feat: include alias path when generating template (elastic#877)

# Conflicts:
#	CHANGELOG.next.md

CHANGELOG.next.md

@@ -28,6 +28,9 @@ Thanks, you're awesome :-) -->
 
 #### Added
 
+* Added ability to supply free-form usage documentation per fieldset. #988
+* Added the `path` key when type is `alias`, to support the [alias field type](https://www.elastic.co/guide/en/elasticsearch/reference/current/alias.html). #877
+
 #### Improvements
 
 #### Deprecated

schemas/README.md

@@ -151,6 +151,18 @@ Supported keys to describe expected values for a field
   Optionally, entries in this list can specify 'expected\_event\_types'.
 - expected\_event\_types: list of expected "event.type" values to use in association
   with that category.
+
+Supported keys when using the [alias field type](https://www.elastic.co/guide/en/elasticsearch/reference/current/alias.html)
+
+```YAML
+    - name: a_field
+      level: extended
+      type: alias
+      path: another_field
+      description: >
+        An alias of another field.
+```
+- path (optional): The full path to the [aliases' target field](https://www.elastic.co/guide/en/elasticsearch/reference/current/alias.html#alias-targets).
 
 #### Multi\_fields
 

scripts/generators/beats.py

@@ -34,7 +34,7 @@ def fieldset_field_array(source_fields, df_whitelist, fieldset_prefix):
     allowed_keys = ['name', 'level', 'required', 'type', 'object_type',
                     'ignore_above', 'multi_fields', 'format', 'input_format',
                     'output_format', 'output_precision', 'description',
-                    'example', 'enabled', 'index']
+                    'example', 'enabled', 'index', 'path']
     multi_fields_allowed_keys = ['name', 'type', 'norms', 'default_field', 'normalizer', 'ignore_above']
 
     fields = []

scripts/generators/es_template.py

@@ -59,6 +59,8 @@ def entry_for(field):
             ecs_helpers.dict_copy_existing_keys(field, field_entry, ['ignore_above'])
         elif field['type'] == 'text':
             ecs_helpers.dict_copy_existing_keys(field, field_entry, ['norms'])
+        elif field['type'] == 'alias':
+            ecs_helpers.dict_copy_existing_keys(field, field_entry, ['path'])
 
         if 'multi_fields' in field:
             field_entry['fields'] = {}

scripts/schema/cleaner.py

@@ -158,6 +158,12 @@ def field_mandatory_attributes(field):
         return
     current_field_attributes = sorted(field['field_details'].keys())
     missing_attributes = ecs_helpers.list_subtract(FIELD_MANDATORY_ATTRIBUTES, current_field_attributes)
+
+    # The `alias` type requires a target path.
+    # https://github.com/elastic/ecs/issues/876
+    if field['field_details'].get('type') == 'alias' and 'path' not in current_field_attributes:
+        missing_attributes.append('path')
+
     if len(missing_attributes) > 0:
         msg = "Field is missing the following mandatory attributes: {}.\nFound these: {}.\nField details: {}"
         raise ValueError(msg.format(', '.join(missing_attributes),

scripts/tests/test_es_template.py

@@ -109,6 +109,19 @@ def test_entry_for_index(self):
         }
         self.assertEqual(es_template.entry_for(test_map), exp)
 
+    def test_entry_for_alias(self):
+        test_map = {
+            'name': 'test.alias',
+            'type': 'alias',
+            'path': 'alias.target'
+        }
+
+        exp = {
+            'type': 'alias',
+            'path': 'alias.target'
+        }
+        self.assertEqual(es_template.entry_for(test_map), exp)
+
 
 if __name__ == '__main__':
     unittest.main()

scripts/tests/unit/test_schema_cleaner.py

@@ -157,6 +157,13 @@ def test_field_raises_on_missing_required_attributes(self):
                                         "mandatory attributes: {}".format(missing_attribute)):
                 cleaner.field_mandatory_attributes(field)
 
+    def test_field_raises_on_alias_missing_path_attribute(self):
+        field = self.schema_process()['process']['fields']['pid']
+        field['field_details']['type'] = "alias"
+        with self.assertRaisesRegex(ValueError,
+                                    "mandatory attributes: {}".format("path")):
+            cleaner.field_mandatory_attributes(field)
+
     def test_field_simple_cleanup(self):
         my_field = {
             'field_details': {