Add a workflow to check practice exercises are sorted

.github/workflows/sorted.yml

@@ -0,0 +1,42 @@
+name: Check practice exercises are sorted
+
+on:
+  workflow_call:
+    inputs:
+      ordering:
+        description: "How exercises are ordered"
+        required: true
+        type: string
+
+jobs:
+  check:
+    name: Check exercises
+    runs-on: ubuntu-slim
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd
+      - name: Check if practice exercises are sorted
+        env:
+          ORDERING: ${{ inputs.ordering }}
+        run: |
+          diff <( jq -r '.exercises.practice[].slug' config.json ) <(
+            jq -r '
+              # Bucket by displayed difficulty. 0-3: easy; 4-7: medium; 8-10: hard.
+              def bucket(i): [1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3][i];
+
+              # Code injection to inject the sort literal expression.
+              def sort: sort_by('"$ORDERING"');
+
+              .exercises.practice |
+              # Add displayed difficulty
+              map(.bucket = bucket(.difficulty)) |
+              # Add lowercase name
+              map(.lowercase_name = (.name | ascii_downcase)) |
+              # Leave hello-world at the top
+              if .[0].slug == "hello-world" then
+                [.[0]] + (.[1:] | sort)
+              else
+                sort
+              end |
+              map(.slug)[]
+          ' config.json)

README.md

@@ -295,5 +295,53 @@ jobs:
     uses: exercism/github-actions/.github/workflows/labels.yml@main
 ```
 
+## Reusable workflow: sorted
+
+The `sorted` reusable workflow checks if the practice exercises on a track are sorted.
+
+### Extra fields
+
+Some extra fields are added to the exercise data for sorting.
+
+* `bucket` is added, which indicates the difficulty "bucket" or "displayed" difficulty (easy, medium, hard).
+* `lowercase_name` is added to allow sorting by exercise name, case insensitive.
+
+### Inputs
+
+The workflow takes a single input, `ordering` (required), that determines how sorting works.
+The `ordering` input is passed to `sort_by()` and must be a valid JQ path expression.
+
+Some valid ordering values:
+
+* **".name"**: sort alphabetically by the displayed name
+* **".lowercase_name"**: sort alphabetically (case insensitive) by the displayed name
+* **".slug"**: sort alphabetically by the slug
+* **".bucket"**: sort by the difficulty bucket (easy, medium, hard)
+* **".bucket, .slug"**: sort by the difficulty bucket then by slug
+* **".difficulty"**: sort by the difficulty value (1, 2, 3, ... 10)
+* **".difficulty, .name"**: sort by the difficulty then by name
+* **".difficulty, .slug"**: sort by the difficulty then by slug
+
+### Example
+
+```yaml
+name: Exercise order
+
+on:
+  pull_request:
+    branches:
+      - main
+
+permissions:
+  contents: read
+
+jobs:
+  call-gha-workflow:
+    name: check
+    uses: exercism/github-actions/.github/workflows/sorted.yml@main
+    with:
+      ordering: ".bucket, .slug"
+```
+
 [configlet]: https://exercism.org/docs/building/configlet
 [configlet-lint]: https://exercism.org/docs/building/configlet/lint