[red-knot] Infer lambda expression
#16547
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AlexWaygood
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This looks great, thanks!
dhruvmanila
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Mar 10, 2025
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| let file = input.file(db); | ||
| let _span = tracing::trace_span!( | ||
| "infer_definition_types_cycle_recovery", | ||
| range = ?input.kind(db).target_range(), | ||
| file = %file.path(db) | ||
| ) | ||
| .entered(); | ||
|
|
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This is similar to infer_definition_types and it allowed me to quickly understand the origin of the cycle and what was causing it.
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As we discussed in 1:1, we can infer a return type in some cases if we make default values of the parameters standalone expressions, so they can be resolved without creating a cycle. Longer term, we may want to do "inlining" of lambdas at their usage sites so we can do better transparent inference, but that's for later. |
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* main: [red-knot] Rework `Type::to_instance()` to return `Option<Type>` (#16428) [red-knot] Add tests asserting that `KnownClass::to_instance()` doesn't unexpectedly fallback to `Type::Unknown` with full typeshed stubs (#16608) [red-knot] Handle gradual intersection types in assignability (#16611) [red-knot] mypy_primer: split installation and execution (#16622) [red-knot] mypy_primer: pipeline improvements (#16620) [red-knot] Infer `lambda` expression (#16547) [red-knot] mypy_primer: strip ANSI codes (#16604) [red-knot] mypy_primer: comment on PRs (#16599)
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Summary
Part of #15382
This PR adds support for inferring the
lambdaexpression and return theCallableType.Currently, this is only limited to inferring the parameters and a todo type for the return type.
For posterity, I tried using the
file_expression_typeto infer the return type of lambda but it would always lead to cycle. The main reason is that ininfer_parameter_definition, the default expression is being inferred usingfile_expression_type, which is correct, but it thenTake the following source code as an example:
Here's how the code will flow:
infer_scope_typesfor the global scopeinfer_lambda_expressioninfer_expressionfor the default value1file_expression_typefor the return type using the body expression. This is because the body creates it's own scopeinfer_scope_types(lambda body scope)infer_name_loadfor the symbolxwhose visible binding is the lambda parameterxinfer_parameter_definitionfor parameterxfile_expression_typefor the default value1infer_scope_typesfor the global scope because of the default expressionThis will then reach to
infer_definitionfor the parameterxagain which then creates the cycle.Test Plan
Add tests around
lambdaexpression inference.