E0277 causes syntax error when adding several bounds at the same time via several errors

[matthiaskrgr]

Code

#![feature(associated_type_defaults)]

use std::{
    fmt::Display,
    ops::{AddAssign, Deref},
};

trait UncheckedCopy: Sized + std::fmt::Display + AddAssign<&'static str> + Deref + Copy {
    // This Output is said to be Copy. Yet we default to Self
    // and it's accepted, not knowing if Self ineed is Copy
    type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    //~^ ERROR the trait bound `Self: Copy` is not satisfied
    //~| ERROR the trait bound `Self: Deref` is not satisfied
    //~| ERROR cannot add-assign `&'static str` to `Self`
    //~| ERROR `Self` doesn't implement `std::fmt::Display`

    // We said the Output type was Copy, so we can Copy it freely!
    fn unchecked_copy(other: &Self::Output) -> Self::Output {
        (*other)
    }

    fn make_origin(s: Self) -> Self::Output {
        s.into()
    }
}

impl<T> UncheckedCopy for T {}

fn bug<T: UncheckedCopy>(origin: T) {
    let origin = T::make_origin(origin);
    let mut copy = T::unchecked_copy(&origin);

    // assert we indeed have 2 strings pointing to the same buffer.
    assert_eq!(origin.as_ptr(), copy.as_ptr());

    // Drop the origin. Any use of `copy` is UB.
    drop(origin);

    copy += "This is invalid!";
    println!("{}", copy);
}

fn main() {
    bug(String::from("hello!"));
}

Current output

warning: unnecessary parentheses around block return value
  --> src/lib.rs:19:9
   |
19 |         (*other)
   |         ^      ^
   |
   = note: `#[warn(unused_parens)]` on by default
help: remove these parentheses
   |
19 -         (*other)
19 +         *other
   |

error[E0277]: the trait bound `T: Copy` is not satisfied
  --> src/lib.rs:27:27
   |
27 | impl<T> UncheckedCopy for T {}
   |                           ^ the trait `Copy` is not implemented for `T`
   |
note: required by a bound in `UncheckedCopy`
  --> src/lib.rs:8:84
   |
8  | trait UncheckedCopy: Sized + std::fmt::Display + AddAssign<&'static str> + Deref + Copy {
   |                                                                                    ^^^^ required by this bound in `UncheckedCopy`
help: consider restricting type parameter `T`
   |
27 | impl<T: std::marker::Copy> UncheckedCopy for T {}
   |       +++++++++++++++++++

error[E0277]: the trait bound `T: Deref` is not satisfied
  --> src/lib.rs:27:27
   |
27 | impl<T> UncheckedCopy for T {}
   |                           ^ the trait `Deref` is not implemented for `T`
   |
note: required by a bound in `UncheckedCopy`
  --> src/lib.rs:8:76
   |
8  | trait UncheckedCopy: Sized + std::fmt::Display + AddAssign<&'static str> + Deref + Copy {
   |                                                                            ^^^^^ required by this bound in `UncheckedCopy`
help: consider restricting type parameter `T`
   |
27 | impl<T: std::ops::Deref> UncheckedCopy for T {}
   |       +++++++++++++++++

error[E0277]: cannot add-assign `&'static str` to `T`
  --> src/lib.rs:27:27
   |
27 | impl<T> UncheckedCopy for T {}
   |                           ^ no implementation for `T += &'static str`
   |
note: required by a bound in `UncheckedCopy`
  --> src/lib.rs:8:50
   |
8  | trait UncheckedCopy: Sized + std::fmt::Display + AddAssign<&'static str> + Deref + Copy {
   |                                                  ^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `UncheckedCopy`
help: consider restricting type parameter `T`
   |
27 | impl<T: std::ops::AddAssign<&'static str>> UncheckedCopy for T {}
   |       +++++++++++++++++++++++++++++++++++

error[E0277]: `T` doesn't implement `std::fmt::Display`
  --> src/lib.rs:27:27
   |
27 | impl<T> UncheckedCopy for T {}
   |                           ^ `T` cannot be formatted with the default formatter
   |
   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
note: required by a bound in `UncheckedCopy`
  --> src/lib.rs:8:30
   |
8  | trait UncheckedCopy: Sized + std::fmt::Display + AddAssign<&'static str> + Deref + Copy {
   |                              ^^^^^^^^^^^^^^^^^ required by this bound in `UncheckedCopy`
help: consider restricting type parameter `T`
   |
27 | impl<T: std::fmt::Display> UncheckedCopy for T {}
   |       +++++++++++++++++++

For more information about this error, try `rustc --explain E0277`.

Here we have several errors trying to add bounds to impl<T> UncheckedCopy for T {}.

help: consider restricting type parameter `T`
   |
27 | impl<T: std::marker::Copy> UncheckedCopy for T {}

This would work when adding only a single bound, but here we end up adding several bounds, separated by : which causes syntax error, the "fully fixed" code ends up being
impl<T: std::marker::Copy: std::ops::Deref: std::ops::AddAssign<&'static str>: std::fmt::Display> UncheckedCopy for T {}

Can we make rust clever enough to separate these by + ?

[estebank]

Under the current machinery this will be difficult to accomplish, specially in general. The best option we have available to us (beyond more advance tracking for suggestions where we don't represent them as span+string tuples but rather make them carry semantic information, like "add param to this node") would be to try and group up E0277 errors with the same root obligation into a single one, in a similar way we do for E0599.