x/mobile: gobind fails on relatively simple example for iOS only

[steeve]

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

go version go1.8.3 darwin/amd64

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

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/steeve/go"
GORACE=""
GOROOT="/usr/local/Cellar/go/1.8.3/libexec"
GOTOOLDIR="/usr/local/Cellar/go/1.8.3/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/bs/51dlb_nn5k35xq9qfsxv9wc00000gn/T/go-build194780881=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

gomobile bind fails with the following code:

package mypkg

import "context"

type MyStruct struct {
}

func NewMyStruct(ctx context.Context) *MyStruct {
	return nil
}

What did you expect to see?

A successful bind.

What did you see instead?

When trying to build for iOS, this happens:

$ gomobile bind -v -target=ios github.com/steeve/mypkg
write /var/folders/bs/51dlb_nn5k35xq9qfsxv9wc00000gn/T/gomobile-work-008978683/src/gomobile_bind/interfaces.go
write /var/folders/bs/51dlb_nn5k35xq9qfsxv9wc00000gn/T/gomobile-work-008978683/gen/src/ObjC/interfaces.go
write /var/folders/bs/51dlb_nn5k35xq9qfsxv9wc00000gn/T/gomobile-work-008978683/src/gomobile_bind/interfaces.h
write /var/folders/bs/51dlb_nn5k35xq9qfsxv9wc00000gn/T/gomobile-work-008978683/src/gomobile_bind/interfaces.m
write /var/folders/bs/51dlb_nn5k35xq9qfsxv9wc00000gn/T/gomobile-work-008978683/fakegopath/pkg/darwin_arm/github.com/steeve/mypkg.a
write /var/folders/bs/51dlb_nn5k35xq9qfsxv9wc00000gn/T/gomobile-work-008978683/src/gomobile_bind/go_pouetmain.go
write /var/folders/bs/51dlb_nn5k35xq9qfsxv9wc00000gn/T/gomobile-work-008978683/src/gomobile_bind/go_main.go
write /var/folders/bs/51dlb_nn5k35xq9qfsxv9wc00000gn/T/gomobile-work-008978683/src/iosbin/main.go
write /var/folders/bs/51dlb_nn5k35xq9qfsxv9wc00000gn/T/gomobile-work-008978683/src/gomobile_bind/Mypkg.m
gomobile: type Context is in package context, which is not bound

This is due to the ctx parameter for the function.
It does build for Android, however.

[steeve]

So this is because of golang/mobile@e665403 and the fact that the method is named New*.
Renaming the method fixes the issue.

However, perhaps it should not fail and rather warn? Not sure about the behaviour.

[gopherbot]

Change https://golang.org/cl/101115 mentions this issue: bind: skip incompatible constructors in ObjC bindings