rustdoc-json: `impl dyn Trait` gets discarded

[aDotInTheVoid]

For the following code:

pub trait T1 {
    fn number(&self) -> i32;
}

impl dyn T1 {
    pub fn number_plus_one(&self) {
        self.number() + 1
    }
}

generates

{
  "format_version": 36,
  "includes_private": false,
  "index": {
    "0": {
      "attrs": [],
      "crate_id": 0,
      "deprecation": null,
      "docs": null,
      "id": 0,
      "inner": {"function": { ... }},
      "name": "number",
      "visibility": "default"
    },
    "1": {
      "attrs": [],
      "crate_id": 0,
      "deprecation": null,
      "docs": null,
      "id": 1,
      "inner": {
        "trait": {
          "bounds": [],
          "generics": {"params": [], "where_predicates": []},
          "implementations": [],
          "is_auto": false,
          "is_dyn_compatible": true,
          "is_unsafe": false,
          "items": [0]
        }
      },
      "name": "T1",
      "visibility": "public"
    },
    "2": {
      "attrs": [],
      "crate_id": 0,
      "deprecation": null,
      "docs": null,
      "id": 2,
      "inner": {"module": {"is_crate": true, "is_stripped": false, "items": [1]}},
      "name": "on_dyn_trait",
      "visibility": "public"
    }
  },
  "root": 2
}

(full).

There's nothing included for the number_plus_one method, but there should be.

The HTML backend get this right, so the releavent info is availible in clean:

I'm not sure what's the best way to store this is in the format: Putting it into the implementations field seems wrong, as impl dyn T1 isn't an implementation of T1, but an implementation on dyn T1. I'd love to hear people's thoughts on this.

[obi1kenobi]

I'd expect a few things to happen in the rustdoc JSON here:

• an impl item corresponding to the impl dyn T1 block
• that impl item containing a number_plus_one function ("method") item
• some form of "relationship" from T1 to impl dyn T1, which isn't the implementations field but something else.

Ideally, the approach would rhyme with how we represent other edge cases like impl .. for &mut:

pub trait T1 {}

struct Example;

impl T1 for Example {}

// This impl is unrelated to the one above, and isn't technically on `Example`!
// And yet it's related to `Example` so it probably should be linked
// from the `Example` item in some manner.
impl T1 for &mut Example {}