This test verifies that we produce diagnostics related to mismatching
unexported interface methods in non-workspace packages.

Previously, we would fail to produce a diagnostic because we trimmed the AST.
See golang/go#56943.
-- main.go --
package main

import (
	"go/ast"
	"go/token"
)

func main() {
	var a int               //@diag(re"(a) int", re"a declared.*not used")
	var _ ast.Expr = node{} //@diag("node{}", re"missing.*exprNode")
}

type node struct{}

func (node) Pos() token.Pos { return 0 }
func (node) End() token.Pos { return 0 }