UI: Fix log line number gaps caused by group markers

airflow-core/src/airflow/ui/src/components/renderStructuredLog.tsx

@@ -274,7 +274,7 @@ const renderStructuredLogImpl = ({
   }
 
   return (
-    <chakra.div display="flex" key={index} lineHeight={1.5}>
+    <chakra.div alignItems="flex-start" display="flex" key={index} lineHeight={1.5}>
       <RouterLink
         id={index.toString()}
         key={`line_${index}`}

airflow-core/src/airflow/ui/src/pages/TaskInstance/Logs/Logs.test.tsx

@@ -133,4 +133,38 @@ describe("Task log grouping", () => {
 
     await waitFor(() => expect(screen.queryByText(/Marking task as SUCCESS/iu)).not.toBeVisible());
   }, 10_000);
+
+  it("Has sequential line numbers with no gaps or duplicates", async () => {
+    render(
+      <AppWrapper initialEntries={["/dags/log_grouping/runs/manual__2025-02-18T12:19/tasks/generate"]} />,
+    );
+
+    await waitForLogs();
+
+    // Expand all groups so their content lines are in the DOM
+    const summaryPre = screen.getByTestId("summary-Pre task execution logs");
+
+    fireEvent.click(summaryPre);
+    await waitFor(() => expect(screen.getByText(/starting attempt 1 of 3/iu)).toBeVisible());
+
+    const summaryPost = screen.getByTestId("summary-Post task execution logs");
+
+    fireEvent.click(summaryPost);
+    await waitFor(() => expect(screen.queryByText(/Marking task as SUCCESS/iu)).toBeVisible());
+
+    // Collect all rendered line number links
+    const lineNumbers = [...document.querySelectorAll<HTMLAnchorElement>("a[id]")]
+      .map((el) => parseInt(el.id, 10))
+      .filter((num) => !isNaN(num))
+      .sort((numA, numB) => numA - numB);
+
+    expect(lineNumbers.length).toBeGreaterThan(0);
+    expect(lineNumbers[0]).toBe(0);
+    expect(new Set(lineNumbers).size).toBe(lineNumbers.length);
+
+    // No gaps
+    lineNumbers.forEach((num, idx) => {
+      expect(num).toBe(idx);
+    });
+  }, 10_000);
 });

airflow-core/src/airflow/ui/src/queries/useLogs.tsx

@@ -75,6 +75,20 @@ const parseLogs = ({
   const logLink = taskInstance ? `${getTaskInstanceLink(taskInstance)}?try_number=${tryNumber}` : "";
 
   try {
+    let lineNumber = 0;
+    const lineNumbers = data.map((datum, dataIndex) => {
+      const text = typeof datum === "string" ? datum : datum.event;
+
+      if (text.includes("::group::") || text.includes("::endgroup::")) {
+        return dataIndex;
+      }
+      const current = lineNumber;
+
+      lineNumber += 1;
+
+      return current;
+    });
+
     parsedLines = data
       .map((datum, index) => {
         if (typeof datum !== "string" && "logger" in datum) {
@@ -86,7 +100,7 @@ const parseLogs = ({
         }
 
         return renderStructuredLog({
-          index,
+          index: lineNumbers[index] ?? index,
           logLevelFilters,
           logLink,
           logMessage: datum,