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Lambda with default params is not recognized in missing-argument checks #2612

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Lambda with default params is not recognized in missing-argument checks#2612
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grievejia
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typecheckingusabilityUsability & readiness issues identified with running Pyrefly on top OSS projects
@grievejia

Description

@grievejia
grievejia
opened on Mar 2, 2026

Describe the Bug

Minimal repro:

# Pyrefly does not recognize default parameter values in lambda
# expressions, so calling a lambda without the defaulted argument
# triggers a missing-argument error.
solver = lambda f, x, domain="reals": f(x)
result = solver(abs, -5)  # FP: pyrefly reports missing argument 'domain'

Sandbox Link

https://pyrefly.org/sandbox/?project=N4IgZglgNgpgziAXKOBDAdgEwEYHsAeAdAA4CeSIAxAAQAKpATjGFKdZrvNergC7VMAxrgDm6CAC8Y7ZqgCuUfsVQNUAWxi8YDagDdUUOVwjpqUddkyoAOuhox8xJnDgRc6OABpqcXNUEGUCYi1KhmFlbUAO4QvAAWuHL88dKYsgpamKEMInIa6Ly2NLwMECIi2nCh1GoQLsEAtCq5%2BfzaDLgMhLa%2BULra1AC84WqWYWDe%2BN4caqgmg9YgTAZwi4jUYAAU%2BACUts4ZQz64fdqbqNhe1A0ArDvU1DQAYrTrZEwsbEzEnbxVtfV0CFmnkYAVqAByGZzdAQ6ggTwgJLQOAkciIKjUACqvGgsTYYDk6EEuPcq3QtjSYA2nVmvAA%2Bug8tgzvh1iZePcGgA%2BHwlRC2B4PJi8OQMUxgRYAOWZ2nWwHwAF9FrYESB3sxWIReLg1FAKDR6B9WD4MDgCP53JBcqpSehunZqABlGDSOK8XjEOCIAD0Po1n0InREPrBPo4gjgPuE6GtYtQdp9NJ0qH00AusEtsbK8bt1FwxDtqNsZHi7ga-QYrncR0WAGZCABGABMKvQIEViNQJIg-Se0BgFDQWDwRDIHaAA

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typecheckingusabilityUsability & readiness issues identified with running Pyrefly on top OSS projects

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