support graceful migration for nullable enum types

[josharian]

Version

1.14.0

What happened?

#1485 improved handling of nullable fields with enum type. This is good.

But please consider adding a flag to opt out per-field. This is a backwards incompatible change; upgrading to the latest sqlc will cause code that used to compile not to compile any more. For a large code base, it would be much better to be able to upgrade field by field, rather than having to do one big bang. (There'd still be a big bang to the config file, but that's way safer and more manageable than a sprawling code change.)

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[kyleconroy]

I agree that changes like this aren't great. In this case, I felt it was necessary since these enums represented future errors. If you have a column with a nullable enum type, querying for that value would have always returned an error.

But please consider adding a flag to opt out per-field

While verbose, you can opt-out in certain cases using overrides. You should be able to specify the non-nullable enum type for the nullable value. Happy to provide a sample if necessary.