rust: pin-init: internal: add custom diagnostic when `#[pin_data]` is not implemented

Produce a more helpful error message when `#[pin_data]` is omitted. The
error message changes from

    error[E0277]: the trait bound `Foo: pin_init::__internal::HasPinData` is not satisfied
     --> tests/ui/compile-fail/init/missing_pin_data.rs:9:19
      |
    9 |         pin_init!(Self { a: 42 })
      |                   ^^^^ unsatisfied trait bound
      |
    help: the trait `pin_init::__internal::HasPinData` is not implemented for `Foo`
     --> tests/ui/compile-fail/init/missing_pin_data.rs:3:1
      |
    3 | struct Foo {
      | ^^^^^^^^^^

to

    error[E0277]: `Foo` cannot be used with `pin_init!` macro
     --> tests/ui/compile-fail/init/missing_pin_data.rs:9:19
      |
    9 |         pin_init!(Self { a: 42 })
      |                   ^^^^ unsatisfied trait bound
      |
    help: the trait `pin_init::__internal::HasPinData` is not implemented for `Foo`
     --> tests/ui/compile-fail/init/missing_pin_data.rs:3:1
      |
    3 | struct Foo {
      | ^^^^^^^^^^
      = note: did you forget to add `#[pin_data]` attribute to the struct?

Link: https://patch.msgid.link/20260923-dev-pin-data-diag-v1-4-e4d7193569e5@garyguo.net
Signed-off-by: Gary Guo <gary@garyguo.net>

0 files changed, 0 insertions, 0 deletions