[GitHub] [arrow] jorgecarleitao edited a comment on pull request #8829: ARROW-10804: Removed undefined behavior from parquet crate, causing tests to fail

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jorgecarleitao edited a comment on pull request #8829:
URL: https://github.com/apache/arrow/pull/8829#issuecomment-743720998


   @nevi-me , I would really appreciate your help here: there are major problems emerging in the parquet crate when I try to remove an unsafe struct.
   
   The background of this change is that `FatPtr` is using `Buffer::capacity` and `Buffer::raw_data()` which is brittle and difficult to reason because a pointer is only valid within a container's `len`, not `capacity`. This is also causing the error that rust compiler safeguard us against when borrowing a mutable and immutable reference at the same time.
   
   This is blocking #8796 
   
   I verified that in all 4 tests the content passed to `ColumnReaderImpl::read_batch` is the same in master and after this PR, but for some reason the outcome of that call is different, which hints that there is some other invariant beyond the ones that we are telling the compiler about through the typing and lifetime system.


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