actions: notify teams upon new discussion in category

.github/workflows/discussions.yml

@@ -0,0 +1,74 @@
+---
+# This workflow notifies working groups about new discussions in their corresponding
+# categories, by mentioning the Team in a first comment.
+# It is necessary since GitHub doesn't support subsriptions to discussion categories
+# see related feature request: https://github.com/orgs/community/discussions/3951
+# If GitHub implements this feature, this workflow becomes obsolete.
+
+name: Notify Team on New Discussion
+"on":
+  discussion:
+    types: [created]
+
+jobs:
+  notify_team:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Notify Team
+        uses: actions/github-script@v7
+        with:
+          github-token: ${{ secrets.DISCUSSIONS_NOTIFICATIONS }}
+          script: |
+            const discussion = context.payload.discussion;
+            const category = discussion.category.name;
+
+            const query = `
+              query($discussionNumber: Int!) {
+                repository(
+                  owner: "${context.repo.owner}",
+                  name: "${context.repo.repo}"
+                ) {
+                  discussion(number: $discussionNumber) {
+                    id
+                  }
+                }
+              }
+            `;
+
+            const mutation = `
+              mutation($discussionId: ID!, $body: String!) {
+                addDiscussionComment(
+                  input: {discussionId: $discussionId, body: $body}
+                ) {
+                  comment {
+                    id
+                    body
+                  }
+                }
+              }
+            `;
+
+            const response = await github.graphql(query, {
+              discussionNumber: discussion.number
+            });
+
+            const discussionId = response.repository.discussion.id;
+
+            const teams = await github.rest.teams.list({
+              org: context.repo.owner,
+            });
+
+            const team = teams.data.find(t => t.name === category);
+
+            if (team) {
+              const teamMention = `${context.repo.owner}/${team.slug}`;
+              const commentBody = `@${teamMention} A new discussion was created in the`
+                                   + ` "${category}" category: ${discussion.html_url}`;
+
+              await github.graphql(mutation, {
+                discussionId: discussionId,
+                body: commentBody
+              });
+            } else {
+              console.log(`No team found for category: ${category}`);
+            }