Review use of panics in datafusion-row crate

[andygrove]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/accessor.rs":234             _ => unreachable!(),
"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/jit/reader.rs":139                 _ => unimplemented!(),
"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/jit/reader.rs":158                 _ => unimplemented!(),
"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/jit/writer.rs":207         _ => unimplemented!(),
"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/layout.rs":160         _ => unreachable!(),
"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/reader.rs":71         $NATIVE::from_le_bytes($SELF.data[start..end].try_into().unwrap())
"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/reader.rs":84                 $NATIVE::from_le_bytes(self.data[start..end].try_into().unwrap())
"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/reader.rs":302                     .unwrap();
"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/reader.rs":310                     .unwrap();
"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/reader.rs":337     let to = to.as_any_mut().downcast_mut::<BinaryBuilder>().unwrap();
"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/reader.rs":350     let to = to.as_any_mut().downcast_mut::<BinaryBuilder>().unwrap();
"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/reader.rs":377         _ => unimplemented!(),
"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/reader.rs":404         _ => unimplemented!(),
"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/writer.rs":304                     .unwrap();
"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/writer.rs":329     let from = from.as_any().downcast_ref::<Date32Array>().unwrap();
"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/writer.rs":339     let from = from.as_any().downcast_ref::<Date64Array>().unwrap();
"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/writer.rs":349     let from = from.as_any().downcast_ref::<StringArray>().unwrap();
"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/writer.rs":364     let from = from.as_any().downcast_ref::<BinaryArray>().unwrap();
"/home/andy/git/apache/arrow-datafusion/datafusion/row/src/writer.rs":397         _ => unimplemented!(),

Describe the solution you'd like
Review code that can panic and see where it makes sense to return a Result instead. For example, It is generally better to use ? than unwrapon results.

The goal is not to remove all panics but review and make sure we are using them appropriately. Bonus points for adding documentation for invariants.

Describe alternatives you've considered
None

Additional context
Generated by https://github.com/andygrove/no-need-to-panic

[askoa]

Can I take a stab at this? Also, is the error type DataFusionError::Internal okay to return instead of panic?

[qrilka]

In #3354 (comment) it's said that

panic seems acceptable approach for read_field* functions.

If that's valid then is this ticket still needed? BTW no-need-to-panic seems to be gone...

[alamb]

Indeed in fact I think datafusion-row was removed a while ago, so this ticket is no longer relevant. Thanks @qrilka