Merge ~sylvain-pineau/checkbox-ng:special_functions_in_templates into checkbox-ng:master

[Sylvain Pineau]

Allow a combination of the template resource parameters and use of special functions such as __checkbox_env__ in templated jobs.

Use case developed in the checkbox-desktop snap where the resource creates jobs for each GTK theme but the snap channel is decided via config.:

unit: template
template-engine: jinja2
template-resource: gtk_theme
id: snaps/gnome-characters-{{ __checkbox_env__.get("SNAP_CHANNEL_GNOME_CHARACTERS", "stable") }}-{{ theme }}.jpg
plugin: attachment
depends: snaps/gnome-characters-{{ __checkbox_env__.get("SNAP_CHANNEL_GNOME_CHARACTERS", "stable") }}
command:
  [ -f $PLAINBOX_SESSION_SHARE/gnome-characters-{{ __checkbox_env__.get("SNAP_CHANNEL_GNOME_CHARACTERS", "stable") }}-{{ theme }}.jpg ] &&
  cat $PLAINBOX_SESSION_SHARE/gnome-characters-{{ __checkbox_env__.get("SNAP_CHANNEL_GNOME_CHARACTERS", "stable") }}-{{ theme }}.jpg

[Jonathan Cave (jocave)]

Why is a special function desirable for this purpose as opposed to being able to access a parameter from another resource (e.g. the environment resource)?

[Sylvain Pineau (sylvain-pineau)]

you cannot template from multiple resources

[Jonathan Cave (jocave)]

No you can't, but I don't understand why you should be allowed to do this as a workaround

[Sylvain Pineau (sylvain-pineau)]

Let's ignore this patch. Dropping the parameter from the id field (the one from __checkbox_env__) did it!

Unmerged commits

4506e0f... by Sylvain Pineau on 2020-08-21

validators: Allow a combination of template parameters and special functions

such as __checkbox_env__, __system_env__ and __on_ubuntucore__.

diff --git a/plainbox/impl/unit/validators.py b/plainbox/impl/unit/validators.py
index af027f8..da3d9d2 100644
--- a/plainbox/impl/unit/validators.py
+++ b/plainbox/impl/unit/validators.py
@@ -474,6 +474,9 @@ class TemplateVariantFieldValidator(FieldValidatorBase):
     parameter it references is defined in the particular unit being validated.
     """
 
+    _special_parameters = [
+        '__checkbox_env__', '__system_env__', '__on_ubuntucore__']
+
     def check(self, parent, unit, field):
         # Non-parametric units are always valid
         if unit.is_parametric:
@@ -491,6 +494,8 @@ class TemplateVariantFieldValidator(FieldValidatorBase):
                         unit, field, Problem.constant, self.message)
                 # Each parameter must be present in the unit
                 for param_name in param_set:
+                    if param_name in self._special_parameters:
+                        continue
                     if param_name not in unit.parameters:
                         message = _(
                             "reference to unknown parameter {!r}"