x/mobile: add support of Obj-C unsigned char

[tadovas]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version go1.9.2 darwin/amd64

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/tadovas/work/go/openvpnv3-go-bindings"
GORACE=""
GOROOT="/usr/local/Cellar/go/1.9.2/libexec"
GOTOOLDIR="/usr/local/Cellar/go/1.9.2/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/_j/73ymsvw56v989xyfwn6q18_m0000gn/T/go-build298437704=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"

What did you do?

import "Objc/NetworkExtension/NEPacket"
....
_ = NEPacket.NewWithData(data, uint8(PF_INET))

If possible, provide a recipe for reproducing the error.
A complete runnable program is good.
A link on play.golang.org is best.

What did you expect to see?

succesful gomobile bind command

What did you see instead?

gomobile: /Users/tadovas/work/go/openvpnv3-go-bindings/bin/gobind -lang=go,objc -outdir=/var/folders/_j/73ymsvw56v989xyfwn6q18_m0000gn/T/gomobile-work-389033767 -tags=ios ... failed: exit status 2
panic: invalid kind

goroutine 1 [running]:
golang.org/x/mobile/bind.(*ObjcWrapper).goType(0xc4200f79e0, 0xc420248d40, 0x0, 0x0, 0x0)
/Users/tadovas/work/go/openvpnv3-go-bindings/src/golang.org/x/mobile/bind/genobjcw.go:752 +0x290
golang.org/x/mobile/bind.(*ObjcWrapper).genFuncDecl(0xc4200f79e0, 0x132a000, 0xc42137f860)
/Users/tadovas/work/go/openvpnv3-go-bindings/src/golang.org/x/mobile/bind/genobjcw.go:600 +0xb5
golang.org/x/mobile/bind.(*ObjcWrapper).GenPackage(0xc4200f79e0, 0x3)
/Users/tadovas/work/go/openvpnv3-go-bindings/src/golang.org/x/mobile/bind/genobjcw.go:552 +0x62c
main.genObjcPackages(0x7ffeefbff93e, 0x48, 0xc42135d7e0, 0x3, 0x4, 0x0, 0x0, 0x0, 0x0, 0xc420047b08)
/Users/tadovas/work/go/openvpnv3-go-bindings/src/golang.org/x/mobile/cmd/gobind/gen.go:201 +0x4f9
main.run()
/Users/tadovas/work/go/openvpnv3-go-bindings/src/golang.org/x/mobile/cmd/gobind/main.go:128 +0xec1
main.main()
/Users/tadovas/work/go/openvpnv3-go-bindings/src/golang.org/x/mobile/cmd/gobind/main.go:45 +0x27

It seems that, gomobile correctly handles objc.Char types, but panics on objc.UChar type, which can be easily implemented. PR follows

[gopherbot]

Change https://golang.org/cl/135875 mentions this issue: bind: add support for objc.Uchar