fix: add heading hierarchy check and fix set -e crash

[CybotTM]

Summary

• Bug fix: ((WARNINGS++)) with set -e crashes the script when counter is 0 (bash treats ((0)) as falsy exit code 1). All ((VAR++)) replaced with safe VAR=$((VAR + 1)) arithmetic.
• New feature: Added TYPO3 heading hierarchy validation that catches:
  • First section heading not using = (h2) — the most common mistake when extracting sections into standalone pages
  • Non-standard underline characters (e.g. ^)
  • Skipped heading levels (e.g. h2 directly to h4 without h3)

Motivation

This was discovered during TYPO3-Documentation/TYPO3CMS-Guide-HowToDocument#510 where extracted pages retained their old heading levels. The validate_docs.sh script ran but never reached the heading check due to the set -e + ((0++)) crash, and even if it had, no heading hierarchy check existed.

Test plan

• Run validate_docs.sh against a TYPO3 extension with correct headings — should pass
• Run against a file where first section uses - instead of = — should flag it
• Verify the set -e crash no longer occurs when first warning is encountered

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical bug in the validate_docs.sh script that caused it to crash under specific conditions related to set -e and arithmetic operations. Concurrently, it introduces a significant enhancement by adding comprehensive validation for TYPO3 documentation heading structures, ensuring adherence to established guidelines and improving overall document quality.

Highlights

• Bug Fix: set -e crash: Resolved a script crash when set -e was active and an arithmetic counter (e.g., ((VAR++))) was evaluated to zero, which Bash treats as a falsy exit code. All ((VAR++)) instances were replaced with VAR=$((VAR + 1)) for safe arithmetic.
• New Feature: TYPO3 Heading Hierarchy Validation: Implemented a new check to validate TYPO3 documentation heading hierarchy. This includes verifying that the first section heading uses the correct = (h2) character, detecting non-standard underline characters, and identifying skipped heading levels (e.g., jumping from h2 to h4 without an h3).

Changelog

• skills/typo3-docs/scripts/validate_docs.sh
  • Updated all instances of ((VAR++)) to VAR=$((VAR + 1)) to prevent script crashes when set -e is enabled and the counter is zero.
  • Introduced a new section for TYPO3 heading hierarchy validation, embedding a Python script to perform detailed checks on .rst files.
  • Added checks for the first section heading character, non-standard heading underline characters, and skipped heading levels.

Activity

• The pull request author, CybotTM, created this PR to fix a known issue and introduce new validation features, as detailed in the summary and motivation sections.

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[gemini-code-assist]

Code Review

This pull request fixes a crash caused by set -e and ((VAR++)) arithmetic in bash, and introduces a new feature for validating heading hierarchy in RST files. However, the implementation of this new feature introduces a critical Command Injection and Python Code Injection vulnerability. This is due to the direct interpolation of a shell variable ($file) into a Python script executed via python3 -c, which could allow an attacker to execute arbitrary code. It is recommended to refactor the embedded Python code into a separate file to resolve this security risk and improve maintainability.