Show the available variable in the help text

Signed-off-by: Roberto Rosario <roberto.rosario@mayan-edms.com>

HISTORY.rst

@@ -13,6 +13,8 @@
 - Don't show the edit and delete links for resolved web links.
 - Exclude Smart link setup columns and links from the resolved
   smart link views.
+- TemplateField shows the available variable in the help text
+  automatically.
 
 3.3.4 (2019-12-09)
 ==================

mayan/apps/templating/fields.py

@@ -19,10 +19,13 @@ class TemplateField(forms.CharField):
         self.help_text = string_concat(
             self.initial_help_text, ' ',
             _(
-                'The template string to be evaluated. '
                 'Use Django\'s default templating language '
-                '(https://docs.djangoproject.com/en/%(django_version)s/ref/templates/builtins/)'
-            ) % {'django_version': mayan.__django_version__}
+                '(https://docs.djangoproject.com/en/%(django_version)s/ref/templates/builtins/). '
+                'The {{ %(variable)s }} variable is available to the template.'
+            ) % {
+                'django_version': mayan.__django_version__,
+                'variable': self.model_variable
+            }
         )
         self.widget.attrs['model'] = self.model
         self.widget.attrs['data-model-variable'] = self.model_variable

mayan/apps/templating/forms.py

@@ -19,6 +19,7 @@ class DocumentTemplateSandboxForm(forms.Form):
         self.model_variable = kwargs.pop('model_variable')
         super(DocumentTemplateSandboxForm, self).__init__(*args, **kwargs)
         self.fields['template'] = TemplateField(
+            initial_help_text=_('The template string to be evaluated.'),
             label=_('Template'), model=self.model,
             model_variable=self.model_variable, required=False
         )