From 4362b52a0124cbb91bec047b919fda13c4dbb1e0 Mon Sep 17 00:00:00 2001
From: Chris Russell <8494645+chescock@users.noreply.github.com>
Date: Wed, 20 Nov 2024 22:52:10 -0500
Subject: [PATCH] Add a note to the on_unimplemented message for `QueryData`
 recommending `&T` and `&mut T`. (#16449)

# Objective

A new user is likely to try `Query<Component>` instead of
`Query<&Component>`. The error message should guide them to the right
solution.

## Solution

Add a note to the on_unimplemented message for `QueryData` recommending
`&T` and `&mut T`.

The full error message now looks like:

```
error[E0277]: `A` is not valid to request as data in a `Query`
   --> crates\bevy_ecs\src\query\world_query.rs:260:18
    |
260 | fn system(query: Query<A>) {}
    |                  ^^^^^^^^ invalid `Query` data
    |
    = help: the trait `fetch::QueryData` is not implemented for `A`
    = note: if `A` is a component type, try using `&A` or `&mut A`
    = help: the following other types implement trait `fetch::QueryData`:
              &'__w mut T
              &Archetype
              &T
              ()
              (F,)
              (F0, F1)
              (F0, F1, F2)
              (F0, F1, F2, F3)
            and 41 others
note: required by a bound in `system::query::Query`
   --> crates\bevy_ecs\src\system\query.rs:362:37
    |
362 | pub struct Query<'world, 'state, D: QueryData, F: QueryFilter = ()> {
    |                                     ^^^^^^^^^ required by this bound in `Query`
```
---
 crates/bevy_ecs/src/query/fetch.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/crates/bevy_ecs/src/query/fetch.rs b/crates/bevy_ecs/src/query/fetch.rs
index de3796190f..77f40555c2 100644
--- a/crates/bevy_ecs/src/query/fetch.rs
+++ b/crates/bevy_ecs/src/query/fetch.rs
@@ -272,7 +272,8 @@ use smallvec::SmallVec;
 /// [`ReadOnly`]: Self::ReadOnly
 #[diagnostic::on_unimplemented(
     message = "`{Self}` is not valid to request as data in a `Query`",
-    label = "invalid `Query` data"
+    label = "invalid `Query` data",
+    note = "if `{Self}` is a component type, try using `&{Self}` or `&mut {Self}`"
 )]
 pub unsafe trait QueryData: WorldQuery {
     /// The read-only variant of this [`QueryData`], which satisfies the [`ReadOnlyQueryData`] trait.