add try_new_with_length constructor to FixedSizeList

Also fixes existing tests and adds some more test cases for degenerate
`FixedSizeList`s.

Signed-off-by: Connor Tsui <connor.tsui20@gmail.com>

Author: connortsui20

arrow-array/src/array/fixed_size_list_array.rs

@@ -125,7 +125,15 @@ pub struct FixedSizeListArray {
 }
 
 impl FixedSizeListArray {
-    /// Create a new [`FixedSizeListArray`] with `size` element size, panicking on failure
+    /// Create a new [`FixedSizeListArray`] with `size` element size, panicking on failure.
+    ///
+    /// Note that if `size == 0` and `nulls` is `None` (a degenerate, non-nullable
+    /// `FixedSizeListArray`), this function will set the length of the array to 0.
+    ///
+    /// If you would like to have a degenerate, non-nullable `FixedSizeListArray` with arbitrary
+    /// length, use the [`try_new_with_length()`] constructor.
+    ///
+    /// [`try_new_with_length()`]: Self::try_new_with_length
     ///
     /// # Panics
     ///
@@ -134,12 +142,20 @@ impl FixedSizeListArray {
         Self::try_new(field, size, values, nulls).unwrap()
     }
 
-    /// Create a new [`FixedSizeListArray`] from the provided parts, returning an error on failure
+    /// Create a new [`FixedSizeListArray`] from the provided parts, returning an error on failure.
+    ///
+    /// Note that if `size == 0` and `nulls` is `None` (a degenerate, non-nullable
+    /// `FixedSizeListArray`), this function will set the length of the array to 0.
+    ///
+    /// If you would like to have a degenerate, non-nullable `FixedSizeListArray` with arbitrary
+    /// length, use the [`try_new_with_length()`] constructor.
+    ///
+    /// [`try_new_with_length()`]: Self::try_new_with_length
     ///
     /// # Errors
     ///
     /// * `size < 0`
-    /// * `values.len() / size != nulls.len()`
+    /// * `values.len() != nulls.len() * size` if `nulls` is `Some`
     /// * `values.data_type() != field.data_type()`
     /// * `!field.is_nullable() && !nulls.expand(size).contains(values.logical_nulls())`
     pub fn try_new(
@@ -152,23 +168,81 @@ impl FixedSizeListArray {
             ArrowError::InvalidArgumentError(format!("Size cannot be negative, got {size}"))
         })?;
 
-        let len = match s {
-            0 => nulls.as_ref().map(|x| x.len()).unwrap_or_default(),
-            _ => {
-                let len = values.len() / s.max(1);
-                if let Some(n) = nulls.as_ref() {
-                    if n.len() != len {
-                        return Err(ArrowError::InvalidArgumentError(format!(
-                            "Incorrect length of null buffer for FixedSizeListArray, expected {} got {}",
-                            len,
-                            n.len(),
-                        )));
-                    }
+        let len = if s == 0 {
+            // Note that for degenerate and non-nullable `FixedSizeList`s, we will set the length to
+            // 0 (`_or_default`).
+            nulls.as_ref().map(|x| x.len()).unwrap_or_default()
+        } else {
+            // Note that `s` might not divide `values.len()`, so we need to check this
+            let len = values.len() / s;
+
+            // Check that the null buffer length is correct (if it exists).
+            if let Some(null_buffer) = &nulls {
+                if s * null_buffer.len() != values.len() {
+                    return Err(ArrowError::InvalidArgumentError(format!(
+                        "Incorrect length of values buffer for FixedSizeListArray, expected {} got {}",
+                        s * null_buffer.len(),
+                        values.len(),
+                    )));
                 }
-                len
             }
+
+            len
         };
 
+        Self::try_new_with_length(field, size, values, nulls, len)
+    }
+
+    /// Create a new [`FixedSizeListArray`] from the provided parts, returning an error on failure.
+    ///
+    /// This method exists to allow the construction of arbitrary length degenerate (`size == 0`)
+    /// and non-nullable `FixedSizeListArray`s. If you want a nullable `FixedSizeListArray`, then
+    /// you can use [`try_new()`] instead.
+    ///
+    /// [`try_new()`]: Self::try_new
+    ///
+    /// # Errors
+    ///
+    /// * `size < 0`
+    /// * `nulls.len() != len` if `nulls` is `Some`
+    /// * `values.len() != len * size`
+    /// * `values.data_type() != field.data_type()`
+    /// * `!field.is_nullable() && !nulls.expand(size).contains(values.logical_nulls())`
+    pub fn try_new_with_length(
+        field: FieldRef,
+        size: i32,
+        values: ArrayRef,
+        nulls: Option<NullBuffer>,
+        len: usize,
+    ) -> Result<Self, ArrowError> {
+        let s = size.to_usize().ok_or_else(|| {
+            ArrowError::InvalidArgumentError(format!("Size cannot be negative, got {size}"))
+        })?;
+
+        if let Some(null_buffer) = &nulls
+            && null_buffer.len() != len
+        {
+            return Err(ArrowError::InvalidArgumentError(format!(
+                "Invalid null buffer for FixedSizeListArray, expected {len} found {}",
+                null_buffer.len()
+            )));
+        }
+
+        if s == 0 && !values.is_empty() {
+            return Err(ArrowError::InvalidArgumentError(format!(
+                "An degenerate FixedSizeListArray should have no underlying values, found {} values",
+                values.len()
+            )));
+        }
+
+        if values.len() != len * s {
+            return Err(ArrowError::InvalidArgumentError(format!(
+                "Incorrect length of values buffer for FixedSizeListArray, expected {} got {}",
+                len * s,
+                values.len(),
+            )));
+        }
+
         if field.data_type() != values.data_type() {
             return Err(ArrowError::InvalidArgumentError(format!(
                 "FixedSizeListArray expected data type {} got {} for {:?}",
@@ -673,23 +747,28 @@ mod tests {
         let list = FixedSizeListArray::new(field.clone(), 2, values.clone(), Some(nulls));
         assert_eq!(list.len(), 3);
 
-        let list = FixedSizeListArray::new(field.clone(), 4, values.clone(), None);
-        assert_eq!(list.len(), 1);
+        let list = FixedSizeListArray::new(field.clone(), 3, values.clone(), None);
+        assert_eq!(list.len(), 2);
+
+        let err =
+            FixedSizeListArray::try_new_with_length(field.clone(), 1, values.clone(), None, 4)
+                .unwrap_err();
+        assert_eq!(
+            err.to_string(),
+            "Invalid argument error: Incorrect length of values buffer for FixedSizeListArray, expected 4 got 6"
+        );
 
         let err = FixedSizeListArray::try_new(field.clone(), -1, values.clone(), None).unwrap_err();
         assert_eq!(
             err.to_string(),
             "Invalid argument error: Size cannot be negative, got -1"
         );
 
-        let list = FixedSizeListArray::new(field.clone(), 0, values.clone(), None);
-        assert_eq!(list.len(), 0);
-
         let nulls = NullBuffer::new_null(2);
         let err = FixedSizeListArray::try_new(field, 2, values.clone(), Some(nulls)).unwrap_err();
         assert_eq!(
             err.to_string(),
-            "Invalid argument error: Incorrect length of null buffer for FixedSizeListArray, expected 3 got 2"
+            "Invalid argument error: Incorrect length of values buffer for FixedSizeListArray, expected 4 got 6"
         );
 
         let field = Arc::new(Field::new_list_field(DataType::Int32, false));
@@ -712,11 +791,35 @@ mod tests {
     }
 
     #[test]
-    fn empty_fixed_size_list() {
+    fn degenerate_fixed_size_list() {
         let field = Arc::new(Field::new_list_field(DataType::Int32, true));
         let nulls = NullBuffer::new_null(2);
         let values = new_empty_array(&DataType::Int32);
-        let list = FixedSizeListArray::new(field.clone(), 0, values, Some(nulls));
+        let list = FixedSizeListArray::new(field.clone(), 0, values.clone(), Some(nulls.clone()));
         assert_eq!(list.len(), 2);
+
+        // Test invalid null buffer length.
+        let err = FixedSizeListArray::try_new_with_length(
+            field.clone(),
+            0,
+            values.clone(),
+            Some(nulls),
+            5,
+        )
+        .unwrap_err();
+        assert_eq!(
+            err.to_string(),
+            "Invalid argument error: Invalid null buffer for FixedSizeListArray, expected 5 found 2"
+        );
+
+        // Test non-empty values for degenerate list.
+        let non_empty_values = Arc::new(Int32Array::from(vec![1, 2, 3]));
+        let err =
+            FixedSizeListArray::try_new_with_length(field.clone(), 0, non_empty_values, None, 3)
+                .unwrap_err();
+        assert_eq!(
+            err.to_string(),
+            "Invalid argument error: An degenerate FixedSizeListArray should have no underlying values, found 3 values"
+        );
     }
 }