Check newsfile more carefully (correct number, correct punctuation)

.github/workflows/changelog_check.yml

@@ -3,6 +3,7 @@ on: [pull_request]
 
 jobs:
   check-newsfile:
+    if: ${{ github.base_ref == 'main'  || contains(github.base_ref, 'release-') }}
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
@@ -13,4 +14,4 @@ jobs:
         with:
           python-version: "3.7"
       - run: python -m pip install towncrier
-      - run: python -m towncrier.check --compare-with="origin/main"
+      - run: "scripts-dev/check_newsfragment.sh ${{ github.event.number }}"

changelog.d/250.misc

@@ -0,0 +1 @@
+Add more comprehensive Newsfile (changelog fragment) checks in CI.

scripts-dev/check_newsfragment.sh

@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+#
+# A script which checks that an appropriate news file has been added on this
+# branch.
+
+echo -e "+++ \033[32mChecking newsfragment\033[m"
+
+set -e
+
+pr="$1"
+
+# Print a link to the contributing guide if the user makes a mistake
+CONTRIBUTING_GUIDE_TEXT="!! Please see the contributing guide for help writing your changelog entry:
+https://github.com/matrix-org/sygnal/blob/main/CONTRIBUTING.md#changelog"
+
+# If towncrier returns a non-zero exit code, print the contributing guide link and exit
+python -m towncrier.check --compare-with="origin/main" || (echo -e "$CONTRIBUTING_GUIDE_TEXT" >&2 && exit 1)
+
+echo
+echo "--------------------------"
+echo
+
+matched=0
+for f in `git diff --name-only FETCH_HEAD... -- changelog.d`; do
+    # check that any modified newsfiles on this branch end with a full stop.
+    lastchar=`tr -d '\n' < $f | tail -c 1`
+    if [ $lastchar != '.' -a $lastchar != '!' ]; then
+        echo -e "\e[31mERROR: newsfragment $f does not end with a '.' or '!'\e[39m" >&2
+        echo -e "$CONTRIBUTING_GUIDE_TEXT" >&2
+        exit 1
+    fi
+
+    # see if this newsfile corresponds to the right PR
+    [[ -n "$pr" && "$f" == changelog.d/"$pr".* ]] && matched=1
+done
+
+if [[ -n "$pr" && "$matched" -eq 0 ]]; then
+    echo -e "\e[31mERROR: Did not find a news fragment with the right number: expected changelog.d/$pr.*.\e[39m" >&2
+    echo -e "$CONTRIBUTING_GUIDE_TEXT" >&2
+    exit 1
+fi

setup.py

@@ -47,6 +47,7 @@
         "mypy==0.812",
         "mypy-zope==0.3.0",
         "tox",
+        "towncrier",
     ]
 }