x/tools/gopls: feature request: refactor.extract.struct

[danp]

in slack

Suppose I have:

type X struct {
  A, B, C, D string
}

and I want to move to:

type Y struct {
  A, B string
}

type X struct {
  Y
  C, D string
}

It would be nice to have some help with that.

[findleyr]

Thanks, this is a neat idea, and feels like a natural extraction operation to offer.

Thinking about what could be broken by this refactoring:

• unkeyed literals
• type conversions
• certain rare assignments (var x X = struct{A, B, C, D string}{})

Given that any dependency on field layout is discouraged outside the local package, it probably suffices to check for these constraints only in the package(s) defining the type. Note that we don't have to worry about type conversions where the underlying is forwarded (type X2 X).

(Did I miss anything?)

[tttoad]

@findleyr
Initialization outside of local packages should be refactored.

a := pkg.X{A: "s", B: "s", C: "s", D: "s"} => a := pkg.X{Y: pkg.Y{A: "s", B: "s"}, C: "s", D: "s"}

[adonovan]

If any field is embedded, the method sets may change.