func applyBug() {
    src := `                                                                                                                                                                                                                                  
package p                                                                                                                                                                                                                                     
import foo "bar"                                                                                                                                                                                                                              
func f(x foo.t) {}                                                                                                                                                                                                                            
`
    fset := token.NewFileSet()
    file, err := parser.ParseFile(fset, "", src, 0)
    if err != nil {
        panic(err)
    }
    pre := func(c *astutil.Cursor) bool {
        if sel, ok := c.Node().(*ast.SelectorExpr); ok {
            if id, ok := sel.X.(*ast.Ident); ok && id.Obj == nil && id.Name == "foo" {
                c.Replace(&ast.Ident{Name: "foo_t"})
            }
        }
        return true
    }
    astutil.Apply(file, pre, nil)
    var buf bytes.Buffer
    if err := format.Node(&buf, fset, file); err != nil {
        panic(err)
    }
    fmt.Println(buf.String())
}

package p

import foo "bar"

func f(x foo_t,) {}