Publish documentation snapshot only if necessary

.travis.yml

@@ -72,4 +72,4 @@ jobs:
       env:
         # GRGIT_USER
         - secure: PwwKcsVdukfzvDBHmdajhMsIVHSbPt+lorgibpRXImBt+C4XHlaz/Z78Bq8jtkDvrXb+DTSfSGvAxg1IBM+rtCzrYb5DAqq+OfuG9Uu6FDTnkIOHs5Gii7pAfT0+W31Oj76OgiCAXX+p8lbFTchz6ope5zVYEpSlAe7aXCVTGM0=
-      script: ./gradlew --scan gitPublishPush
+      script: ./src/publishDocumentationSnapshotOnlyIfNecessary.sh

gradle/gh-pages.gradle

@@ -7,6 +7,9 @@ task prepareDocsForUploadToGhPages(type: Copy) {
 	dependsOn 'aggregateJavadocs', ':documentation:asciidoctor'
 	outputs.dir docsDir
 
+	from("${project(':documentation').buildDir}") {
+		include 'published-checksum.txt'
+	}
 	from("${project(':documentation').buildDir}/asciidoc") {
 		include 'user-guide/**'
 		include 'release-notes/**'

src/publishDocumentationSnapshotOnlyIfNecessary.sh

@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+
+readonly current='documentation/build/current-checksum.txt'
+readonly published='documentation/build/published-checksum.txt'
+readonly github_pages_url='https://raw.githubusercontent.com/junit-team/junit5/gh-pages/docs/snapshot/published-checksum.txt'
+
+#
+# always generate current sums
+#
+echo "Generating checksum file..."
+md5sum documentation/documentation.gradle > "${current}"
+md5sum $(find documentation/src/ -type f) >> "${current}"
+md5sum $(find . -wholename '**/src/main/java/*.java') >> "${current}"
+stat "${current}"
+md5sum "${current}"
+
+#
+# compare current with published sums
+#
+curl --silent --output "${published}" "${github_pages_url}"
+if cmp --silent "${current}" "${published}" ; then
+  #
+  # no changes detected: we're done
+  #
+  echo "Already published documentation with same source checksum."
+else
+  #
+  # update checksum file and trigger new documentation build and upload
+  #
+  echo "Creating and publishing documentation..."
+  cp --force "${current}" "${published}"
+  ./gradlew --scan gitPublishPush
+fi