skip[fuzz]: fix random_list gen (#7875)

This fixes the random_list generator used in Arbitrary. We should likely
rewrite all of this to be easier to use.

Signed-off-by: Joe Isaacs <joe.isaacs@live.co.uk>

Author: joseph-isaacs

vortex-array/src/arrays/arbitrary.rs

@@ -235,29 +235,43 @@ fn random_list(
     null: Nullability,
     chunk_len: Option<usize>,
 ) -> Result<ArrayRef> {
+    let array_length = chunk_len.unwrap_or(u.int_in_range(0..=20)?);
+    // Worst-case total elements: each list can have up to 20 elements.
+    let max_total_elements = array_length as u64 * 20;
+
     match u.int_in_range(0..=5)? {
-        0 => random_list_with_offset_type::<i16>(u, elem_dtype, null, chunk_len),
-        1 => random_list_with_offset_type::<i32>(u, elem_dtype, null, chunk_len),
-        2 => random_list_with_offset_type::<i64>(u, elem_dtype, null, chunk_len),
-        3 => random_list_with_offset_type::<u16>(u, elem_dtype, null, chunk_len),
-        4 => random_list_with_offset_type::<u32>(u, elem_dtype, null, chunk_len),
-        5 => random_list_with_offset_type::<u64>(u, elem_dtype, null, chunk_len),
-        _ => unreachable!("int_in_range returns a value in the above range"),
+        0 if i16::max_value_as_u64() >= max_total_elements => {
+            random_list_with_offset_type::<i16>(u, elem_dtype, null, array_length)
+        }
+        1 if i32::max_value_as_u64() >= max_total_elements => {
+            random_list_with_offset_type::<i32>(u, elem_dtype, null, array_length)
+        }
+        3 if u16::max_value_as_u64() >= max_total_elements => {
+            random_list_with_offset_type::<u16>(u, elem_dtype, null, array_length)
+        }
+        4 if u32::max_value_as_u64() >= max_total_elements => {
+            random_list_with_offset_type::<u32>(u, elem_dtype, null, array_length)
+        }
+        // i64 and u64 always fit; also the fallback for when narrower types don't.
+        _ => {
+            if u.arbitrary::<bool>()? {
+                random_list_with_offset_type::<i64>(u, elem_dtype, null, array_length)
+            } else {
+                random_list_with_offset_type::<u64>(u, elem_dtype, null, array_length)
+            }
+        }
     }
 }
 
 /// Creates a random list array with the given [`IntegerPType`] for the internal offsets child.
-///
-/// If the `chunk_len` is specified, the length of the array will be equal to the chunk length.
 fn random_list_with_offset_type<O: IntegerPType>(
     u: &mut Unstructured,
     elem_dtype: &Arc<DType>,
     null: Nullability,
-    chunk_len: Option<usize>,
+    array_length: usize,
 ) -> Result<ArrayRef> {
-    let array_length = chunk_len.unwrap_or(u.int_in_range(0..=20)?);
-
-    let mut builder = ListViewBuilder::<O, O>::with_capacity(Arc::clone(elem_dtype), null, 20, 10);
+    let mut builder =
+        ListViewBuilder::<O, O>::with_capacity(Arc::clone(elem_dtype), null, array_length, 10);
 
     for _ in 0..array_length {
         if null == Nullability::Nullable && u.arbitrary::<bool>()? {