sphinx-needs master throws warning needs.filter on seemingly valid filter function

[arwedus]

Hi all!

given this document:

.. needpie:: System Requirement Status
   :legend:
   :text_color: w
   :labels: draft, assumed, rejected
   :explode: 0, 0.3, 0

   id.startswith("REQ_SYS_DC_") and status == 'draft'
   id.startswith("REQ_SYS_DC_") and status == 'assumed'
   id.startswith("REQ_SYS_DC_") and status == 'rejected'


.. needpie:: System Requirements linked to Feature
   :legend:
   :text_color: w
   :labels: linked, unlinked
   :explode: 0.3, 0.0

   id.startswith("REQ_SYS_DC_") and status not in "rejected" and derives
   id.startswith("REQ_SYS_DC_") and status not in "rejected" and not derives

Requirement without links
-------------------------

.. req-sys:: DC Configuration Availability
   :id: REQ_SYS_DC_0001
   :status: assumed

   The subsystem shall maintain its configuration across ignition cycles.

Trigger Actions
---------------

.. req-sys:: DC Trigger Debounce
   :id: REQ_SYS_DC_0002
   :status: assumed
   :derives: FEATURE_DC_SW_CRASHES

   The subsystem shall provide a mechanism to debounce detections of the same trigger.

.. req-sys:: DC Trigger Action
   :id: REQ_SYS_DC_0003
   :status: assumed
   :derives: FEATURE_DC_RECOMPUTE_ACTIVITY
   
   The subsystem shall provide a trigger action called ...

I get this warning with sphinx-needs master:

system_requirements/index.rst:122: WARNING: Filter 'id.startswith("REQ_SYS_DC_") and status not in "rejected" and derives' not valid. Error: Filter did not evaluate to a boolean, instead <class 'list'>: ['REQ_SYS_DC_FFI']. [needs.filter]

The needpie filters used to do just what the author expected: Show a pie diagram with number of requirements which have a ":derives:" link vs. number of requirements having no ":derives:" link.

Indeed, the shown needpie is wrong. The filter condition must be changed to:

.. needpie:: System Requirements linked to Feature
   :legend:
   :text_color: w
   :labels: linked, unlinked
   :explode: 0.3, 0.0

   id.startswith("REQ_SYS_DC_") and da_status not in "rejected" and len(derives) > 0
   id.startswith("REQ_SYS_DC_") and da_status not in "rejected" and len(derives) == 0

Question: Why? Looks like a subtle incompatibility in the sphinx filter "API".

[danwos]

derives contains links, so it is a list, for instance ["my_link", "another_link"].
Checking for derives in a filters-string or python-statement will return the list and not a boolean interpretation (as it does when it gets checked in an if statement).

You can check this directly via python:

Also please be aware that da_status not in "rejected" is checking for a single character, not the complete string. So da_status = "c" would return False here.
da_status not in ["rejected",] would be safer :)