foo.go:4:8: error: initialization expressions for ‘b’ and ‘c’ depend upon each other
     a, b = f()
        ^
foo.go:5:5: note: ‘c’ defined here
     c    = b
     ^
foo.go:5:5: error: initialization expressions for ‘c’ and ‘b’ depend upon each other
foo.go:4:8: note: ‘b’ defined here
     a, b = f()
        ^
/home/iant/foo4.go:5:5: error: initialization expression for ‘c’ depends upon itself
     c    = b
     ^

foo.go:4:8: initialization cycle for b
foo.go:4:8:     b refers to
foo.go:8:6:     f refers to
foo.go:5:5:     c refers to
foo.go:4:8:     b

package main

var (
    b, a = f()
    c    = b
)

func f() (int, int) {
    return c, c
}

func main() {}

a, b = f()
a
f()
f // mark f as done, but still traverse it
c
b
f()
// f has been marked done, so it is not checked and the cycle is undetected

b, a = f()
f()
f
c
b // cycle detected