Deny-by-default lints

These lints are all set to the 'deny' level by default.

exceeding-bitshifts

This lint detects that a shift exceeds the type's number of bits. Some example code that triggers this lint:

1_i32 << 32;

This will produce:

error: bitshift exceeds the type's number of bits
 --> src/main.rs:2:5
  |
2 |     1_i32 << 32;
  |     ^^^^^^^^^^^
  |

invalid-type-param-default

This lint detects type parameter default erroneously allowed in invalid location. Some example code that triggers this lint:

fn foo<T=i32>(t: T) {}

This will produce:

error: defaults for type parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions.
 --> src/main.rs:4:8
  |
4 | fn foo<T=i32>(t: T) {}
  |        ^
  |
  = note: `#[deny(invalid_type_param_default)]` 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 #36887 <https://github.com/rust-lang/rust/issues/36887>

missing-fragment-specifier

The missing_fragment_specifier warning is issued when an unused pattern in a macro_rules! macro definition has a meta-variable (e.g. $e) that is not followed by a fragment specifier (e.g. :expr).

This warning can always be fixed by removing the unused pattern in the macro_rules! macro definition.

mutable-transmutes

This lint catches transmuting from &T to &mut T because it is undefined behavior. Some example code that triggers this lint:

unsafe {
    let y = std::mem::transmute::<&i32, &mut i32>(&5);
}

This will produce:

error: mutating transmuted &mut T from &T may cause undefined behavior, consider instead using an UnsafeCell
 --> src/main.rs:3:17
  |
3 |         let y = std::mem::transmute::<&i32, &mut i32>(&5);
  |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |

no-mangle-const-items

This lint detects any const items with the #[no_mangle] attribute. Constants do not have their symbols exported, and therefore, this probably means you meant to use a static, not a const. Some example code that triggers this lint:

#[no_mangle]
const FOO: i32 = 5;

This will produce:

error: const items should never be `#[no_mangle]`
 --> src/main.rs:3:1
  |
3 | const FOO: i32 = 5;
  | -----^^^^^^^^^^^^^^
  | |
  | help: try a static value: `pub static`
  |

overflowing-literals

This lint detects literal out of range for its type. Some example code that triggers this lint:


#![allow(unused_variables)]
fn main() {
let x: u8 = 1000;
}

This will produce:

error: literal out of range for u8
 --> src/main.rs:2:17
  |
2 |     let x: u8 = 1000;
  |                 ^^^^
  |

patterns-in-fns-without-body

This lint detects patterns in functions without body were that were previously erroneously allowed. Some example code that triggers this lint:


#![allow(unused_variables)]
fn main() {
trait Trait {
    fn foo(mut arg: u8);
}
}

This will produce:

warning: patterns aren't allowed in methods without bodies
 --> src/main.rs:2:12
  |
2 |     fn foo(mut arg: u8);
  |            ^^^^^^^
  |
  = note: `#[warn(patterns_in_fns_without_body)]` 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 #35203 <https://github.com/rust-lang/rust/issues/35203>

To fix this, remove the pattern; it can be used in the implementation without being used in the definition. That is:


#![allow(unused_variables)]
fn main() {
trait Trait {
    fn foo(arg: u8);
}

impl Trait for i32 {
    fn foo(mut arg: u8) {

    }
}
}

pub-use-of-private-extern-crate

This lint detects a specific situation of re-exporting a private extern crate;

unknown-crate-types

This lint detects an unknown crate type found in a #[crate_type] directive. Some example code that triggers this lint:

#![crate_type="lol"]

This will produce:

error: invalid `crate_type` value
 --> src/lib.rs:1:1
  |
1 | #![crate_type="lol"]
  | ^^^^^^^^^^^^^^^^^^^^
  |

const-err

This lint detects expressions that will always panic at runtime and would be an error in a const context.

let _ = [0; 4][4];

This will produce:

error: index out of bounds: the len is 4 but the index is 4
 --> src/lib.rs:1:9
  |
1 | let _ = [0; 4][4];
  |         ^^^^^^^^^
  |

order-dependent-trait-objects

This lint detects a trait coherency violation that would allow creating two trait impls for the same dynamic trait object involving marker traits.