Rollup merge of rust-lang#149020 - RalfJung:flush_delayed, r=nnethercote

flush_delayed: add note about stashed diagnostics

r? `@nnethercote`
Is `emit_stashed_diagnostics` the right advice to give? The other option seems to be to call `finish_diagnostics`. That's what I ended up doing (for now) in rust-lang/miri#4702 because it best matches what happens during normal compilation.

Author: GuillaumeGomez

compiler/rustc_errors/src/lib.rs

@@ -1205,6 +1205,10 @@ impl<'a> DiagCtxtHandle<'a> {
         std::mem::take(&mut self.inner.borrow_mut().fulfilled_expectations)
     }
 
+    /// Trigger an ICE if there are any delayed bugs and no hard errors.
+    ///
+    /// This will panic if there are any stashed diagnostics. You can call
+    /// `emit_stashed_diagnostics` to emit those before calling `flush_delayed`.
     pub fn flush_delayed(&self) {
         self.inner.borrow_mut().flush_delayed();
     }