Re: [PR] feat: support `FixedSizeList` Type Coercion [arrow-datafusion]

[via GitHub]

Weijun-H commented on code in PR #9108:
URL: https://github.com/apache/arrow-datafusion/pull/9108#discussion_r1493916770


##########
datafusion/expr/src/signature.rs:
##########
@@ -123,29 +128,171 @@ pub enum TypeSignature {
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub enum ArrayFunctionSignature {
     /// Specialized Signature for ArrayAppend and similar functions
-    /// The first argument should be List/LargeList, and the second argument 
should be non-list or list.
+    /// If `allow_null` is true, the function also accepts a single argument 
of type Null.
+    /// The first argument should be List/LargeList/FixedSizedList, and the 
second argument should be non-list or list.
     /// The second argument's list dimension should be one dimension less than 
the first argument's list dimension.
     /// List dimension of the List/LargeList is equivalent to the number of 
List.
     /// List dimension of the non-list is 0.
-    ArrayAndElement,
+    ArrayAndElement(bool),
     /// Specialized Signature for ArrayPrepend and similar functions
+    /// If `allow_null` is true, the function also accepts a single argument 
of type Null.
     /// The first argument should be non-list or list, and the second argument 
should be List/LargeList.
     /// The first argument's list dimension should be one dimension less than 
the second argument's list dimension.
-    ElementAndArray,
-    ArrayAndIndex,
+    ElementAndArray(bool),
+    /// Specialized Signature for ArrayEqual and similar functions
+    /// If `allow_null` is true, the function also accepts a single argument 
of type Null.
+    /// The first argument should be List/LargeList/FixedSizedList, and the 
second argument should be Int64.
+    ArrayAndIndex(bool),
+    /// Specialized Signature for ArrayEmpty and similar functions
+    /// The function takes a single argument that must be a 
List/LargeList/FixedSizeList
+    /// or something that can be coerced to one of those types.
+    /// If `allow_null` is true, the function also accepts a single argument 
of type Null.
+    Array(bool),
+}
+
+impl ArrayFunctionSignature {
+    /// Arguments to ArrayFunctionSignature
+    /// `current_types` - The data types of the arguments
+    /// `allow_null_coercion` - Whether null type coercion is allowed
+    /// Returns the valid types for the function signature
+    pub fn get_type_signature(
+        &self,
+        current_types: &[DataType],
+    ) -> Result<Vec<Vec<DataType>>> {
+        fn array_append_or_prepend_valid_types(
+            current_types: &[DataType],
+            is_append: bool,
+            allow_null_coercion: bool,
+        ) -> Result<Vec<Vec<DataType>>> {
+            if current_types.len() != 2 {
+                return Ok(vec![vec![]]);
+            }
+
+            let (array_type, elem_type) = if is_append {
+                (&current_types[0], &current_types[1])
+            } else {
+                (&current_types[1], &current_types[0])
+            };
+
+            // We follow Postgres on `array_append(Null, T)`, which is not 
valid.
+            if array_type.eq(&DataType::Null) && !allow_null_coercion {

Review Comment:
   `array_has` , `array_positions`, `array_remove` and `array_remove_all`should 
use it.
   ```
   D SELECT list_contains(null, 1);
   ┌────────────────────────┐
   │ list_contains(NULL, 1) │
   │         int32          │
   ├────────────────────────┤
   │                        │
   └────────────────────────┘
   
   D SELECT list_position(null, 1);
   ┌────────────────────────┐
   │ list_position(NULL, 1) │
   │         int32          │
   ├────────────────────────┤
   │                        │
   └────────────────────────┘
   
   ```
   
   ```
   **Schema (PostgreSQL v15)**
   
   ---
   
   **Query #1**
   
       SELECT array_remove(NULL, 2);
   
   | array_remove |
   | ------------ |
   |              |
   
   ```



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