ignore errors rule docs (#2413)

src/ansiblelint/rules/ignore_errors.md

@@ -0,0 +1,61 @@
+# ignore-errors
+
+This rule checks that playbooks do not use the `ignore_errors` directive to ignore all errors.
+Ignoring all errors in a playbook hides actual failures, incorrectly mark tasks as failed, and result in unexpected side effects and behavior.
+
+Instead of using the `ignore_errors: true` directive, you should do the following:
+
+- Ignore errors only when using the `{{ ansible_check_mode }}` variable.
+- Use `register` to register errors.
+- Use `failed_when:` and specify acceptable error conditions.
+
+## Problematic Code
+
+```yaml
+---
+- name: Example playbook
+  hosts: all
+  tasks:
+    - name: Run apt-get update
+      ansible.builtin.command: apt-get update
+      ignore_errors: true # <- Ignores all errors, including important failures.
+```
+
+## Correct Code
+
+```yaml
+---
+- name: Example playbook
+  hosts: all
+  tasks:
+    - name: Run apt-get update
+      ansible.builtin.command: apt-get update
+      ignore_errors: "{{ ansible_check_mode }}" # <- Ignores errors in check mode.
+```
+
+```yaml
+---
+- name: Example playbook
+  hosts: all
+  tasks:
+    - name: Run apt-get update
+      ansible.builtin.command: apt-get update
+      ignore_errors: true
+      register: ignore_errors_register # <- Stores errors and failures for evaluation.
+```
+
+```yaml
+---
+- name: Example playbook
+  hosts: all
+  tasks:
+    - name: Disable apport
+      become: "yes"
+      lineinfile:
+        line: "enabled=0"
+        dest: /etc/default/apport
+        mode: 0644
+        state: present
+      register: default_apport
+      failed_when: default_apport.rc !=0 and not default_apport.rc == 257 # <- Defines conditions that constitute a failure.
+```