Static rustc_lint::builtin::TRIVIAL_BOUNDS

static TRIVIAL_BOUNDS: &Lint

The trivial_bounds lint detects trait bounds that don’t depend on any type parameters.

Example

#![feature(trivial_bounds)]
pub struct A where i32: Copy;

{{produces}}

Explanation

Usually you would not write a trait bound that you know is always true, or never true. However, when using macros, the macro may not know whether or not the constraint would hold or not at the time when generating the code. Currently, the compiler does not alert you if the constraint is always true, and generates an error if it is never true. The trivial_bounds feature changes this to be a warning in both cases, giving macros more freedom and flexibility to generate code, while still providing a signal when writing non-macro code that something is amiss.

See RFC 2056 for more details. This feature is currently only available on the nightly channel, see tracking issue #48214.