Limit visibility of internal impl functions in function crates (#18877)

## Which issue does this PR close?

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N/A

## Rationale for this change

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Whilst reviewing some recent PRs (#18839 & #18768) I noticed we have
quite a few inner implementation functions that are public for some
reason, which give the false impression these are meant to be public
APIs (and thus any changes to their signature needs to be restricted).
Went through and limited the functions to private where possible to try
reduce our public API footprint.

## What changes are included in this PR?

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PR.
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Change inner functions in functions & nested-functions crates to be
private, away from public.

- There are still some that are left public such as some regex ones,
because they are used directly in benches

## Are these changes tested?

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Compiler itself.

## Are there any user-facing changes?

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Yes, quite a few functions are now private, but I don't think they were
meant to be public in the first place.

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change` label.
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Author: Jefffrey

datafusion/functions-nested/src/cardinality.rs

@@ -117,8 +117,7 @@ impl ScalarUDFImpl for Cardinality {
     }
 }
 
-/// Cardinality SQL function
-pub fn cardinality_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn cardinality_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array] = take_function_args("cardinality", args)?;
     match array.data_type() {
         Null => Ok(Arc::new(UInt64Array::from_value(0, array.len()))),

datafusion/functions-nested/src/concat.rs

@@ -352,8 +352,7 @@ impl ScalarUDFImpl for ArrayConcat {
     }
 }
 
-/// Array_concat/Array_cat SQL function
-pub(crate) fn array_concat_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_concat_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     if args.is_empty() {
         return exec_err!("array_concat expects at least one argument");
     }
@@ -453,8 +452,7 @@ fn concat_internal<O: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
 
 // Kernel functions
 
-/// Array_append SQL function
-pub(crate) fn array_append_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_append_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array, values] = take_function_args("array_append", args)?;
     match array.data_type() {
         DataType::Null => make_array_inner(&[Arc::clone(values)]),
@@ -464,8 +462,7 @@ pub(crate) fn array_append_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     }
 }
 
-/// Array_prepend SQL function
-pub(crate) fn array_prepend_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_prepend_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [values, array] = take_function_args("array_prepend", args)?;
     match array.data_type() {
         DataType::Null => make_array_inner(&[Arc::clone(values)]),

datafusion/functions-nested/src/dimension.rs

@@ -189,8 +189,7 @@ impl ScalarUDFImpl for ArrayNdims {
     }
 }
 
-/// Array_dims SQL function
-pub fn array_dims_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_dims_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array] = take_function_args("array_dims", args)?;
     let data: Vec<_> = match array.data_type() {
         List(_) => as_list_array(&array)?
@@ -214,8 +213,7 @@ pub fn array_dims_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     Ok(Arc::new(result))
 }
 
-/// Array_ndims SQL function
-pub fn array_ndims_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_ndims_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array] = take_function_args("array_ndims", args)?;
 
     fn general_list_ndims(array: &ArrayRef) -> Result<ArrayRef> {

datafusion/functions-nested/src/distance.rs

@@ -141,7 +141,7 @@ impl ScalarUDFImpl for ArrayDistance {
     }
 }
 
-pub fn array_distance_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_distance_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array1, array2] = take_function_args("array_distance", args)?;
     match (array1.data_type(), array2.data_type()) {
         (List(_), List(_)) => general_array_distance::<i32>(args),

datafusion/functions-nested/src/empty.rs

@@ -110,8 +110,7 @@ impl ScalarUDFImpl for ArrayEmpty {
     }
 }
 
-/// Array_empty SQL function
-pub fn array_empty_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_empty_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array] = take_function_args("array_empty", args)?;
     match array.data_type() {
         List(_) => general_array_empty::<i32>(array),

datafusion/functions-nested/src/except.rs

@@ -126,8 +126,7 @@ impl ScalarUDFImpl for ArrayExcept {
     }
 }
 
-/// Array_except SQL function
-pub fn array_except_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_except_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array1, array2] = take_function_args("array_except", args)?;
 
     match (array1.data_type(), array2.data_type()) {

datafusion/functions-nested/src/flatten.rs

@@ -130,8 +130,7 @@ impl ScalarUDFImpl for Flatten {
     }
 }
 
-/// Flatten SQL function
-pub fn flatten_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn flatten_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array] = take_function_args("flatten", args)?;
 
     match array.data_type() {

datafusion/functions-nested/src/length.rs

@@ -150,8 +150,7 @@ macro_rules! array_length_impl {
     }};
 }
 
-/// Array_length SQL function
-pub fn array_length_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_length_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     if args.len() != 1 && args.len() != 2 {
         return exec_err!("array_length expects one or two arguments");
     }

datafusion/functions-nested/src/min_max.rs

@@ -113,14 +113,7 @@ impl ScalarUDFImpl for ArrayMax {
     }
 }
 
-/// array_max SQL function
-///
-/// There is one argument for array_max as the array.
-/// `array_max(array)`
-///
-/// For example:
-/// > array_max(\[1, 3, 2]) -> 3
-pub fn array_max_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_max_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array] = take_function_args("array_max", args)?;
     match array.data_type() {
         List(_) => array_min_max_helper(as_list_array(array)?, max_batch),
@@ -202,7 +195,7 @@ impl ScalarUDFImpl for ArrayMin {
     }
 }
 
-pub fn array_min_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_min_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array] = take_function_args("array_min", args)?;
     match array.data_type() {
         List(_) => array_min_max_helper(as_list_array(array)?, min_batch),

datafusion/functions-nested/src/position.rs

@@ -141,8 +141,7 @@ impl ScalarUDFImpl for ArrayPosition {
     }
 }
 
-/// Array_position SQL function
-pub fn array_position_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_position_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     if args.len() < 2 || args.len() > 3 {
         return exec_err!("array_position expects two or three arguments");
     }
@@ -152,6 +151,7 @@ pub fn array_position_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
         array_type => exec_err!("array_position does not support type '{array_type}'."),
     }
 }
+
 fn general_position_dispatch<O: OffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
     let list_array = as_generic_list_array::<O>(&args[0])?;
     let element_array = &args[1];
@@ -292,8 +292,7 @@ impl ScalarUDFImpl for ArrayPositions {
     }
 }
 
-/// Array_positions SQL function
-pub fn array_positions_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
+fn array_positions_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
     let [array, element] = take_function_args("array_positions", args)?;
 
     match &array.data_type() {