[ty] Model walrus bindings from comprehensions#26466
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Typing conformance resultsNo changes detected ✅Current numbersThe percentage of diagnostics emitted that were expected errors held steady at 94.47%. The percentage of expected errors that received a diagnostic held steady at 89.19%. The number of fully passing files held steady at 95/134. |
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core (https://github.com/home-assistant/core)
- homeassistant/components/ista_ecotrend/sensor.py:277:47 error[unresolved-reference] Name `statistics_sum` used when not defined
- homeassistant/components/recorder/history/__init__.py:909:53 error[unresolved-reference] Name `prev_state` used when not defined
- homeassistant/components/recorder/history/__init__.py:925:49 error[unresolved-reference] Name `prev_state` used when not defined
mkosi (https://github.com/systemd/mkosi)
- mkosi/__init__.py:5249:80 error[unresolved-reference] Name `c` used when not defined
- mkosi/__init__.py:5254:79 error[unresolved-reference] Name `c` used when not defined
- mkosi/config.py:4776:41 error[unresolved-reference] Name `missing` used when not defined
steam.py (https://github.com/Gobot1234/steam.py)
- steam/_gc/client.py:56:90 error[unresolved-reference] Name `previous_state` used when not defined
xarray (https://github.com/pydata/xarray)
- xarray/core/extension_array.py:154:16 error[unresolved-reference] Name `ea_type` used when not defined
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## Summary This separates constructing and registering a `Definition` from recording it in the current scope's use-def state. `push_additional_definition` continues to create and associate AST-backed definitions, then delegates the existing binding, declaration, capture, and try-context bookkeeping to `record_definition`. This is a behavior-neutral refactor split from #26466 so synthesized definitions can reuse the recording path without mixing the mechanical extraction into the comprehension-walrus change. The ty core and semantic suites and repository hooks pass.
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Summary
PEP 572 specifies that an assignment-expression target inside a comprehension binds in the scope containing the outermost comprehension. Before this change, we left the target inside the comprehension scope, so it was unresolved when referenced afterward. For example, these two cases raised false positives on
main:This PR makes the walrus target visible in the containing scope while keeping its value expression in the comprehension scope, where it can reference iteration variables.
What's included vs. excluded
I went through several iterations of this change over the past few months, and each time they ballooned in scope. Here, I'm trying to intentionally limit the scope, so this section articulates cases that came up in Codex review but were explicitly rejected as out-of-scope.
We do not model the zero-iteration path or whether a generator expression has been consumed:
We also conservatively promote exported values because later iterations can change them. We do not try to retain single-iteration literal precision:
We do not compute a fixed point for a walrus whose value changes type across repeated iterations. We currently infer the exported type from the first modeled iteration:
(This requires treating the comprehension body as a loop and iterating its use-def state to a fixed point.)
We also defer all the IDE-specific navigation, references, rename, and unused-binding behavior to a separate PR (#26476).
Closes astral-sh/ty#162.