Show error E0277 when the trait bound of a struct's member's type is unsatisfied even if E0204 is also present

[john01dav]

Given the following code: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=fbd47fd0a07c3a9a05978696f46aac3d

use std::fmt::Debug;

#[derive(Debug, Copy, Clone)]
pub struct Vector2<T: Debug + Copy + Clone>{
    pub x: T,
    pub y: T
}

#[derive(Debug, Copy, Clone)]
pub struct AABB<T>{
    pub loc: Vector2<T>,
    pub size: Vector2<T>
}

The current output is:

error[E0204]: the trait `Copy` may not be implemented for this type
  --> src/main.rs:10:17
   |
10 | #[derive(Debug, Copy, Clone)]
   |                 ^^^^
11 | pub struct AABB<T>{
12 |     pub loc: Vector2<T>,
   |     ------------------- this field does not implement `Copy`
13 |     pub size: Vector2<T>
   |     -------------------- this field does not implement `Copy`
   |
   = note: this error originates in the derive macro `Copy` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0204`.

Ideally the output should look like:

Keeping the other error may or may not make sense, but I propose adding this, as it points more towards how to fix the issue and prevents barking up the tree of how a derive(Copy)'d type can not implement copy (there's a good answer here, but it was not immediately obvious to me upon seeing the original error).

I generated this error message by removing the derive line from the AABB struct.

error[E0277]: the trait bound `T: Copy` is not satisfied
  --> src/lib.rs:10:14
   |
4  | pub struct Vector2<T: Debug + Copy + Clone>{
   |                               ---- required by this bound in `Vector2`
...
10 |     pub loc: Vector2<T>,
   |              ^^^^^^^^^^ the trait `Copy` is not implemented for `T`
   |
help: consider restricting type parameter `T`
   |
9  | pub struct AABB<T: std::marker::Copy>{
   |                  ^^^^^^^^^^^^^^^^^^^

For more information about this error, try `rustc --explain E0277`.
error: could not compile `playground` due to 2 previous errors

This bug takes place on beta and nightly according to the Rust playground.

[rodrimati1992]

This bug takes place on beta and nightly according to the Rust playground.

That's the exact error from Rust 1.43.0 onward, before that it doesn't say what derive the error comes from.
Just clarifying that this is not a recent change.

[compiler-errors]

The error has gotten (slightly) better on nightly since a recent change of mine:

error[[E0204]](https://doc.rust-lang.org/nightly/error-index.html#E0204): the trait `Copy` may not be implemented for this type
  [--> src/lib.rs:9:17
](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018#)   |
9  | #[derive(Debug, Copy, Clone)]
   |                 ^^^^
10 | pub struct AABB<T>{
11 |     pub loc: Vector2<T>,
   |     ------------------- this field does not implement `Copy`
12 |     pub size: Vector2<T>
   |     -------------------- this field does not implement `Copy`
   |
note: the `Copy` impl for `Vector2<T>` requires that `T: Debug`
  [--> src/lib.rs:11:5
](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018#)   |
11 |     pub loc: Vector2<T>,
   |     ^^^^^^^^^^^^^^^^^^^
note: the `Copy` impl for `Vector2<T>` requires that `T: Debug`
  [--> src/lib.rs:12:5
](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018#)   |
12 |     pub size: Vector2<T>
   |     ^^^^^^^^^^^^^^^^^^^^
   = note: this error originates in the derive macro `Copy` (in Nightly builds, run with -Z macro-backtrace for more info)

It only suggests one of the missing bounds, adding T: Debug then another error suggests adding T: Copy...

[estebank]

@compiler-errors It would be nice if the obligation.cause.span that ends up being used in the "the Copy impl for Vector2<T> requires that T: Debug" note pointed at the field type, instead of the whole field as it does now. Would that be something you'd have time to explore? The actual change is simple enough, but finding where the obligation is constructed might require some exploring.

[compiler-errors]

I'll put it on my to-do list. I'm pretty sure the obligation is just constructed in can_type_implement_copy, but maybe it's a sub-obligation.

@rustbot claim