Add groupby_as_dict filter (#2323)

* Add groupby_as_dict filter.

* Test all error cases.

tests/integration/targets/filter_groupby/aliases

@@ -0,0 +1,2 @@
+shippable/posix/group4
+skip/python2.6  # filters are controller only, and we no longer support Python 2.6 on the controller

tests/integration/targets/filter_groupby/tasks/main.yml

@@ -0,0 +1,45 @@
+---
+- name: Test functionality
+  assert:
+    that:
+      - list1 | community.general.groupby_as_dict('name') == dict1
+
+- name: 'Test error: not a list'
+  set_fact:
+    test: "{{ list_no_list | community.general.groupby_as_dict('name') }}"
+  ignore_errors: true
+  register: result
+
+- assert:
+    that:
+      - result.msg == 'Input is not a sequence'
+
+- name: 'Test error: list element not a mapping'
+  set_fact:
+    test: "{{ list_no_dict | community.general.groupby_as_dict('name') }}"
+  ignore_errors: true
+  register: result
+
+- assert:
+    that:
+      - "result.msg == 'Sequence element #0 is not a mapping'"
+
+- name: 'Test error: list element does not have attribute'
+  set_fact:
+    test: "{{ list_no_attribute | community.general.groupby_as_dict('name') }}"
+  ignore_errors: true
+  register: result
+
+- assert:
+    that:
+      - "result.msg == 'Attribute not contained in element #1 of sequence'"
+
+- name: 'Test error: attribute collision'
+  set_fact:
+    test: "{{ list_collision | community.general.groupby_as_dict('name') }}"
+  ignore_errors: true
+  register: result
+
+- assert:
+    that:
+      - result.msg == "Multiple sequence entries have attribute value 'a'"

tests/integration/targets/filter_groupby/vars/main.yml

@@ -0,0 +1,31 @@
+---
+list1:
+  - name: a
+    x: y
+  - name: b
+    z: 1
+
+dict1:
+  a:
+    name: a
+    x: y
+  b:
+    name: b
+    z: 1
+
+list_no_list:
+  a:
+    name: a
+
+list_no_dict:
+  - []
+  - 1
+
+list_no_attribute:
+  - name: a
+    foo: baz
+  - foo: bar
+
+list_collision:
+  - name: a
+  - name: a