x/mobile: No way to identify when being built for iossimulator

[rob-deutsch]

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

$ go version
go version go1.19.5 darwin/amd64

Does this issue reproduce with the latest release?

Yes. This is the latest release

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/rob/Library/Caches/go-build"
GOENV="/Users/rob/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/rob/go/pkg/mod"
GONOPROXY="github.com/rob-deutsch"
GONOSUMDB="github.com/rob-deutsch"
GOOS="darwin"
GOPATH="/Users/rob/go"
GOPRIVATE="github.com/rob-deutsch"
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/Cellar/go/1.19.5/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.19.5/libexec/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.19.5"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/dev/null"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/_s/36069dcj0c9dffd1lsrg4l_h0000gn/T/go-build106360914=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

1. Created a library that relies on statically linked libraries (included as .syso)
2. Make sure that there are different .syso files for the iOS sdk and the iPhoneSimulator sdk
3. Ran gomobile bind -target ios/arm64,iossimulator/arm64 -o Library.xcframework

What did you see?

Received this error message:

gomobile: xcodebuild -create-xcframework -framework /var/folders/_s/36069dcj0c9dffd1lsrg4l_h0000gn/T/gomobile-work-4172868616/iossimulator/iphonesimulator/Library.framework -framework /var/folders/_s/36069dcj0c9dffd1lsrg4l_h0000gn/T/gomobile-work-4172868616/ios/iphoneos/Library.framework -output Library.xcframework failed: exit status 70
error: binaries with multiple platforms are not supported '/var/folders/_s/36069dcj0c9dffd1lsrg4l_h0000gn/T/gomobile-work-4172868616/iossimulator/iphonesimulator/Library.framework/Library'

This issue is caused by the fact that go is trying to link the ios static libraries instead of the iossimulator static library.

What did you expect to see?

There needs to be a way to use build tags to identify whether we're building for ios/arm64 or iossimulator/arm64. That way different static libraries can be linked depending on e.g.:

//go:build arm64 && ios && !iossimulator

and

//go:build arm64 && ios && iossimulator

[changkun]

If I recall correctly, iossimulator is not a build tag but a build target of the gomobile command.

[rob-deutsch]

That's correct, but it should also be a build tag, because the compiler might need to know when gomobile is building the iossimulator build target.

My Go build needs to do different things depending on whether its being built for ios or iossimulator.