InvalidProgramException on prerelease when first field is a non-numeric type

[jnm2]

@mgravell It seems very likely that this one is on me via #1242. I'll get a full repro and fix it ASAP.

https://www.myget.org/feed/stackoverflow/package/nuget/Dapper/1.60.14 works fine with (int, string, string, DateTime?, DateTime?, DateTime?, decimal?, DateTime?, string, int?, DateTime?, DateTime?, int?) rows.

With (string, byte[], byte[]), it breaks:

System.InvalidProgramException:
Common Language Runtime detected an invalid program.
at Deserialize669fc2c6-0ab9-4b1c-ae66-ee2bfbcc0010(IDataReader )
at Dapper.SqlMapper.d__34`1.MoveNext() in C:\projects\dapper\Dapper\SqlMapper.Async.cs:line 500

[jnm2]

ValueTuple<byte[]> and ValueTuple<string> both repro this, so I'm likely treating a reference type like a value type somewhere.

Oddly, the existing (int, string) tests don't trigger this bug. It appears to affect the first but not the second tuple element.

[jnm2]

Think I spotted it. In the main path, local 0 holds the current reader field index for retrieval on exceptions for diagnostic purposes. In the ValueTuple path, this local does not exist, so the following code writes into whatever local was created, which may be a string or byte[] local, created later on in the IL generation:

https://github.com/StackExchange/Dapper/blob/fcd8a70279fbe19e2aa0dbc81f7625a0ddae5e2f/Dapper/SqlMapper.cs#L3411-L3417

[jnm2]

That was it. PR incoming.