` will be parsed as `x << (2 + y)`
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- `redundant_closure`: Warns on usage of eta-reducible closures like `|a| foo(a)` (which can be written as just `foo`)
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- `identity_op`: Warns on identity operations like `x + 0` or `y / 1` (which can be reduced to `x` and `y`, respectively)
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- `mut_mut`: Warns on `&mut &mut` which is either a copy'n'paste error, or shows a fundamental misunderstanding of references
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- `len_zero`: Warns on `_.len() == 0` and suggests using `_.is_empty()` (or similar comparisons with `>` or `!=`)
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- `len_without_is_empty`: Warns on traits or impls that have a `.len()` but no `.is_empty()` method
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- `cmp_owned`: Warns on creating owned instances for comparing with others, e.g. `x == "foo".to_string()`
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- `inline_always`: Warns on `#[inline(always)]`, because in most cases it is a bad idea
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- `collapsible_if`: Warns on cases where two nested `if`-expressions can be collapsed into one, e.g. `if x { if y { foo() } }` can be written as `if x && y { foo() }`
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- `zero_width_space`: Warns on encountering a unicode zero-width space
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- `string_add_assign`: Warns on `x = x + ..` where `x` is a `String` and suggests using `push_str(..)` instead.
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- `needless_return`: Warns on using `return expr;` when a simple `expr` would suffice.
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- `let_and_return`: Warns on doing `let x = expr; x` at the end of a function.
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- `option_unwrap_used`: Warns when `Option.unwrap()` is used, and suggests `.expect()`.
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- `result_unwrap_used`: Warns when `Result.unwrap()` is used (silent by default).
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- `modulo_one`: Warns on taking a number modulo 1, which always has a result of 0.
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To use, add the following lines to your Cargo.toml:
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```
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[dependencies]
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clippy = "*"
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```
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More to come, please [file an issue](https://github.com/Manishearth/rust-clippy/issues) if you have ideas!
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##Usage
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Compiler plugins are highly unstable and will only work with a nightly Rust for now. Since stable Rust is backwards compatible, you should be able to compile your stable programs with nightly Rust with clippy plugged in to circumvent this.
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Add in your `Cargo.toml`:
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```toml
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[dependencies.clippy]
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git = "https://github.com/Manishearth/rust-clippy"
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```
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Sample `main.rs`:
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```rust
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#![feature(plugin)]
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#![plugin(clippy)]
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fn main(){
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let x = Some(1u8);
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match x {
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Some(y) => println!("{:?}", y),
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_ => ()
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}
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}
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```
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Produce this warning:
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```
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src/main.rs:8:5: 11:6 warning: You seem to be trying to use match for destructuring a single type. Did you mean to use `if let`?, #[warn(single_match)] on by default
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src/main.rs:8 match x {
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src/main.rs:9 Some(y) => println!("{:?}", y),
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src/main.rs:10 _ => ()
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src/main.rs:11 }
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src/main.rs:8:5: 11:6 help: Try
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if let Some(y) = x { println!("{:?}", y) }
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```
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You can add options to `allow`/`warn`/`deny`:
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- the whole set using the `clippy` lint group (`#![deny(clippy)]`, etc)
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- only some lints (`#![deny(single_match, box_vec)]`, etc)
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- `allow`/`warn`/`deny` can be limited to a single function or module using `#[allow(...)]`, etc
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Note: `deny` produces errors instead of warnings
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To have cargo compile your crate with clippy without needing `#![plugin(clippy)]`
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in your code, you can use:
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```
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cargo rustc -- -L /path/to/clippy_so -Z extra-plugins=clippy
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```
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##License
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Licensed under [MPL](https://www.mozilla.org/MPL/2.0/). If you're having issues with the license, let me know and I'll try to change it to something more permissive.
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