Comment 1 by RMiB.email:

Sorry,
What is the expected output?
undefined C enum 'cairo_hint_style'

Comment 2:

Labels changed: added priority-go1, go1-must, removed priority-triage.

Status changed to Accepted.

Comment 3:

This appears to be an error due to invalid input: The enum is called _cairo_hint_style,
so it should be C.enum__cairo_hint_style:
package test
/*
typedef enum _cairo_hint_style {
    CAIRO_HINT_STYLE_DEFAULT,
    CAIRO_HINT_STYLE_NONE,
} cairo_hint_style_t;
int test(cairo_hint_style_t st) {
    return st;
}
*/
import "C" 
type CairoHintStyle int
func testfunc(st CairoHintStyle) {
    C.test(C.enum__cairo_hint_style(st))
}
No clear that we need to fix this for Go 1.
The crash is on line src/cmd/cgo/gcc.go:658 is due to r.Name.Type being nil.

Labels changed: added priority-triage, cgo, removed priority-go1, go1-must.

Comment 4:

Adjusting priority--crash on invalid input needs to be fixed, but not right away.

Labels changed: added priority-later, removed priority-triage.

Comment 5:

Update: the panic doesn't occur now, but apparently cgo still can't diagnose this
problem:
cgo.go:19[/tmp/.../_obj/cgo.cgo1.go:13]: cannot convert st (type CairoHintStyle) to type
[0]byte
cgo.go:19[/tmp/.../_obj/cgo.cgo1.go:13]: cannot use ([0]byte)(st) (type [0]byte) as type
_Ctype_cairo_hint_style_t in function argument
a corrected version could be:
package main
/*
typedef enum _cairo_hint_style {
    CAIRO_HINT_STYLE_DEFAULT,
    CAIRO_HINT_STYLE_NONE,
} cairo_hint_style_t;
int test(cairo_hint_style_t st) {
    return st;
}
*/
import "C"
type CairoHintStyle int
func f(st CairoHintStyle) {
    C.test(C.cairo_hint_style_t(st))
}

Comment 6:

Labels changed: added go1.1.

Comment 8:

Labels changed: added size-m.

Comment 9:

Labels changed: added go1.1maybe, removed go1.1.

Comment 10:

Labels changed: added go1.2maybe, removed go1.1maybe.

Comment 11:

Labels changed: added go1.3maybe, removed go1.2maybe.

Comment 12:

Labels changed: removed go1.3maybe.

Comment 13:

Labels changed: added go1.3maybe.

Comment 14:

Labels changed: added release-none, removed go1.3maybe.

Comment 15:

Labels changed: added repo-main.

Comment 16:

go build now reports
# _/home/iant/tmp
./test.go:19:12: unexpected: -1-byte enum type - enum cairo_hint_style {}
Marking this as fixed.

Status changed to Fixed.

When you compile the example from the first post (go version devel +5dbe071 Sat Jun 6 02:17:49 2015 +0000 linux/amd64
):

# test1
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x0 pc=0x40ec96]

goroutine 1 [running]:
main.(*Package).rewriteRef(0xc20808e2a0, 0xc2080a0000)
        /opt/go.1.5/src/cmd/cgo/gcc.go:610 +0x1466
main.(*Package).Translate(0xc20808e2a0, 0xc2080a0000)
        /opt/go.1.5/src/cmd/cgo/gcc.go:170 +0x197
main.main()
        /opt/go.1.5/src/cmd/cgo/main.go:269 +0x1059

other code that reproduces the error:

package main

/**/
import "C" 

func main() {
    var a = C.enum_test(1)
}