Add backwards compatibility to nested job log sections

This adds backwards compatibility to the nested
collapsible sections, this is behind the
`infinitely_collapsible_sections` feature flag

app/assets/javascripts/jobs/store/utils.js

@@ -174,7 +174,7 @@ export const logLinesParser = (lines = [], previousTraceState = {}, prevParsedLi
         parsedLines[currentHeader.index].line.section_duration = line.section_duration;
         isPreviousLineHeader = false;
         currentHeader = null;
-      } else {
+      } else if (currentHeader?.isHeader) {
         currentHeader.line.section_duration = line.section_duration;
 
         if (previousSection && previousSection?.index) {
@@ -185,6 +185,11 @@ export const logLinesParser = (lines = [], previousTraceState = {}, prevParsedLi
         }
 
         currentHeader = previousSection;
+      } else {
+        // On older job logs, there's no `section_header: true` response, it's just an object
+        // with the `section_duration` and `section` props, so we just parse it
+        // as a standard line
+        parsedLines.push(parseLine(line, currentLineCount));
       }
     } else {
       parsedLines.push(parseLine(line, currentLineCount));

spec/frontend/jobs/components/log/mock_data.js

@@ -123,6 +123,15 @@ export const multipleCollapsibleSectionsMockData = [
   },
 ];
 
+export const backwardsCompatibilityTrace = [
+  {
+    offset: 2365,
+    content: [],
+    section: 'download-artifacts',
+    section_duration: '00:01',
+  },
+];
+
 export const originalTrace = [
   {
     offset: 1,

spec/frontend/jobs/store/utils_spec.js

@@ -19,6 +19,7 @@ import {
   collapsibleTrace,
   collapsibleTraceIncremental,
   multipleCollapsibleSectionsMockData,
+  backwardsCompatibilityTrace,
 } from '../components/log/mock_data';
 
 describe('Jobs Store Utils', () => {
@@ -297,6 +298,21 @@ describe('Jobs Store Utils', () => {
         expect(result.parsedLines[1].lines).toEqual(expect.arrayContaining(innerSection));
       });
     });
+
+    describe('backwards compatibility', () => {
+      beforeEach(() => {
+        result = logLinesParser(backwardsCompatibilityTrace);
+      });
+
+      it('should return an object with a parsedLines prop', () => {
+        expect(result).toEqual(
+          expect.objectContaining({
+            parsedLines: expect.any(Array),
+          }),
+        );
+        expect(result.parsedLines).toHaveLength(1);
+      });
+    });
   });
 
   describe('findOffsetAndRemove', () => {