Handle long diffs gracefully in compare-ds github action

.github/workflows/compare-ds.yaml

@@ -83,7 +83,7 @@ jobs:
           body="${body//'%'/'%25'}"
           body="${body//$'\n'/'%0A'}"
           body="${body//$'\r'/'%0D'}"
-          echo ::set-output name=log::$body
+          echo ::set-output name=log::${body:0:65000}
       - name: Find Comment
         uses: peter-evans/find-comment@v1
         id: fc
@@ -92,7 +92,7 @@ jobs:
           comment-author: 'github-actions[bot]'
           body-includes: This datastream diff is auto generated by the check
       - name: Create or update comment
-        if: ${{ steps.compare_ds.outputs.COMPARE_DS_OUTPUT_SIZE != '0'}}
+        if: ${{ steps.compare_ds.outputs.COMPARE_DS_OUTPUT_SIZE != '0' && steps.compare_ds.outputs.COMPARE_DS_OUTPUT_SIZE <= 65000 }}
         uses: peter-evans/create-or-update-comment@v1
         with:
           comment-id: ${{ steps.fc.outputs.comment-id }}
@@ -106,6 +106,26 @@ jobs:
             ${{ steps.diff.outputs.log }}
             ```
 
+            </details>
+          edit-mode: replace
+      - name: Create or update a trimmed comment
+        if: ${{ steps.compare_ds.outputs.COMPARE_DS_OUTPUT_SIZE > 65000 }}
+        uses: peter-evans/create-or-update-comment@v1
+        with:
+          comment-id: ${{ steps.fc.outputs.comment-id }}
+          issue-number: ${{ github.event.pull_request.number }}
+          body: |
+            This datastream diff is auto generated by the check `Compare DS/Generate Diff`.
+            Due to the excessive size of the diff, it has been trimmed to fit the 65535-character limit.
+            <details>
+            <summary>Click here to see the trimmed diff</summary>
+
+            ```diff
+            ${{ steps.diff.outputs.log }}
+
+            ... The diff is trimmed here ...
+            ```
+
             </details>
           edit-mode: replace
       - name: Delete existing comment in case new commits trigger no changes in Compare DS tool