Step alias rendering raises SyntaxError when the step's if condition is false

[ausias-armesto]

Step alias rendering raises SyntaxError when the step's if condition is false

Description

When a step defines both an alias block and an if condition, the alias
expressions are currently rendered before the if condition is
evaluated. If the step is meant to be skipped (its if evaluates to
false) and one of its alias expressions references the result of another
step that was itself skipped (and therefore has no result in the
context), rendering that alias produces broken output — e.g. a template
like:

keep.dictget({{ steps.get-incident.results.body }}, 'user_generated_name', 'Untitled incident')

renders steps.get-incident.results.body as an empty string, turning
the expression into the syntactically invalid keep.dictget(, 'user_generated_name', 'Untitled incident').

This raises a SyntaxError and aborts the workflow step entirely,
instead of the step being cleanly skipped as the if condition intends.

Steps to reproduce

1. Define a step with an if condition that evaluates to false because
   it depends on the result of another step that was skipped.
2. Give that step an alias whose expression references the same
   skipped step's result.
3. Run the workflow.

Expected behavior

The step should be skipped without error — aliases should only be
evaluated once it's known the step will actually run.

Actual behavior

A SyntaxError is raised while rendering the alias expression, because
it's evaluated unconditionally before the if check.

Relevant code

keep/step/step.py, in Step._run_single — aliases are rendered and set
into the context near the top of the method, before the if condition
is checked further down.

[dosubot]

@ausias-armesto, confirmed — the code does exactly what you described. In _run_single, aliases are rendered and pushed into the context at lines 161–169, while the if condition isn't evaluated until lines 219–267. There's no early return between the two, so alias rendering always runs — even for steps whose if will evaluate to false.

The failure mechanism matches too: when io_handler.render hits a reference to a skipped step's result, it substitutes an empty string, so something like keep.dictget({{ steps.get-incident.results.body }}, 'user_generated_name', 'Untitled incident') becomes the syntactically invalid keep.dictget(, 'user_generated_name', 'Untitled incident'). That SyntaxError fires before the if check at line 270 ever gets to short-circuit and skip the step.

The fix — moving alias rendering (lines 161–169) to after evaluated_if_met is determined and the early return on if not evaluated_if_met (line 279) — looks correct and minimal. One thing worth verifying: the if block's own condition evaluation (lines 219–267) doesn't appear to depend on the step's alias: map being set first (it uses condition.condition_alias from the condition: block, which is separate), so reordering should be safe. But it's worth double-checking that no existing workflow has an if expression that references {{ alias.x }} from the same step's own alias: block — if any do, they'd break after the move.

Would you be interested in opening a PR for this?

To reply, just mention @dosu.

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