Disallow duplicate site keys within a host's wordpress_sites (#910)

If a user loads both staging and production sites on a single host,
site keys must differ between environments to prevent conflict
that would otherwise occur in resources built from site keys
(e.g., Nginx conf filepaths).

CHANGELOG.md

@@ -1,4 +1,5 @@
 ### HEAD
+* Disallow duplicate site keys within a host's `wordpress_sites` ([#910](https://github.com/roots/trellis/pull/910))
 * Fix `raw_vars` functionality for Ansible 2.4.1 ([#915](https://github.com/roots/trellis/pull/915))
 * Enable Virtualbox ioapic option ([#913](https://github.com/roots/trellis/pull/913))
 * Dynamically increase `ansible_group_priority` for selected env ([#909](https://github.com/roots/trellis/pull/909))

roles/common/defaults/main.yml

@@ -1,5 +1,25 @@
 ntp_timezone: Etc/UTC
 
+env_groups: "{{ ['development', 'staging', 'production'] | intersect(group_names) }}"
+
+envs_with_wp_sites: "{{
+  lookup('filetree', playbook_dir + '/group_vars') |
+  selectattr('path', 'match', '(' + env_groups | join('|') + ')/wordpress_sites\\.yml$') |
+  map(attribute='path') | map('regex_replace', '([^/]*)/.*', '\\1') | list
+}}"
+
+site_keys_by_env_pair: "[
+  {% for env_pair in envs_with_wp_sites | combinations(2) | list %}
+    {
+      'env_pair': {{ env_pair }},
+      'site_keys': {{
+                     (vars[env_pair[0] + '_sites'].wordpress_sites | default({})).keys() | intersect(
+                     (vars[env_pair[1] + '_sites'].wordpress_sites | default({})).keys())
+                   }}
+    },
+  {% endfor %}
+]"
+
 apt_packages_default:
   python-software-properties: "{{ apt_package_state }}"
   python-pycurl: "{{ apt_package_state }}"

roles/common/tasks/main.yml

@@ -1,4 +1,26 @@
 ---
+- block:
+  - name: Load wordpress_sites.yml vars into <env>_sites vars
+    include_vars:
+      file: group_vars/{{ item }}/wordpress_sites.yml
+      name: "{{ item }}_sites"
+    with_items: "{{ envs_with_wp_sites }}"
+    when: envs_with_wp_sites | count > 1
+
+  - name: Fail if there are duplicate site keys within host's wordpress_sites
+    fail:
+      msg: >
+        If you put multiple environments on `{{ inventory_hostname }}`, `wordpress_sites`
+        must use different site keys per environment. Adjust the following site keys that
+        are duplicated between the `{{ item.env_pair | join('` and `') }}` groups:
+          {{ item.site_keys | to_nice_yaml | indent(2) }}
+    when: item.site_keys | count
+    with_items: "{{ site_keys_by_env_pair }}"
+
+  when:
+    - env_groups | count > 1
+    - validate_site_keys | default(true) | bool
+
 - name: Validate wordpress_sites
   fail:
     msg: "{{ lookup('template', 'wordpress_sites.j2') }}"