Extend empty diagnostic ranges at the ends of lines

crates/language/src/lib.rs

@@ -751,6 +751,10 @@ impl Buffer {
                     if range.start == range.end {
                         range.end.column += 1;
                         range.end = content.clip_point_utf16(range.end, Bias::Right);
+                        if range.start == range.end && range.end.column > 0 {
+                            range.start.column -= 1;
+                            range.start = content.clip_point_utf16(range.start, Bias::Left);
+                        }
                     }
                     Some((
                         range,

crates/language/src/tests.rs

@@ -633,6 +633,66 @@ async fn test_diagnostics(mut cx: gpui::TestAppContext) {
             ]
         );
     });
+}
+
+#[gpui::test]
+async fn test_empty_diagnostic_ranges(mut cx: gpui::TestAppContext) {
+    cx.add_model(|cx| {
+        let text = concat!(
+            "let one = ;\n", //
+            "let two = \n",
+            "let three = 3;\n",
+        );
+
+        let mut buffer = Buffer::new(0, text, cx);
+        buffer.set_language(Some(Arc::new(rust_lang())), None, cx);
+        buffer
+            .update_diagnostics(
+                None,
+                vec![
+                    lsp::Diagnostic {
+                        range: lsp::Range::new(
+                            lsp::Position::new(0, 10),
+                            lsp::Position::new(0, 10),
+                        ),
+                        severity: Some(lsp::DiagnosticSeverity::ERROR),
+                        message: "syntax error 1".to_string(),
+                        ..Default::default()
+                    },
+                    lsp::Diagnostic {
+                        range: lsp::Range::new(
+                            lsp::Position::new(1, 10),
+                            lsp::Position::new(1, 10),
+                        ),
+                        severity: Some(lsp::DiagnosticSeverity::ERROR),
+                        message: "syntax error 2".to_string(),
+                        ..Default::default()
+                    },
+                ],
+                cx,
+            )
+            .unwrap();
+
+        // An empty range is extended forward to include the following character.
+        // At the end of a line, an empty range is extended backward to include
+        // the preceding character.
+        let chunks = chunks_with_diagnostics(&buffer, 0..buffer.len());
+        assert_eq!(
+            chunks
+                .iter()
+                .map(|(s, d)| (s.as_str(), *d))
+                .collect::<Vec<_>>(),
+            &[
+                ("let one = ", None),
+                (";", Some(lsp::DiagnosticSeverity::ERROR)),
+                ("\nlet two =", None),
+                (" ", Some(lsp::DiagnosticSeverity::ERROR)),
+                ("\nlet three = 3;\n", None)
+            ]
+        );
+        buffer
+    });
+}
 
 fn chunks_with_diagnostics<T: ToOffset>(
     buffer: &Buffer,
@@ -651,7 +711,6 @@ async fn test_diagnostics(mut cx: gpui::TestAppContext) {
     }
     chunks
 }
-}
 
 #[test]
 fn test_contiguous_ranges() {