Rust error E0195: lifetime parameters do not match the trait definition

What rustc prints

error[E0195]: lifetime parameters do not match the trait definition
 --> main.rs:8:12
  |
8 |     fn bar<'a,'b>(x: &'a str, y: &'b str) {
  |            ^^ ^^
  |
  = note: lifetime parameters differ in whether they are early- or late-bound
note: `'a` differs between the trait and impl
 --> main.rs:2:12
  |
1 | trait Trait {
  | ----------- in this trait...
2 |     fn bar<'a,'b:'a>(x: &'a str, y: &'b str);
  |            ^^    -- this lifetime bound makes `'a` early-bound
  |            |
  |            `'a` is early-bound
...
7 | impl Trait for Foo {
  | ------------------ in this impl...
8 |     fn bar<'a,'b>(x: &'a str, y: &'b str) {
  |            ^^ `'a` is late-bound
note: `'b` differs between the trait and impl
 --> main.rs:2:15
  |
1 | trait Trait {
  | ----------- in this trait...
2 |     fn bar<'a,'b:'a>(x: &'a str, y: &'b str);
  |               ^^ -- this lifetime bound makes `'b` early-bound
  |               |
  |               `'b` is early-bound
...
7 | impl Trait for Foo {
  | ------------------ in this impl...
8 |     fn bar<'a,'b>(x: &'a str, y: &'b str) {
  |               ^^ `'b` is late-bound

Real output of rustc 1.99.0 compiling the official example below (2021 edition). Your names and line numbers will differ; the first line is the part to match.

trait Trait {
    fn bar<'a,'b:'a>(x: &'a str, y: &'b str);
}

struct Foo;

impl Trait for Foo {
    fn bar<'a,'b>(x: &'a str, y: &'b str) {
    // error: lifetime parameters or bounds on method `bar`
    // do not match the trait declaration
    }
}

trait Trait {
    fn t<'a,'b:'a>(x: &'a str, y: &'b str);
}

struct Foo;

impl Trait for Foo {
    fn t<'a,'b:'a>(x: &'a str, y: &'b str) { // ok!
    }
}

Related errors

• E0382borrow of moved value
• E0499cannot borrow as mutable more than once at a time
• E0502cannot borrow as mutable because it is also borrowed as immutable
• E0106missing lifetime specifier
• E0161cannot move a value of type `dyn Bar`
• E0207the type parameter `T` is not constrained by the impl trait, self type, or predicates
• E0226only a single explicit lifetime bound is permitted

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