Add action for moving issues to Typst Forum (#5026)

Co-authored-by: Caleb Maclennan <caleb@alerque.com>

.github/workflows/forum.yml

@@ -0,0 +1,81 @@
+name: Move to Typst Forum
+on:
+  issues:
+    types:
+      - labeled
+jobs:
+  add-comment:
+    if: github.event.label.name == 'to-forum'
+    runs-on: ubuntu-latest
+    permissions:
+      issues: write
+    steps:
+      - name: Call Discourse API to create forum post
+        env:
+          ISSUE_BODY: ${{ github.event.issue.body }}
+          ISSUE_TITLE: ${{ github.event.issue.title }}
+          ISSUE_NUMBER: ${{ github.event.issue.number }}
+          ISSUE_URL: ${{ github.event.issue.html_url }}
+          ISSUE_USER_LOGIN: ${{ github.event.issue.user.login }}
+          REPOSITORY_OWNER: ${{ github.repository_owner }}
+        run: |
+          read -d '' RAW << END_OF_BODY
+          This topic was moved from GitHub issue ${ISSUE_NUMBER}. Please continue the conversation here.
+
+          Here is the original issue:
+          [quote="${ISSUE_USER_LOGIN}"]
+          ${ISSUE_BODY}
+          [/quote]
+
+          Browse the previous discussion at ${ISSUE_URL}
+          END_OF_BODY
+
+          TITLE_JSON=$(jq -n --arg title "[#${ISSUE_NUMBER}] ${ISSUE_TITLE}" '$title')
+          RAW_JSON=$(jq -n --arg raw "$RAW" '$raw')
+          EXTERNAL_ID_JSON=$(jq -n --arg external_id "gh-${REPOSITORY_OWNER}-typst-${ISSUE_NUMBER}" '$external_id')
+
+          RESPONSE=$(curl -X POST "https://forum.typst.app/posts.json" \
+            --fail-with-body \
+            -H "Api-Key: ${{ secrets.DISCOURSE_TOKEN }}" \
+            -H "Content-Type: application/json" \
+            -d "{
+              \"title\": $TITLE_JSON,
+              \"category\": 4,
+              \"external_id\": $EXTERNAL_ID_JSON,
+              \"raw\": $RAW_JSON
+            }")
+
+          # Check if response contains errors
+          if [ $(jq -n --argjson response "$RESPONSE" '$response.errors | length') -gt 0 ]; then
+            # Join the errors with commas
+            ERRORS=$(jq -n --argjson response "$RESPONSE" '$response.errors | join(", ")')
+            echo "DISCOURSE_ERROR=$ERRORS" >> $GITHUB_ENV
+            exit 1
+          fi
+
+          # Check if the response returned a non-200 status code
+          if [ $? -ne 0 ]; then
+            echo "DISCOURSE_ERROR=Failed to call the Discourse API" >> $GITHUB_ENV
+            exit 1
+          fi
+
+          THREAD_ID="$(jq -n --argjson response "$RESPONSE" '$response.topic_id')"
+          if [ "$THREAD_ID" = 'null' ]; then
+            echo "DISCOURSE_ERROR=Failed to retrieve new thread ID" >> $GITHUB_ENV
+            exit 1
+          fi
+
+          echo "THREAD_ID=$THREAD_ID" >> $GITHUB_ENV
+      - name: Add a comment if the workflow failed
+        if: failure()
+        run: |
+          gh issue comment ${{ github.event.issue.number }} --body "Failed to move this issue to the Typst Forum. This is the error that the API call returned: $DISCOURSE_ERROR"
+      - name: Add comment and close as not planned
+        run: |
+          gh issue close "$NUMBER" --reason "not planned" --comment "$BODY"
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GH_REPO: ${{ github.repository }}
+          NUMBER: ${{ github.event.issue.number }}
+          BODY: >
+            We moved this issue to the Typst Forum. Please continue the discussion there: https://forum.typst.app/t/${{ env.THREAD_ID }}