support Is comparison on MySQLError

[chriskirkland]

Description

Adds support for comparison of MySQLError instances with errors.Is. This useful for comparing errors (either client-side or server-side) in application code, particularly for things like circuit breakers and retriers.

Checklist

• Code compiles correctly
• Created tests which fail without the change (if possible)
• All tests passing
• Extended the README / documentation, if necessary
• Added myself / the copyright holder to the AUTHORS file

[shogo82148]

It sounds good.
Please fix the tests with Go 1.12 by adding // +build go113.

We can drop support Go 1.12 because the latest version of Go is 1.16.
But this change may be not an enough reason to do it.

[methane]

We can drop support Go 1.12 because the latest version of Go is 1.16.
But this change may be not an enough reason to do it.

I think we should drop old versions support now, because we just released v1.6.

[shogo82148]

I dropped support of Go 1.12. #1211

[chriskirkland]

@methane @shogo82148 looks like the PR checks are failing because of a decrease in coverage because of newly "uncovered" lines in rows.go which this PR doesn't touch. Any suggestions how I can work around that?

[julienschmidt]

Thanks!