Unclear "mismatched types" error

[nyurik]

As seen in this image, the inline error message is very unclear: which type do I use, vs which type I should be using instead. It simply lists two types and their source files. It requires full dialog to be open to understand which is which.

error[E0308]: mismatched types
   --> clippy_lints/src/functions/ref_option.rs:18:40
    |
18  |         if is_type_diagnostic_item(cx, *ty, sym::Option)
    |            -----------------------     ^^^ expected `rustc_middle::ty::Ty<'_>`, found `rustc_hir::Ty<'_>`
    |            |
    |            arguments to this function are incorrect
    |
    = note: `rustc_hir::Ty<'_>` and `rustc_middle::ty::Ty<'_>` have similar names, but are actually distinct types
note: `rustc_hir::Ty<'_>` is defined in crate `rustc_hir`
   --> /home/nyurik/.rustup/toolchains/nightly-2024-09-05-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/compiler/rustc_hir/src/hir.rs:2539:1
note: `rustc_middle::ty::Ty<'_>` is defined in crate `rustc_middle`
   --> /home/nyurik/.rustup/toolchains/nightly-2024-09-05-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/compiler/rustc_middle/src/ty/mod.rs:440:1
note: function defined here
   --> /home/nyurik/dev/rust/rust-clippy/clippy_utils/src/ty.rs:445:8
    |
445 | pub fn is_type_diagnostic_item(cx: &LateContext<'_>, ty: Ty<'_>, diag_item: Symbol) -> bool {
    |        ^^^^^^^^^^^^^^^^^^^^^^^

rust-analyzer version: rust-analyzer version: 0.3.2112-standalone

rustc version: rustc 1.81.0 (eeb90cda1 2024-09-04)

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[ChayimFriedman2]

The diagnostics get emitted by rustc in JSON, we have no control over them (although r-a native diagnostics are even worse currently).

[nyurik]

Makes sense, and rustc does make it clear because it uses comments on the code span itself - making it non-ambiguous. Does it make sense to show span info somewhere too in that error expansion? Or would it require rustc's message to be altered to make it clearer which type is which? Seems bad to loose span messages in r-a though...

[ChayimFriedman2]

We don't lose spans, we split the diagnostic so each part is shown on its span.