GitHub Actions: create a tag to our repo weekly if a new change is co…

…mmitted since last tagging

Partially close #1038.

The tagging format is p5.9.YYYYMMDD.0.

@k-takata helped me utilize git describe/tag.

.github/workflows/tagging.yml

@@ -0,0 +1,26 @@
+name: Create a periodical tag
+
+on:
+  schedule:
+    - cron:  '0 0 * * 0'
+
+env:
+  # Account for creating a tag
+  USER_NAME: "Universal-ctags CI"
+  USER_EMAIL: "Universal-ctags@users.noreply.github.com"
+
+jobs:
+  tag:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        path: ctags
+
+    - name: create a weekly tag
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      run: |
+        cd ctags
+        misc/git-tag-maybe.sh

misc/git-tag-maybe.sh

@@ -0,0 +1,36 @@
+#!/bin/sh
+
+base=5.9
+cal=$(date +%Y%m%d)
+chicken=0
+tag="p${base}.${cal}.${chicken}"
+
+if desc=$(git describe --tags --exact-match); then
+	case "${desc}" in
+		p*.0)
+			echo "do nothing because nothing happens since last tagging"
+			exit 0
+			;;
+		*)
+			echo "found a tag but it is not periodical one; create a periodical tag"
+			;;
+	esac
+fi
+
+r=0
+desc=$(git describe --tags --always)
+printf "%s (%s <= %s)..." "create tag" "${desc}" "${tag}"
+if git tag "${tag}"; then
+	echo "done"
+	printf "push the tag..."
+	if git push origin --tags; then
+		echo "done"
+	else
+		echo "failed"
+		r=2
+	fi
+else
+	echo "failed"
+	r=1
+fi
+exit $r