gorm.Errors, which usefully implements `error` for an `[]error` as
returned by `DB.GetError()` was already exported, but because it used a
private field `errors`, it was not able to be created due to the
compile-time error:
implicit assignment of unexported field 'errors' in gorm.Errors literal
The trivial solution would be to export the `errors` field on
`gorm.Errors`, but this led to the issue that the common pattern of
checking `err != nil` failed because a struct{error: nil} != nil.
We can take advantage of type aliasing here to make Errors an []error,
which can in fact be nil and would pass `err != nil` on the happy path.
* Remove `(Errors) GetErrors()`, as it's less useful when Errors is an
[]error which can be iterated over. While this is technically a
breaking change, we never expose an Errors and its difficult to build
one (it can be done with the existing `(Errors) Add(error)`), but
awkwardly. This removal can be reverted without issue and we can make
it an identity method, but it seemed an opportune time to reduce API
surface area on something that likely isn't used.
* Remove errorsInterface, as it's not useful without `(Errors)
GetErrors()`
* Change `(*Errors) Add(error)` => `(Errors) Add(error...) Errors`
because we can't modify even a *Errors when it's a type alias. This is
more idiomatic as it follows the pattern of `slice = append(slice,
element)` Go developers are familiar with.
Caleb Thompson