template: fix KeyError: 'undefined variable: 0 (#27972)

* template: fix KeyError: 'undefined variable: 0

For compatibility with the Context.get_all() implementation
in jinja 2.9, make AnsibleJ2Vars implement collections.Mapping.
Also, make AnsibleJ2Template.newcontext() handle dict type
for the 'vars' parameter.

See: d67f0fd4cc
Fixes: https://github.com/ansible/ansible/issues/20494

* add units/template/test_vars

* intg tests for jinja-2.9 issues like 20494

test cases here are based on
https://github.com/ansible/ansible/issues/20494#issue-202108318

test/integration/targets/template/files/import_as.expected

@@ -0,0 +1,3 @@
+hello world import as
+WIBBLE
+Goodbye

test/integration/targets/template/files/import_as_with_context.expected

@@ -0,0 +1,2 @@
+hello world as qux with context
+WIBBLE

test/integration/targets/template/files/import_with_context.expected

@@ -0,0 +1,3 @@
+hello world with context
+WIBBLE
+Goodbye

test/integration/targets/template/tasks/main.yml

@@ -51,6 +51,60 @@
     that: 
       - "template_result.changed == true"
 
+# test for import with context on jinja-2.9 See https://github.com/ansible/ansible/issues/20494
+- name: fill in a template using import with context ala issue 20494
+  template: src=import_with_context.j2 dest={{output_dir}}/import_with_context.templated mode=0644
+  register: template_result
+
+- name: copy known good import_with_context.expected into place
+  copy: src=import_with_context.expected dest={{output_dir}}/import_with_context.expected
+
+- name: compare templated file to known good import_with_context
+  shell: diff -uw {{output_dir}}/import_with_context.templated {{output_dir}}/import_with_context.expected
+  register: diff_result
+
+- name: verify templated import_with_context matches known good
+  assert:
+    that:
+        - 'diff_result.stdout == ""'
+        - "diff_result.rc == 0"
+
+# test for 'import as' on jinja-2.9 See https://github.com/ansible/ansible/issues/20494
+- name: fill in a template using import as ala fails2 case in issue 20494
+  template: src=import_as.j2 dest={{output_dir}}/import_as.templated mode=0644
+  register: import_as_template_result
+
+- name: copy known good import_as.expected into place
+  copy: src=import_as.expected dest={{output_dir}}/import_as.expected
+
+- name: compare templated file to known good import_as
+  shell: diff -uw {{output_dir}}/import_as.templated {{output_dir}}/import_as.expected
+  register: import_as_diff_result
+
+- name: verify templated import_as matches known good
+  assert:
+    that:
+        - 'import_as_diff_result.stdout == ""'
+        - "import_as_diff_result.rc == 0"
+
+# test for 'import as with context' on jinja-2.9 See https://github.com/ansible/ansible/issues/20494
+- name: fill in a template using import as with context ala fails2 case in issue 20494
+  template: src=import_as_with_context.j2 dest={{output_dir}}/import_as_with_context.templated mode=0644
+  register: import_as_with_context_template_result
+
+- name: copy known good import_as_with_context.expected into place
+  copy: src=import_as_with_context.expected dest={{output_dir}}/import_as_with_context.expected
+
+- name: compare templated file to known good import_as_with_context
+  shell: diff -uw {{output_dir}}/import_as_with_context.templated {{output_dir}}/import_as_with_context.expected
+  register: import_as_with_context_diff_result
+
+- name: verify templated import_as_with_context matches known good
+  assert:
+    that:
+        - 'import_as_with_context_diff_result.stdout == ""'
+        - "import_as_with_context_diff_result.rc == 0"
+
 # VERIFY CONTENTS
 
 - name: check what python version ansible is running on

test/integration/targets/template/templates/bar

@@ -0,0 +1 @@
+Goodbye

test/integration/targets/template/templates/import_as.j2

@@ -0,0 +1,4 @@
+{% import 'qux' as qux %}
+hello world import as
+{{ qux.wibble }}
+{% include 'bar' %}

test/integration/targets/template/templates/import_as_with_context.j2

@@ -0,0 +1,3 @@
+{% import 'qux' as qux with context %}
+hello world as qux with context
+{{ qux.wibble }}

test/integration/targets/template/templates/import_as_with_context.js

@@ -0,0 +1,3 @@
+{% import 'qux' as qux with context %}
+hello world as qux with context
+{{ qux.wibble }}

test/integration/targets/template/templates/import_with_context.j2

@@ -0,0 +1,4 @@
+{% import 'qux' as qux with context %}
+hello world with context
+{{ qux.wibble }}
+{% include 'bar' %}

test/integration/targets/template/templates/qux

@@ -0,0 +1 @@
+{% set wibble = "WIBBLE" %}