datafusion-expr 54.0.0

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// distributed with this work for additional information
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// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

use arrow::datatypes::DataType;

use super::binary::{comparison_coercion, type_union_coercion};

/// Fold `coerce_fn` over `types`, starting from `initial_type`.
fn fold_coerce(
    initial_type: &DataType,
    types: &[DataType],
    coerce_fn: fn(&DataType, &DataType) -> Option<DataType>,
) -> Option<DataType> {
    types
        .iter()
        .try_fold(initial_type.clone(), |left_type, right_type| {
            coerce_fn(&left_type, right_type)
        })
}

/// Attempts to coerce the types of `list_types` to be comparable with the
/// `expr_type` for IN list predicates.
/// Returns the common data type for `expr_type` and `list_types`.
///
/// Uses comparison coercion because `x IN (a, b)` is semantically equivalent
/// to `x = a OR x = b`.
pub fn get_coerce_type_for_list(
    expr_type: &DataType,
    list_types: &[DataType],
) -> Option<DataType> {
    fold_coerce(expr_type, list_types, comparison_coercion)
}

/// Find a common coerceable type for `CASE expr WHEN val1 WHEN val2 ...`
/// conditions. Returns the common type for `case_type` and all `when_types`.
///
/// Uses comparison coercion because `CASE expr WHEN val` is semantically
/// equivalent to `expr = val`.
pub fn get_coerce_type_for_case_when(
    when_types: &[DataType],
    case_type: &DataType,
) -> Option<DataType> {
    fold_coerce(case_type, when_types, comparison_coercion)
}

/// Find a common coerceable type for CASE THEN/ELSE result expressions.
/// Returns the common data type for `then_types` and `else_type`.
///
/// Uses type union coercion because the result branches must be brought to a
/// common type (like UNION), not compared.
pub fn get_coerce_type_for_case_expression(
    then_types: &[DataType],
    else_type: Option<&DataType>,
) -> Option<DataType> {
    let (initial_type, remaining) = match else_type {
        None => then_types.split_first()?,
        Some(data_type) => (data_type, then_types),
    };
    fold_coerce(initial_type, remaining, type_union_coercion)
}