[]struct{} leads to incorrectly generated code

[echlebek]

The attached example leads to code that does not build. (Go 1.9 on my machine, but almost certainly on all release versions of Go.)

package ffjsonbug

type Foo struct {
        Bar []struct{}
}

Here is the relevant section of generated code:

        if j.Bar != nil {
            buf.WriteString(`[`)
            for i, v := range j.Bar {
                if i != 0 {
                    buf.WriteString(`,`)
                }
                /* Inline struct. type=struct {} kind=struct */
                buf.WriteString(`{}`)
            }
            buf.WriteString(`]`)
        } else {
            buf.WriteString(`null`)
        }

The special case for struct{} causes v to be un-used.