Show a warning at the end of the diagnostic list if there are any fatal warnings (#17855)

crates/ruff_db/src/diagnostic/mod.rs

@@ -674,6 +674,10 @@ impl Severity {
             Severity::Fatal => AnnotateLevel::Error,
         }
     }
+
+    pub const fn is_fatal(self) -> bool {
+        matches!(self, Severity::Fatal)
+    }
 }
 
 /// Configuration for rendering diagnostics.

crates/ty/src/main.rs

@@ -306,6 +306,10 @@ impl MainLoop {
                                 if diagnostics_count > 1 { "s" } else { "" }
                             )?;
 
+                            if max_severity.is_fatal() {
+                                tracing::warn!("A fatal occurred while checking some files. Not all project files were analyzed. See the diagnostics list above for details.");
+                            }
+
                             if self.watcher.is_none() {
                                 return Ok(match max_severity {
                                     Severity::Info => ExitStatus::Success,