document empty overrides, exclude and ignored_validations (#33)

* document optional `overrides`, `exclude` and `ignored_validations`

* add test

* Apply suggestions from code review

Co-authored-by: Justus Magin <keewis@users.noreply.github.com>

---------

Co-authored-by: Justus Magin <keewis@users.noreply.github.com>

Author: mathause

.github/workflows/ci.yml

@@ -50,14 +50,20 @@ jobs:
             envs/env1.yaml
             envs/env2.yaml
         expected-failure: ["false"]
+        policy-file: ["policy.yaml"]
         include:
           - env-paths: |
               envs/failing-env1.yaml
+            policy-file: "policy.yaml"
             expected-failure: "true"
           - env-paths: |
               envs/env1.yaml
               envs/failing-env1.yaml
+            policy-file: "policy.yaml"
             expected-failure: "true"
+          - env-paths: "envs/env1.yaml"
+            policy-file: policy_no_extra_options.yaml
+            expected-failure: "false"
 
     steps:
       - name: clone the repository
@@ -67,7 +73,7 @@ jobs:
         id: action-run
         continue-on-error: true
         with:
-          policy: policy.yaml
+          policy: ${{ matrix.policy-file }}
           environment-paths: ${{ matrix.env-paths }}
           today: 2024-12-20
       - name: detect outcome

README.md

@@ -32,7 +32,17 @@ policy:
     - package4
 ```
 
-then add a new step to CI:
+If there are no packages with `overrides`, `exclude`, or `ignored_violations`, you can set
+them to an empty mapping or sequence, respectively:
+
+```yaml
+  ...
+  overrides: {}
+  exclude: []
+  ignored_violations: []
+```
+
+Then add a new step to CI:
 
 ```yaml
 jobs:

policy_no_extra_options.yaml

@@ -0,0 +1,14 @@
+channels:
+  - conda-forge
+platforms:
+  - noarch
+  - linux-64
+policy:
+  # all packages in months
+  packages:
+    python: 30
+    numpy: 18
+  default: 12
+  overrides: {}
+  exclude: []
+  ignored_violations: []