`go build` rebuilds unnecessarily

Question

go build and go run are very slow on a tiny program I have (cgo invocations in particular). I\'d like go to cache the binary so that it only rebuilds when the source is new

Answer 1

I wrote a tool that happens to solve this as a side effect. go build alone will not check if the executable it's producing is already up to date. go install does, and if you tweak it to install to a location of your choice, then you'll get the desired result, similar to go build.

You can see the behaviour you describe by doing something like this:

$ go get -d github.com/anacrolix/missinggo/cmd/nop
$ time go run "$GOPATH"/src/github.com/anacrolix/missinggo/cmd/nop/*.go

real    0m0.176s
user    0m0.142s
sys     0m0.048s

That's on a warm run. go run will link on every invocation, just as go build would. Note that github.com/anacrolix/missinggo/cmd/nop is an program that does absolutely nothing.

Here's invoking the same package, using my tool, godo:

$ time godo github.com/anacrolix/missinggo/cmd/nop

real    0m0.073s
user    0m0.029s
sys     0m0.033s

For larger programs, the difference should be more pronounced.

So in summary, your standard tooling option is to use go install, or an alternative like godo.