Sort fields and properties by MetadataToken.

[jhickson]

I found an issue that when writing parquet files using a writer like:

var writer =
    ParquetFie.CreateRowWriter<(long, int, double, int, long, short)>(
        "path/to/my.parquet",
        new [] {"C1", "C2", "C3", "C4", "C5", "C6"}
    );

the resulting parquet file would have column C1 typed as int and C2 as long - i.e. the first two column types were swapped.

Upon debugging it transpired that this was when Type.GetFields() was being used to build the write delegate. Type.GetFields() was not returning fields in declaration order so the mapping of column name to type failed. The .NET docs for this method (and Type.GetProperties()) explicitly state that order is not guaranteed. So, I have changed the code to sort by MemberInfo.MetadataToken as advised in this SO article.

Note that no unit tests have been added to cover this as it proved impossible to find a circumstance which reliably failed with the old code. It seems the order GetFields uses is usually declaration order but might change under certain runtime conditions. I have verified though that my change here fixed the issue I was seeing in my code.

[jhickson]

I'm not sure why the MacOS build is failing - I haven't touched the native code.

[GPSnoopy]

macOS failure is likely unrelated. Leave it with me.