[red-knot] Use line/column for server diagnostics if available (#12881)

## Summary

This PR adds very basic support for using the line / column information
from the diagnostic message. This makes it easier to validate
diagnostics in an editor as oppose to going through the diff one
diagnostic at a time and confirming it at the location.

crates/red_knot_server/src/server/api/requests/diagnostic.rs

@@ -2,8 +2,9 @@ use std::borrow::Cow;
 
 use lsp_types::request::DocumentDiagnosticRequest;
 use lsp_types::{
-    Diagnostic, DocumentDiagnosticParams, DocumentDiagnosticReport, DocumentDiagnosticReportResult,
+    Diagnostic, DiagnosticSeverity, DocumentDiagnosticParams, DocumentDiagnosticReport,
-    FullDocumentDiagnosticReport, Range, RelatedFullDocumentDiagnosticReport, Url,
+    DocumentDiagnosticReportResult, FullDocumentDiagnosticReport, Position, Range,
+    RelatedFullDocumentDiagnosticReport, Url,
 };
 
 use red_knot_workspace::db::RootDatabase;
@@ -56,9 +57,31 @@ fn compute_diagnostics(snapshot: &DocumentSnapshot, db: &RootDatabase) -> Vec<Di
     diagnostics
         .as_slice()
         .iter()
-        .map(|message| Diagnostic {
+        .map(|message| to_lsp_diagnostic(message))
-            range: Range::default(),
+        .collect()
-            severity: None,
+}
+
+fn to_lsp_diagnostic(message: &str) -> Diagnostic {
+    let words = message.split(':').collect::<Vec<_>>();
+
+    let (range, message) = match words.as_slice() {
+        [_filename, line, column, message] => {
+            let line = line.parse::<u32>().unwrap_or_default();
+            let column = column.parse::<u32>().unwrap_or_default();
+            (
+                Range::new(
+                    Position::new(line.saturating_sub(1), column.saturating_sub(1)),
+                    Position::new(line, column),
+                ),
+                message.trim(),
+            )
+        }
+        _ => (Range::default(), message),
+    };
+
+    Diagnostic {
+        range,
+        severity: Some(DiagnosticSeverity::ERROR),
         tags: None,
         code: None,
         code_description: None,
@@ -66,6 +89,5 @@ fn compute_diagnostics(snapshot: &DocumentSnapshot, db: &RootDatabase) -> Vec<Di
         message: message.to_string(),
         related_information: None,
         data: None,
-        })
+    }
-        .collect()
 }