Add Diff Javadoc workflow

.github/workflows/diff-javadoc.yml

@@ -0,0 +1,58 @@
+name: Diff Javadoc
+
+on:
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-22.04
+    permissions:
+      pull-requests: write
+    steps:
+      - name: Make Dir
+        run: mkdir ~/diff
+
+      - uses: actions/checkout@v3
+        with:
+          ref: ${{ github.base_ref }}
+
+      - name: Set up JDK 11
+        uses: actions/setup-java@v2
+        with:
+          java-version: 11
+          distribution: temurin
+          cache: gradle
+
+      - name: Build
+        run: ./gradlew kotlindoc
+
+      - name: Move original docs
+        run: mv build ~/diff/original
+
+      - uses: actions/checkout@v3
+
+      - name: Build
+        run: ./gradlew kotlindoc
+
+      - name: Move modified docs
+        run: mv build ~/diff/modified
+
+      - name: Diff docs
+        run: >
+          `# Recursively diff directories, including new files, git style, with 3 lines of context`
+          diff -wEburN ~/diff/original ~/diff/modified
+          `# Remove the first line and new file signifier of the output`
+          | tail -n +2
+          `# Replace the diff new file signifier with the end and start of a new codeblock`
+          | sed "s/^diff.*$/\`\`\`\\n\`\`\`diff/g"
+          `# Add a collapsable block, summary, and start the first code block on the first line`
+          | sed "1s/^/<details>\\n<summary>Javadoc Changes:<\/summary>\\n\\n\`\`\`diff\\n/"
+          `# Close the final code block and close the collapsable on the final line`
+          | sed "$ s/$/\\n\`\`\`\\n<\/details>/"
+          `# Write to diff.md for later`
+          > diff.md
+
+      - name: Add comment
+        uses: mshick/add-pr-comment@v2
+        with:
+          message-path: diff.md