branching pipeline in YAML

[droumis]

ALL software version info

lumen 0.5.0a64

Description of expected behavior and the observed behavior

I'm trying to branch a pipeline in YAML. I may be misunderstanding the API, but I would have expected the code below to run. The traceback is complaining about the pipeline branch ('branch_sort') not having a 'source'... but it should be inheriting the source from the pipeline that it's branching from.

Complete, minimal, self-contained example code that reproduces the issue

sources:
  penguin_source:
    type: file
    tables:
      penguin_table: https://raw.githubusercontent.com/rfordatascience/tidytuesday/master/data/2020/2020-07-28/penguins.csv

pipelines:
  penguin_pipeline:
    source: penguin_source
    table: penguin_table
    filters:
      - type: widget
        field: island
  branch_sort:
    pipeline: penguin_pipeline
    transforms:
      - type: columns
        columns: ['species', 'island', 'bill_length_mm', 'bill_depth_mm']

targets:
  - title: Penguins
    sizing_mode: stretch_width
    views:
      - type: table
        pipeline: penguin_pipeline
        show_index: false
        height: 300
      - type: table
        pipeline: branch_sort
        show_index: false
        height: 300

Stack traceback

lumen serve penguin.yml

KeyError: 'source'
Traceback (most recent call last):
  File "/Users/droumis/src/lumen/lumen/dashboard.py", line 362, in _render_dashboard
    self._materialize_specification()
  File "/Users/droumis/src/lumen/lumen/dashboard.py", line 407, in _materialize_specification
    state.load_pipelines(auto_update=self.config.auto_update)
  File "/Users/droumis/src/lumen/lumen/state.py", line 161, in load_pipelines
    for name, source_spec in self.spec.get('pipelines', {}).items()
  File "/Users/droumis/src/lumen/lumen/state.py", line 161, in <dictcomp>
    for name, source_spec in self.spec.get('pipelines', {}).items()
  File "/Users/droumis/src/lumen/lumen/pipeline.py", line 221, in from_spec
    source = spec['source']
KeyError: 'source'

[droumis]

It seems that the transform on the pipeline branch is not being applied to the view that references it. In the image below, I would expect to see only the selected columns (['species', 'island', 'bill_length_mm', 'bill_depth_mm']) in the second table. This is using the same example script from the original comment above.

[github-actions]

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