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Fix infinite recursion bug in .inherited sigs #1636

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21 changes: 15 additions & 6 deletions lib/tapioca/runtime/generic_type_registry.rb
Original file line number Diff line number Diff line change
Expand Up @@ -117,7 +117,7 @@ def create_generic_type(constant, name)
# the generic class `Foo[Bar]` is still a `Foo`. That is:
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^ Typo in commit message

# `Foo[Bar].new.is_a?(Foo)` should be true, which isn't the case
# if we just clone the class. But subclassing works just fine.
create_safe_subclass(constant)
create_safe_subclass(constant, name)
else
# This can only be a module and it is fine to just clone modules
# since they can't have instances and will not have `is_a?` relationships.
Expand Down Expand Up @@ -151,21 +151,30 @@ def create_generic_type(constant, name)
generic_type
end

sig { params(constant: T::Class[T.anything]).returns(T::Class[T.anything]) }
def create_safe_subclass(constant)
sig { params(constant: T::Class[T.anything], name: String).returns(T::Class[T.anything]) }
def create_safe_subclass(constant, name)
# Lookup the "inherited" class method
inherited_method = constant.method(:inherited)
# and the module that defines it
owner = inherited_method.owner

# If no one has overriden the inherited method yet, just subclass
# If no one has overridden the inherited method yet, just subclass
return Class.new(constant) if Class == owner

# Capture this Hash locally, to mutate it in the `inherited` callback below.
generic_instances = @generic_instances

begin
# Otherwise, some inherited method could be preventing us
# from creating subclasses, so let's override it and rescue
owner.send(:define_method, :inherited) do |s|
inherited_method.call(s)
owner.send(:define_method, :inherited) do |new_subclass|
# Register this new subclass ASAP, to prevent re-entry into the `create_safe_subclass` code-path.
# This can happen if the sig of the original `.inherited` method references the generic type itself.
generic_instances[name] ||= new_subclass
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Admittedly, this is a bit odd.

I would have preferred keeping the simplicity of the "create the thing, then register the thing" as two clean, separate steps, but I don't think that's possible.

Registering the "completed" subclass requires it to first be created, creating it entails running its sigs, which attempts to register it. 🔁

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You could separate the process in 2 steps. 1. to register the class and 2. to call the original .inherited. But this looks good enough 👍

Should we update the register_type comment to add a note about recursiveness?


# Call the original `.inherited` method, but rescue any errors that might be raised,
# which would have otherwise prevented our subclass from being created.
inherited_method.call(new_subclass)
rescue
# Ignoring errors
end
Expand Down
42 changes: 42 additions & 0 deletions spec/tapioca/runtime/generic_type_registry_spec.rb
Original file line number Diff line number Diff line change
Expand Up @@ -77,6 +77,17 @@ class GenericTypeRegistrySpec < Minitest::Spec
refute_same(result, RaisesInInheritedCallback)
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^ There is a typo in the commit message

assert_operator(result, :<, RaisesInInheritedCallback)
end

it "works for classes that specify a 'loose' sig on .inherited" do
# By "loose", we mean `T::Class[T.anything]` instead of `T::Class[SampleGenericClass[T.anything]]`
_ = HasNonRecursiveInheritedSig[Object]
end

it "works for classes whose .inherited sig reference the generic type itself" do
# Our swizzled implementation of the `.inherited` method needs to be carefully implemented to not fall into
# infinite recursion when the sig for the method references the class that it's defined on.
_ = HasRecursiveInheritedSig[Object]
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end
end
end

Expand All @@ -98,6 +109,37 @@ def inherited(subclass)
end
end
end

class HasNonRecursiveInheritedSig
extend T::Generic

Element = type_member

class << self
extend T::Sig

sig { params(subclass: T::Class[T.anything]).void }
def inherited(subclass)
super
end
end
end

class HasRecursiveInheritedSig
extend T::Generic

Element = type_member

class << self
extend T::Sig

# This sig references an instantiation of this class itself.
sig { params(subclass: T::Class[HasRecursiveInheritedSig[T.anything]]).void }
def inherited(subclass)
super
end
end
end
end
end
end