[GitHub] [arrow-datafusion] HaoYang670 opened a new issue, #4165: The functions in `type_coercion` should return `Result`, not `Option`

[GitBox <gi...@apache.org>]

HaoYang670 opened a new issue, #4165:
URL: https://github.com/apache/arrow-datafusion/issues/4165

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   (This section helps Arrow developers understand the context and *why* for this feature, in addition to  the *what*)
   Currently, in the `type_coercion` mod, we have some pub functions returning `Result`, such as 
   ```rust
   pub fn coerce_types(
       lhs_type: &DataType,
       op: &Operator,
       rhs_type: &DataType,
   ) -> Result<DataType> {
   ```
   , and others returning `Option`:
   ```rust
   pub fn comparison_coercion(lhs_type: &DataType, rhs_type: &DataType) -> Option<DataType> {
   ```
   
   We should let all of them to return `Result` so that we can find the error as early as possible. Currently, we do the conversion from `None` to `Error` in the downstream code:
   ```rust
                   let case_when_coerce_type =
                       get_coerce_type_for_case_when(&then_types, &else_type);
                   match case_when_coerce_type {
                       None => Err(DataFusionError::Internal(format!(
                           "Failed to coerce then ({:?}) and else ({:?}) to common types in CASE WHEN expression",
                           then_types, else_type
                       ))),
   ```
   , which should be avoided.
   
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   **Describe alternatives you've considered**
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   **Additional context**
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