cgo blows up with runtime error: `cgo argument has Go pointer to Go pointer`

[paultag]

panic: runtime error: cgo argument has Go pointer to Go pointer

goroutine 1 [running, locked to thread]:
panic(0x65d200, 0xc4200185f0)
    /usr/lib/go-1.7/src/runtime/panic.go:500 +0x1a1
github.com/sourcegraph/go-webkit2/webkit2.(*WebView).RunJavaScript(0xc420018530, 0xc4200595d8, 0xf, 0xc4200185e0)
    /home/paultag/.goenvs/epson/src/github.com/sourcegraph/go-webkit2/webkit2/webview.go:147 +0xea
main.main.func3(0xc4200380b8, 0x3)
    /home/paultag/dev/local/go-webkit2/cmd/webkit-eval-js/evaljs.go:84 +0xfb
reflect.Value.call(0x650f40, 0xc42000c5a0, 0x13, 0x6aeb1c, 0x4, 0xc42000c7b0, 0x2, 0x2, 0x0, 0x6490c0, ...)
    /usr/lib/go-1.7/src/reflect/value.go:434 +0x5c8
reflect.Value.Call(0x650f40, 0xc42000c5a0, 0x13, 0xc42000c7b0, 0x2, 0x2, 0xc4200185d0, 0x82, 0x0)
    /usr/lib/go-1.7/src/reflect/value.go:302 +0xa4
github.com/gotk3/gotk3/glib.goMarshal(0x16b2180, 0x0, 0x2, 0x7ffe3a989690, 0x7ffe3a989610, 0x0)
    /home/paultag/.goenvs/epson/src/github.com/gotk3/gotk3/glib/glib.go:283 +0x601
github.com/gotk3/gotk3/glib._cgoexpwrap_cca433d51eec_goMarshal(0x16b2180, 0x0, 0x2, 0x7ffe3a989690, 0x7ffe3a989610, 0x0)
    ??:0 +0x5b
github.com/gotk3/gotk3/gtk._Cfunc_gtk_main()
    ??:0 +0x41
github.com/gotk3/gotk3/gtk.Main()
    /home/paultag/.goenvs/epson/src/github.com/gotk3/gotk3/gtk/gtk.go:766 +0x14
main.main()
    /home/paultag/dev/local/go-webkit2/cmd/webkit-eval-js/evaljs.go:93 +0x474

https://groups.google.com/forum/#!searchin/golang-nuts/cgo$20argument$20has$20Go$20pointer$20to$20Go$20pointer/golang-nuts/gnH0nhPf36I/4Shly3gxEwAJ

https://github.com/golang/go/issues/12416

[paultag]

Design docs: https://github.com/golang/proposal/blob/master/design/12416-cgo-pointers.md

[paultag]

Ah, this is likely a gotk bug, I'll pass that along.

[paultag]

Nevermind this is go-webkit2 bug. Sorry for the noise.

[paultag]

One possible fix may be to do:

index 3f79cc0..638db8b 100644
--- a/webkit2/gasyncreadycallback.go
+++ b/webkit2/gasyncreadycallback.go
@@ -25,6 +25,8 @@ func newGAsyncReadyCallback(f interface{}) (cCallback C.GAsyncReadyCallback, use
        if rf.Kind() != reflect.Func {
                return nil, nil, errors.New("f is not a function")
        }
-       cbinfo := &garCallback{rf}
+       data := C.malloc(C.size_t(unsafe.Sizeof(garCallback{})))
+       cbinfo := (*garCallback)(data)
+       cbinfo.f = rf
        return C.GAsyncReadyCallback(C._gasyncreadycallback_call), C.gpointer(unsafe.Pointer(cbinfo)), nil
 }

diff --git a/webkit2/webview.go b/webkit2/webview.go
index 8249757..5da804a 100644
--- a/webkit2/webview.go
+++ b/webkit2/webview.go
@@ -125,6 +125,7 @@ func (v *WebView) RunJavaScript(script string, resultCallback func(result *gojs.
        var err error
        if resultCallback != nil {
                callback := func(result *C.GAsyncResult) {
+                       C.free(unsafe.Pointer(userData))
                        var jserr *C.GError
                        jsResult := C.webkit_web_view_run_javascript_finish(v.webView, result, &jserr)
                        if jsResult == nil {

(And so forth)

[paultag]

Closed in #35