proposal: x/tools/packages: Use type aliases in packages.Package's Types tree.

[dils2k]

Proposal Details

I have a package that contains a type alias and a method, that has a parameter, type of which is the type alias.

package foo

type Alias = string

func Foo(s Alias) {}

When I parse the package using tools/packages, the type alias in the parameter is ignored and string type is set.

pkg, _ := packages.Load(&packages.Config{
	Dir:  "./foo",
	Mode: packages.NeedName | packages.NeedSyntax | packages.NeedTypes,
})

fn := pkg[0].Types.Scope().Lookup("Foo").(*types.Func)
sig := fn.Type().(*types.Signature)
typ := sig.Params().At(0).Type()

fmt.Println(typ.String()) // --> string, but actual type is Alias

This issue proposes to use actual type aliases in Types tree of *package.Package.

[dils2k]

MB it's a bug btw, not sure

[timothy-king]

This is the expected behavior for Go versions <= 1.22. Alias is just another name for string. For a long time there was no representation of Alias as a go/types.Type. This is expected to change starting in go1.23 #63223 (also behind a GODEBUG flag).

Support for this is expected to start in go/types in go1.23. The status for support from x/tools/go/packages for go1.23 is still in progress: #63223 (comment). IIUC the way I expect this will be available to packages users will be to compile with >= go1.23.

No proposal is needed for this. Closing.