Allow -1 generation step index (#1342)

Summary: Pull Request resolved: #1342

Reviewed By: bernardbeckerman

Differential Revision: D42252297

fbshipit-source-id: 38305b09817fafa6508e5f0edfd3e563c721677b

ax/core/generator_run.py

@@ -134,8 +134,10 @@ def __init__(
  rather than to reproduce the conditions, in which this generator
  run was created.
  generation_step_index: Optional index of the generation step that produced
- this generator run. Applicable only if the genetator run was created
- via a generation strategy.
+ this generator run. Applicable only if the generator run was created
+ via a generation strategy (in which case this index should reflect the
+ index of generation step in a generation strategy) or a standalone
+ generation step (in which case this index should be ``-1``).
  candidate_metadata_by_arm_signature: Optional dictionary of arm signatures
  to model-produced candidate metadata that corresponds to that arm in
  this generator run.
@@ -193,8 +195,14 @@ def __init__(
  )
  self._candidate_metadata_by_arm_signature = candidate_metadata_by_arm_signature
 
- # Validate that generation step index is non-negative.
- assert generation_step_index is None or generation_step_index >= 0
+ # Validate that generation step index is either not set (not from generation
+ # strategy or ste), is non-negative (from generation step) or is -1 (from a
+ # standalone generation step that was not a part of a generation strategy).
+ assert (
+ generation_step_index is None # Not generation strategy/step
+ or generation_step_index == -1 # Standalone generation step
+ or generation_step_index >= 0 # Generation strategy
+ )
  self._generation_step_index = generation_step_index
 
  @property