Add simple EPUB fatals check

Author: m-aciek

.github/workflows/reusable-docs.yml

@@ -75,13 +75,6 @@ jobs:
           --fail-if-regression \
           --fail-if-improved \
           --fail-if-new-news-nit
-    - name: 'Build and check EPUB documentation'
-      continue-on-error: true
-      run: |
-        set -Eeuo pipefail
-        make -C Doc/ PYTHON=../python SPHINXOPTS="--quiet --fail-on-warning" epub
-        pip install epubcheck
-        epubcheck Doc/build/epub/Python.epub
 
   # Run "doctest" on HEAD as new syntax doesn't exist in the latest stable release
   doctest:
@@ -109,3 +102,31 @@ jobs:
     # Use "xvfb-run" since some doctest tests open GUI windows
     - name: 'Run documentation doctest'
       run: xvfb-run make -C Doc/ PYTHON=../python SPHINXERRORHANDLING="--fail-on-warning" doctest
+
+  epubcheck:
+    name: 'Docs EPUB check'
+    runs-on: ubuntu-latest
+    timeout-minutes: 40
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        persist-credentials: false
+    - uses: actions/cache@v4
+      with:
+        path: ~/.cache/pip
+        key: ubuntu-doc-${{ hashFiles('Doc/requirements.txt') }}
+        restore-keys: |
+          ubuntu-doc-
+    - name: 'Install build dependencies'
+      run: make -C Doc/ PYTHON=../python venv
+    - name: 'Build and load EPUB checks to file'
+      continue-on-error: true
+      run: |
+        set -Eeuo pipefail
+        make -C Doc/ PYTHON=../python SPHINXOPTS="--quiet --fail-on-warning" epub
+        pip install epubcheck
+        epubcheck Doc/build/epub/Python.epub &> Doc/epubcheck.txt
+    - name: 'Check for FATAL errors in EPUB'
+      if: github.event_name == 'pull_request'
+      run: |
+        python Doc/tools/check-epub.py

Doc/tools/check-epub.py

@@ -0,0 +1,26 @@
+import sys
+from pathlib import Path
+
+
+def main():
+    wrong_directory_msg = "Must run this script from the repo root"
+    if not Path("Doc").exists() or not Path("Doc").is_dir():
+        raise RuntimeError(wrong_directory_msg)
+
+    with Path("Doc/epubcheck.txt").open(encoding="UTF-8") as f:
+        warnings = f.read().splitlines()
+
+    warnings = [warning.split(" - ") for warning in warnings]
+
+    fatals = [warning for warning in warnings if warning[0] == "FATAL"]
+
+    if fatals:
+        print("\nError: must not contain fatal errors:\n")
+        for fatal in fatals:
+            print(" - ".join(fatal))
+
+    return len(fatals)
+
+
+if __name__ == "__main__":
+    sys.exit(main())