Subsection navigation is inconsistent and not updated after reordering

[cmoehl]

Description
Navigation between subsections is not updated correctly. The previous/next navigation treats sections and subsections inconsistently and does not reflect the actual order of subsections after they have been reordered.

To Reproduce
Steps to reproduce the behaviour:

1. Create a course with 1 section.
2. Open Section 1.
3. Create Subsection 1.
4. Create Subsection 2 below Subsection 1.
5. Open Subsection 1.
   • Navigation unexpectedly shows "Section 1" on the left.
   • No navigation is shown on the right.
6. Open Subsection 2.
   • Navigation shows "Subsection 1" on the left (as expected).
   • No navigation is shown on the right (as expected).
7. Move Subsection 1 below Subsection 2.
8. Open Subsection 1.
   • Navigation still shows "Section 1" on the left.
   • No navigation is shown on the right.

Expected behaviour
Subsection navigation should reflect the current order of subsections and should treat sections and subsections as separate navigation levels.

Expected results:

• Before reordering:
  • Subsection 1: no navigation on the left; "Subsection 2" on the right.
  • Subsection 2: "Subsection 1" on the left; no navigation on the right.
• After reordering (Subsection 2 → Subsection 1):
  • Subsection 1: "Subsection 2" on the left; no navigation on the right.
  • Subsection 2: no navigation on the left; "Subsection 1" on the right.

Versions

• Moodle: 5.1.5
• Format: 500.1.0

Additional context
https://moodle.atlassian.net/browse/MDL-85755 "Section navigation does not display correct next/prev links for subsections" was fixed and is working in custom sections and weekly sections. This might help.

[cmoehl]

Dear @gjb2048

As subsection pages (MDL-87276) are removed with 5.2 this issue is gone when upgrading: Subsections won't be displayed in the previous/next navigation anymore.