misleading E0392 "parameter `T` is never used" for every containing struct

[geogriff-signal]

Rustc emits an error for every struct containing a struct with an unused type parameter. Unless there's some edge case I'm not thinking of, this seems pointless, as the user will eventually have to fix the "leaf" struct (that which is the root of the problem), which would then fix the entire tree of structs.

I tried this code:

struct Foo<T> {
    bar: Bar<T>,
}
struct Bar<T> {}

I expected to see this happen:

error[E0392]: parameter `T` is never used
 --> src/main.rs:4:12
  |
5 | struct Bar<T> {}
  |            ^ unused parameter
  |
  = help: consider removing `T`, referring to it in a field, or using a marker such as `std::marker::PhantomData`

error: aborting due to previous error

Instead, this happened:

error[E0392]: parameter `T` is never used
 --> src/main.rs:1:12
  |
1 | struct Foo<T> {
  |            ^ unused parameter
  |
  = help: consider removing `T`, referring to it in a field, or using a marker such as `std::marker::PhantomData`

error[E0392]: parameter `T` is never used
 --> src/main.rs:4:12
  |
4 | struct Bar<T> {}
  |            ^ unused parameter
  |
  = help: consider removing `T`, referring to it in a field, or using a marker such as `std::marker::PhantomData`

error: aborting due to 2 previous errors

Meta

rustc --version --verbose:
rustc 1.41.0-nightly (25d8a94 2019-11-29)
binary: rustc
commit-hash: 25d8a94
commit-date: 2019-11-29
host: x86_64-unknown-linux-gnu
release: 1.41.0-nightly
LLVM version: 9.0

[steveklabnik]

Triage: trying this today, the same error happens.