[WIP]: new-plugin CI workflow

.github/workflows/new-plugin.yml

@@ -0,0 +1,149 @@
+name: new-plugin
+on:
+  push:
+    branch:
+      - "main"
+    paths:
+      - "plugins/**"
+
+# Prevent running this workflow concurrently
+concurrency:
+  group: "matrix-messages"
+
+jobs:
+  setup:
+    name: Collect metadata and setup job matrix
+    runs-on: ubuntu-latest
+    timeout-minutes: 40
+    if: github.repository == 'nix-community/nixvim'
+
+    outputs:
+      plugins: ${{ steps.get_info.outputs.json }}
+      pr_number: ${{ steps.pr.outputs.number }}
+      pr_url: ${{ steps.get_pr.outputs.url }}
+      pr_author_name: ${{ steps.get_pr.outputs.author_name }}
+      pr_author_url: ${{ steps.get_pr.outputs.author_url }}
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Install Nix
+        uses: cachix/install-nix-action@v26
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+          github_access_token: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Get plugins info
+        id: get_info
+        run: |
+          # Use `nix eval` to get json arrays containing plugins available on the pushed commit, and the previous commit
+          OLD_PLUGINS=$(
+            nix eval 'github:${{ github.repository }}/${{ github.event.before }}#nixvimConfiguration.options.plugins' \
+              --apply 'builtins.attrNames' \
+              --json
+          )
+          NEW_PLUGINS=$(
+            nix eval '.#nixvimConfiguration.options.plugins' \
+              --apply 'builtins.attrNames' \
+              --json
+          )
+          OLD_COLORSCHEMES=$(
+            nix eval 'github:${{ github.repository }}/${{ github.event.before }}#nixvimConfiguration.options.colorschemes' \
+              --apply 'builtins.attrNames' \
+              --json
+          )
+          NEW_COLORSCHEMES=$(
+            nix eval '.#nixvimConfiguration.options.colorschemes' \
+              --apply 'builtins.attrNames' \
+              --json
+          )
+          PLUGIN_JSON="{ \"old\": $OLD_PLUGINS, \"new\": $NEW_PLUGINS }"
+          COLORSCHEME_JSON="{ \"old\": $OLD_COLORSCHEMES, \"new\": $NEW_COLORSCHEMES }"
+
+          # Collect added/removed plugins by subtracting old/new arrays
+          GROUPED="{
+            \"added\": {
+              \"plugin\": $(echo "$PLUGIN_JSON" | jq '.new-.old'),
+              \"colorscheme\": $(echo "$COLORSCHEME_JSON" | jq '.new-.old')
+            },
+            \"removed\": {
+              \"plugin\": $(echo "$PLUGIN_JSON" | jq '.old-.new'),
+              \"colorscheme\": $(echo "$COLORSCHEME_JSON" | jq '.old-.new')
+            }
+          }"
+
+          # Un-group types to `{ "added": [ { "type": "plugin", "name": "foo" } ], "removed": [] }`
+          GROUPED_BY_CHANGE=$(echo "$GROUPED" | jq -c 'map_values(to_entries | map(.key as $type | .value[] | { type: $type, name: . }))')
+          # TODO: When plugins are removed, try to detect renames heuristically
+
+          # Write to GITHUB_OUTPUT
+          JSON=$(echo "$GROUPED_BY_CHANGE" | jq -c 'to_entries | map(.key as $change | .value[] | . += { change: $change })')
+          echo "json=$JSON" >> $GITHUB_OUTPUT
+
+      - name: Get PR info
+        id: get_pr
+        if: steps.get_info.outputs.json != '[]'
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          # `gh` will have already printed to stderr, so no need to parse the response json
+          JSON=$(
+            gh api  \
+              -H "Accept: application/vnd.github+json" \
+              -H "X-GitHub-Api-Version: 2022-11-28" \
+              /repos/${{ github.repository }}/commits/${{ github.sha }}/pulls
+          ) || exit 1
+
+          if [[ "$(echo "$JSON" | jq -c '.')" = "[]" ]]; then
+            # No associated PR
+            # TODO: does this need special handling?
+          else
+            # Print key=value pairs to GITHUB_OUTPUT
+            echo "$JSON" | \
+              jq -r '.[0] | { number: .number, url: .html_url, author_name: .user.login, author_url: .user.html_url } | to_entries[] | "\(.key)=\(.value)"' \
+              >> $GITHUB_OUTPUT
+          fi
+
+  send:
+    name: Send matrix message
+    runs-on: ubuntu-latest
+    needs: setup
+    strategy:
+      matrix:
+        plugins: ${{ fromJSON(needs.setup.outputs.plugins) }}
+    env:
+      name: ${{ matrix.plugins.name }}
+      type: ${{ matrix.plugins.type }}
+      change: ${{ matrix.plugins.change }}
+      pr_number: ${{ needs.setup.outputs.pr_number }}
+      pr_url: ${{ needs.setupt_pr.outputs.pr_url }}
+      pr_author_name: ${{ needs.setupt_pr.outputs.pr_author_name }}
+      pr_author_url: ${{ needs.setupt_pr.outputs.pr_author_url }}
+
+    steps:
+      - name: Install matrix-msg tool
+        uses: lkiesow/matrix-notification@v1
+        with:
+          token: ${{ secrets.CI_MATRIX_TOKEN }}
+          server: ${{ secrets.CI_MATRIX_SERVER }}
+          room: ${{ secrets.CI_MATRIX_ROOM }}
+          tool: true
+
+      - name: Send message and print summary
+        run: |
+          # Message text; plain-text & html
+          # TODO: format as-per existing announcements
+          # See available env-vars above
+          msg="Hello, world!"
+          html_msg="Hello, <b>world!</b>"
+
+          # stdout
+          echo "$msg"
+
+          # markdown summary
+          echo "$html_msg" >> $GITHUG_STEP_SUMMARY
+
+          # matrix message
+          matrix-msg "$msg" "$html_msg"
+          # TODO: update stdout/step_summary with msg success/failure