error[E0053]: method `from` has an incompatible type for trait --> $DIR/issue-90444.rs:3:16 | LL | fn from(_: fn((), (), &mut ())) -> Self { | ^^^^^^^^^^^^^^^^^^^ | | | types differ in mutability | help: change the parameter type to match the trait: `for<'r> fn((), (), &'r ())` | = note: expected fn pointer `fn(for<'r> fn((), (), &'r ())) -> A` found fn pointer `fn(for<'r> fn((), (), &'r mut ())) -> A` error[E0053]: method `from` has an incompatible type for trait --> $DIR/issue-90444.rs:11:16 | LL | fn from(_: fn((), (), u64)) -> Self { | ^^^^^^^^^^^^^^^ | | | expected `u32`, found `u64` | help: change the parameter type to match the trait: `fn((), (), u32)` | = note: expected fn pointer `fn(fn((), (), u32)) -> B` found fn pointer `fn(fn((), (), u64)) -> B` error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0053`.