Rollup merge of #129344 - compiler-errors:less-option-unit-diagnostics, r=jieyouxu

Use `bool` in favor of `Option<()>` for diagnostics

We originally only supported `Option<()>` for optional notes/labels, but we now support `bool`. Let's use that, since it usually leads to more readable code.

I'm not removing the support from the derive macro, though I guess we could error on it... 🤔

compiler/rustc_middle/src/error.rs

@@ -160,7 +160,7 @@ pub struct TypeLengthLimit {
     pub span: Span,
     pub shrunk: String,
     #[note(middle_written_to_path)]
-    pub was_written: Option<()>,
+    pub was_written: bool,
     pub path: PathBuf,
     pub type_length: usize,
 }

compiler/rustc_middle/src/ty/instance.rs

@@ -581,9 +581,9 @@ impl<'tcx> Instance<'tcx> {
                     let mut path = PathBuf::new();
                     let was_written = if let Some(path2) = written_to_path {
                         path = path2;
-                        Some(())
+                        true
                     } else {
-                        None
+                        false
                     };
                     tcx.dcx().emit_fatal(error::TypeLengthLimit {
                         // We don't use `def_span(def_id)` so that diagnostics point