Index the partitionValues map with column's physical name

[nicklan]

From the protocol:

In name mode, readers must resolve columns in the data files by their physical names as given by the column metadata property delta.columnMapping.physicalName in the Delta schema. Partition values and column level statistics will also be resolved by their physical names. For columns that are not found in the files, nulls need to be returned. Column ids are not used in this mode for resolution purposes.

So we need to map to physical name otherwise we won't find the column. Note the same is true for id mode, so this won't break when we add support for that.

[scovich]

Change looks good in isolation. My only question/concern would be -- how many other places are we using logical names where we should be using mapped physical names instead? Do we have a way to find them and prevent future mix-ups?

[nicklan]

how many other places are we using logical names where we should be using mapped physical names instead? Do we have a way to find them and prevent future mix-ups?

A good question. I did a grep through the code for field.name and didn't see anything else concerning. I will think if there's anything more systematic we could do. (something like using fields everywhere so that the method that wants the name could call the correct name vs logical_name could work, but would complicate other things, so not sure if it's worth it)