source-academy / py-slang / 30788832906

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Commit Message

Stepper: support a subset of module imports (#386)

* Make the Python stepper handle a subset of module imports (#385)

`from X import Y` used to make the stepper report "Evaluation stuck"
the instant it saw the import line, regardless of whether the
imported name was ever used. This wires up real module resolution
for the substitution stepper, mirroring the CSE machine's own
two-phase (load-then-run) model:

- FromImport now translates to a no-op statement instead of an inert
  placeholder identifier, rendering the student's actual import text.
- New OpaqueValue/ModuleFunction StepNode kinds represent opaque
  module handles and imported callables as legitimate, substitutable
  values.
- ModuleLoaderRunnerPlugin is registered on PyStepperEvaluatorBase,
  exactly as the CSE/py2js/Pvml evaluators already do.
- moduleInterop.ts resolves and substitutes a program's imports
  before stepping begins, and calls imported functions (trying the
  synchronous closure_call_sync fast path first, falling back to
  draining the async closure_call_unchecked generator). A Python
  closure passed as an argument into a module call is declined —
  that stays an honest "Evaluation stuck", the same degrade input()
  already gets — since supporting it would require re-entering the
  reducer's own step machinery mid-call.
- reduce.ts/getSteps.ts are now async end-to-end to support this.

Verified with integration tests against a fake module (the same
GenericDataHandler + ModuleLoaderRunnerPlugin harness
py2js-from-import.test.ts uses), not just the no-evaluator-wired
degrade path.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017w4FqCep4j8XyFpF4kpVue

* Address CodeRabbit review on #386

- moduleInterop.ts: use Promise.allSettled (not Promise.all) when
  requesting a program's modules, so a second rejection is observed
  instead of becoming an unhandled rejection racing the first one's
  throw. Preserve the loader's ... (continued)

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2 existing lines in 2 files now uncovered.

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