error: expected one of `,` or `>`, found `;`
  --> $DIR/lifetime-semicolon.rs:7:31
   |
LL | fn foo<'a, 'b>(_x: &mut Foo<'a; 'b>) {}
   |                               ^ expected one of `,` or `>`
   |
help: use a comma to separate type parameters
   |
LL | fn foo<'a, 'b>(_x: &mut Foo<'a, 'b>) {}
   |                               ~

error: aborting due to previous error