Test that direct reference to embedded fields in struct literals produces diagnostics before Go 1.27.
Ref: go.dev/issues/78553

-- flags --
-max_go_command=go1.26

-- go.mod --
module mod.com

go 1.22

-- main.go --
package main

type E1 struct {
	A int
}

type T struct {
	E1
}

func main() {
	_ = T{
		A: 1, //@diag(re"A", re"unknown field")
	}
}
