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Fix nullability of GraphQL scalar types when passed as required arguments #2618

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KaanOzkan merged 2 commits into from
May 14, 2026
+42 −1
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Fix nullability of GraphQL scalar types when passed as required arguments #2618

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e265dd6
Fix nullability of GraphQL scalar types when passed as required argum…
joeytepp May 8, 2026
57bdcab
Add comment explaining non_nilable type wrapping
joeytepp May 13, 2026
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4 changes: 3 additions & 1 deletion lib/tapioca/dsl/helpers/graphql_type_helper.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -80,7 +80,9 @@ def type_for(type, ignore_nilable_wrapper: false, prepare_method: nil)
signature = Runtime::Reflection.signature_of(method)
return_type = signature&.return_type

valid_return_type?(return_type) ? return_type.to_s : "T.untyped"
# Wrap as non-nilable for required arguments. `coerce_input` supports both
# required and optional; optional arguments are re-wrapped below based on `type.non_null?`
valid_return_type?(return_type) ? RBIHelper.as_non_nilable_type(return_type.to_s) : "T.untyped"
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@KaanOzkan KaanOzkan May 11, 2026

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Can you give context on why we can assume coerce_input can't return nil?

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@joeytepp joeytepp May 11, 2026

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coerce_input has to handle both required and optional arguments, and for an optional argument it still gets called with an input of nil. So when we have a required argument the signature should no longer have a T.nilable(...) since we know the output won't be nil.

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@KaanOzkan KaanOzkan May 11, 2026 •
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Let's capture this in a comment since there's quite a bit going on, something like

# Wrap as non-nilable for required arguments. `coerce_input` supports both
# required and optional; optional arguments are re-wrapped below based on `type.non_null?`

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@joeytepp joeytepp May 13, 2026

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Great, I've updated it with the comment as suggested.

when GraphQL::Schema::InputObject.singleton_class
type_for_constant(unwrapped_type)
when Module
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39 changes: 39 additions & 0 deletions spec/tapioca/dsl/compilers/graphql_mutation_spec.rb
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Expand Up @@ -361,6 +361,45 @@ def resolve(loaded_argument:, loaded_arguments:, custom_name:, optional_loaded_a
assert_equal(expected, rbi_for(:CreateComment))
end

it "generates correct RBI for custom scalars whose coerce_input returns a nilable type" do
add_ruby_file("create_comment.rb", <<~RUBY)
class CustomScalar; end

class NilableScalarType < GraphQL::Schema::Scalar
class << self
extend T::Sig

sig { params(value: T.untyped, context: GraphQL::Query::Context).returns(T.nilable(CustomScalar)) }
def coerce_input(value, context)
return nil if value.nil?
CustomScalar.new
end
end
end

class CreateComment < GraphQL::Schema::Mutation
argument :required_scalar, NilableScalarType, required: true
argument :required_scalar_array, [NilableScalarType], required: true
argument :optional_scalar, NilableScalarType, required: false

def resolve(required_scalar:, required_scalar_array:, optional_scalar: nil)
# ...
end
end
RUBY

expected = <<~RBI
# typed: strong

class CreateComment
sig { params(required_scalar: ::CustomScalar, required_scalar_array: T::Array[::CustomScalar], optional_scalar: T.nilable(::CustomScalar)).returns(T.untyped) }
def resolve(required_scalar:, required_scalar_array:, optional_scalar: T.unsafe(nil)); end
end
RBI

assert_equal(expected, rbi_for(:CreateComment))
end

it "generates correct RBI for custom scalars with return types" do
add_ruby_file("create_comment.rb", <<~RUBY)
class CustomScalar; end
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