How to build/install cross-compiled nested packages quickly? - go

Question

I have a repository with a group of nested go packages organized as follows:
$GOPATH/src/
- mypackage/common/utils.go
- mypackage/app1/main.go
- mypackage/app2/main.go
...
It compiles to a handful of binaries. For releasing, I'm cross-compiling for a multitude of platforms/archs (I deploy repeatedly with a different GOOS and GOARCH). I'm trying to write the compilation results to a directory of my choice, but I'm fighting with the toolchain.
I can:
Combine GOBIN and go install when compiling for my own architecture
(i.e. not cross compiling):
# build + output all binaries in /somedir/bin
# this works great when compiling for my local architecture.
GOBIN=/somedir/bin go install mypackage/app1 mypackage/app2 mypackage/app3
But unfortunately, GOBIN conflicts with cross-compilation e.g:
# Throws: "cannot install cross-compiled binaries when GOBIN is set"
GOBIN=/somedir/bin GOARCH=amdm64 GOOS=darwin go install mypackage/app1 mypackage/app2
Use go build with GOOS=X and GOARCH=Y for each subpackage
# cross compile one of the binaries
cd /output/darwin-386-bin/ && \
GOOS=darwin GOARCH=386 go build mypackage/app1
# but if given multiple binaries, there is no output. (as documented)
GOOS=darwin GOARCH=386 go build mypackage/app1 mypackage/app2
When go build is given multiple packages, it no longer emits binaries -- it just checks that the code compiles. To emit all the binaries, it seems I have to run go build once for each subpackage, so it takes longer, esp when building with -a.
Another possible issue with using go build like this, is that it's potentially mixing binaries and intermediary results across multiple architectures in the same workspace. But maybe that's just a matter of taste. Hopefully the toolchain keeps cached results separate for different architectures.
How is this handled in practice? Should I treat each subpackage as an individual package, despite their shared common code (would it then be safe to build them all in parallel)?
Related articles:
go build vs go install: https://groups.google.com/forum/#!topic/golang-nuts/s8Csz3-7EXA (Little info on cross-compilation, or multipackage setups)
cross compile with go 1.5.: https://dave.cheney.net/2015/08/22/cross-compilation-with-go-1-5 (does not specifically address multipackage / common code compilation. Also, the statement about having to recompile the standard library into /usr/local/go/pkg seems to no longer hold in 1.9.1, as far as I can tell)
Go build multiple nested packages: Go build multiple/nested packages? . ( The accepted answer, go build ./... behaves the same as passing multiple packages in a single build command, and therefore outputs no binaries. The thread also does not cover cross compilation)

Answer 1

What I'm about to suggest feels like a hack at best, but it might work for you if you're cross-compiling stuff in a container or an isolated build environment.
You can drop the GOBIN from the install command:
# I'm not on this platform, so this is a cross compile
GOOS=darwin GOARCH=amd64 go install mypackage/app1 mypackage/app2
Assuming your package is in $GOPATH/src/mypackage the above command will install the two binaries to:
$GOPATH/bin/darwin_amd64/{app1, app2}
and the .a compile dependency files in:
$GOPATH/pkg/darwin_amd64/mypackage/{app1,app2,common}
If you're running this in a for loop for all the platforms you plan on supporting, one nuisance with this process is that when you pass GOOS=x GOARCH=y matching your local architecture (i.e. not cross compiling), then the executables will be placed directly in $GOPATH/bin/ and not $GOPATH/bin/x_y/.
(packages on the other hand always end up in $GOPATH/pkg/x_y/, cross compilation or not).
To determine your local architecture, you can follow steps in this answer: https://stackoverflow.com/a/35669816/5556676 .
Simulating GOBIN=/foo/bin GOOS=x GOARCH=y go install mypackage/app{1,2,3}
Changing $GOPATH has little effect on where go install writes output. With some go commands, like go get, you tweak where packages are installed by adding a new component at the front of $GOPATH. But in go 1.9, go install will always copy binaries in the bin/ folder that's a sibling of the src/ which contains the packages to install.
Instead of using GOBIN=/foo/bin, you can pretend your source files are in /foo/src/mypackage (you may use a symlink), and then do GOPATH=/foo GOOS=x GOARCH=y go install mypackage/app{1,2,3}. This will put binaries in /foo/bin, because of the behavior I describe in the previous paragraph.
It's probably simpler to just grab the binaries from where you expect them to be though, than mucking with copying source trees around.