minor: enforce lint rule clippy::needless_pass_by_value to datafusion-functions

[Standing-Man]

Which issue does this PR close?

• Closes Enforce lint rule clippy::needless_pass_by_value to datafusion-functions #18758.

Rationale for this change

• enforce lint rule clippy::needless_pass_by_value to datafusion-functions.

What changes are included in this PR?

Are these changes tested?

Are there any user-facing changes?

[Jefffrey]

This change seems odd; input_value should already be a reference I believe?

[Standing-Man]

No, StringArrType is just a trait. input_value isn’t automatically a reference—we need to explicitly borrow it when required.

[Jefffrey]

But if we look at StringArrayType it is implemented for references:

https://docs.rs/arrow/latest/arrow/array/trait.StringArrayType.html

[Standing-Man]

You mean to keep the function definition like this:

pub fn digest_utf8_array_impl<'a, StringArrType>(
    self, 
    input_value: StringArrType,
) -> ArrayRef 
where
    StringArrType: StringArrayType<'a>,
{ ... }

and then call it like this:

self.digest_utf8_array_impl::<&GenericStringArray<T>>(&v)

…but the Rust compiler still complains and doesn’t accept it.

[Jefffrey]

My point is this might be a false positive by clippy because if we look here for example:

datafusion/datafusion/functions/src/crypto/basic.rs

Lines 260 to 263 in f1ecacc

	DataType::Binary | DataType::LargeBinary => {
	let v = value.as_binary::<T>();
	self.digest_binary_array_impl::<&GenericBinaryArray<T>>(v)
	}

v is already of type &GenericBinaryArray<T>; it is already a reference 🤔

[Standing-Man]

Yes, but Clippy warns that input_value is not consumed in the function body, suggesting we take a reference instead. Therefore, the parameter of digest_utf8_array_impl needs to be a double reference (&&).

[Jefffrey]

I guess we'll just go along with this; for reference: #18839 (comment)

[Jefffrey]

But if we look at StringArrayType it is implemented for references:

https://docs.rs/arrow/latest/arrow/array/trait.StringArrayType.html

[Standing-Man]

Thanks @Jefffrey for taking the time to review this PR!