It appears that both cmd/compile and go/types already accept code like this:

package main

func main() {
    (*struct{ error }).Error(nil)
}

Perhaps we just need to relax the spec.

This requires more subtle changes in the spec than anticipated - simply removing the grammar in https://golang.org/ref/spec#Method_expressions and replacing MethodExpression with Type in Operand may do it, but then warrant more simplifications (regarding composite literals). Too subtle to squeeze in before 1.7. Still, would be nice to fix since cmd/compile and go/types seem to accept it effortlessly, and it's a clean generalization.

But esoteric and of no real use for now, so no urgency. Postponing again.

It's worth noting that because of type aliases, the formerly syntactically invalid code:

interface{f()}.f(nil)

can now equivalently be written as the syntactically valid:

type u = interface{f()}
u.f(nil)

gccgo rejects the former, but accepts the latter. cmd/compile and go/types accept both.

Notably though, when interface{f()}.f is replaced with (*struct{error}).Error, gccgo still rejects both forms. (cmd/compile and go/types still accept both.)

Removing Go2 label. go/types and cmd/compile accept these forms (and have been accepting them for some time), so at this point this is really just about updating the spec to match the compilers. For the same reasons it's also not a language change.

Change https://golang.org/cl/73233 mentions this issue: spec: match syntax for method expressions with implementations

Change https://golang.org/cl/73554 mentions this issue: test: add test cases for method expressions with literal receiver types

@griesemer I don't know if/how it's related, but when I try the code from #9060 (comment), having the note

It appears that both cmd/compile and go/types already accept code like this:

in the playground I get

go.(*struct { error }).Error: call to external function
main.main: relocation target go.(*struct { error }).Error not defined
main.main: undefined: "go.(*struct { error }).Error"

Tried also locally with go version go1.9.1 linux/amd64 and the result is the same.

@griesemer Update: Nevermind, I found you've already reported this in #22444.

Change https://golang.org/cl/81775 mentions this issue: test: disable broken test for 1.10