peter-toth commented on PR #58501:
URL: https://github.com/apache/spark/pull/58501#issuecomment-5573245594

   Thank you for the review. Both taken.
   
   1. The section headings were gone from the description, and I found the 
cause: a `git rebase --continue` through an editor uses the `default` commit 
cleanup mode, which strips lines beginning with `#`, so the `###` headings were 
silently dropped from the commit message I built the description from. 
Restored, and the description is the five template sections again.
   
   2. You are right, and my sentence was wrong rather than imprecise. 
`StructField.metadata` is erased too, since the erasure rebuilds each field as 
`StructField(i.toString, ...)`. It is deliberate, but "the naming and nothing 
more" did not say so. The description now says what goes: the struct field 
names, every nullability, and a field's metadata, which travels with its name. 
Metadata goes because nothing that compares or hashes a row reads it, and 
because `DataType.equalsStructurally` ignores it too, so keeping it would make 
the erasure answer differently from the predicate it stands for.
   
   The code already said this at `erasePositionalNames`, and one of the 22 
oracle pairs covers it, so only the description was out of step.
   


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