feat(extensions): add subscript_operator and index_of functions

extensions/functions_list.yaml

@@ -130,3 +130,32 @@ scalar_functions:
             value: func<any1 -> boolean?>
         nullability: DECLARED_OUTPUT
         return: boolean?
+
+  - name: "subscript_operator"
+    description: >-
+      Returns the element at the specified index from the list, corresponding
+      to the common array subscript operator [].
+
+      Index is 1-based (i.e., the first element is at index 1). Out-of-bounds
+      access (index <= 0 or index > list length) returns null.
+    impls:
+      - args:
+          - name: input
+            value: list<any1>
+          - name: index
+            value: i64
+        nullability: DECLARED_OUTPUT
+        return: any1?
+
+  - name: "index_of"
+    description: >-
+      Returns the 1-based index of the first occurrence of the specified value
+      in the list, or null if the value is not found.
+    impls:
+      - args:
+          - name: input
+            value: list<any1>
+          - name: value
+            value: any1
+        nullability: DECLARED_OUTPUT
+        return: i64?

tests/cases/list/index_of.test

@@ -0,0 +1,27 @@
+### SUBSTRAIT_SCALAR_TEST: v1.0
+### SUBSTRAIT_INCLUDE: '/extensions/functions_list.yaml'
+
+# basic: Find element in list (1-based index)
+index_of([10, 20, 30]::list<i32>, 10::i32) = 1::i64?
+index_of([10, 20, 30]::list<i32>, 20::i32) = 2::i64?
+index_of([10, 20, 30]::list<i32>, 30::i32) = 3::i64?
+index_of(['a', 'b', 'c']::list<string>, 'b'::string) = 2::i64?
+
+# not_found: Element not in list returns null
+index_of([10, 20, 30]::list<i32>, 5::i32) = null::i64?
+index_of([10, 20, 30]::list<i32>, 100::i32) = null::i64?
+
+# first_match: Returns index of first occurrence
+index_of([10, 20, 20, 30]::list<i32>, 20::i32) = 2::i64?
+
+# empty_list: Empty list returns null
+index_of([]::list<i32>, 1::i32) = null::i64?
+
+# null_list: Null list returns null
+index_of(null::list?<i32>, 1::i32) = null::i64?
+
+# null_value: Searching for null returns null
+index_of([10, 20, 30]::list<i32>, null::i32?) = null::i64?
+
+# find_null_element: Finding null in list with nulls
+index_of([1, null, 3]::list<i32?>, null::i32?) = 2::i64?

tests/cases/list/subscript_operator.test

@@ -0,0 +1,31 @@
+### SUBSTRAIT_SCALAR_TEST: v1.0
+### SUBSTRAIT_INCLUDE: '/extensions/functions_list.yaml'
+
+# basic: Basic positive index (1-based)
+subscript_operator([10, 20, 30]::list<i32>, 1::i64) = 10::i32?
+subscript_operator([10, 20, 30]::list<i32>, 2::i64) = 20::i32?
+subscript_operator([10, 20, 30]::list<i32>, 3::i64) = 30::i32?
+subscript_operator(['a', 'b', 'c']::list<string>, 2::i64) = 'b'::string?
+
+# out_of_bounds_positive: Positive index exceeds list length
+subscript_operator([10, 20, 30]::list<i32>, 5::i64) = null::i32?
+subscript_operator([10, 20, 30]::list<i32>, 100::i64) = null::i32?
+
+# zero_out_of_bounds: Zero index is out of bounds
+subscript_operator([10, 20, 30]::list<i32>, 0::i64) = null::i32?
+
+# negative_out_of_bounds: Negative indices are out of bounds
+subscript_operator([10, 20, 30]::list<i32>, -1::i64) = null::i32?
+subscript_operator([10, 20, 30]::list<i32>, -3::i64) = null::i32?
+
+# null_list: Null list returns null
+subscript_operator(null::list?<i32>, 1::i64) = null::i32?
+
+# null_index: Null index returns null
+subscript_operator([10, 20, 30]::list<i32>, null::i64?) = null::i32?
+
+# null_element: Retrieving a null element returns null
+subscript_operator([1, null, 3]::list<i32?>, 2::i64) = null::i32?
+
+# empty_list: Out of bounds on empty list
+subscript_operator([]::list<i32>, 1::i64) = null::i32?