Allow overriding repr for custom types

[oprypin]

In Bazel's Starlark, the following holds:

• str(Label('//:hi')) == '//:hi'
• repr(Label('//:hi')) == 'Label("//:hi")'

However in starlark-go it is impossible to implement a Label object that would behave like this, instead the value of repr is forced to be '"//:hi"' per the straightforward implementation:

starlark-go/starlark/library.go

Line 958 in e6e8e7c

func repr(thread *Thread, _ *Builtin, args Tuple, kwargs []Tuple) (Value, error) {

Are there any plans to allow overriding repr of a particular type to be able to achieve this distinction?

[adonovan]

Are there any plans to allow overriding repr of a particular type to be able to achieve this distinction?

No, there are no plans. If this feature is really important it could be supported by defining a Reprable interface that the repr function would probe for, but our experience building a Bazel-like tool using starlark-go was that this wasn't necessary, even though it was technically a point of difference between the Go API and the java.starlark.net API.