[Resolves #71] Add trimpath arg to gobuild

[stanleynguyen]

I'm not sure about -trimpath behavior with pre-1.13 go versions though.
I'm expecting -trimpath to not do anything for pre-1.13 versions

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[jonjohnsonjr]

I'm expecting -trimpath to not do anything for pre-1.13 versions

I think it actually complains if you pass a non-existent flag:

$ go build --foo bar
flag provided but not defined: -foo

You could use build constraints to only add -trimpath for go1.13 and above. This isn't perfect, though. Since we shell out to the go command, someone could have a go binary built with 1.13 but have go 1.12 installed, in which case that would fail. We could shell out to go version and do some string parsing, but I think that's actually worse.

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[stanleynguyen]

This makes me wonder if we should include some test cases to cover the actual execution of the ko binary as the current test cases failed to flag trimpath even when tested with go1.12 in Travis

[jonjohnsonjr]

This makes me wonder if we should include some test cases to cover the actual execution of the ko binary as the current test cases failed to flag trimpath even when tested with go1.12 in Travis

Yeah that would be hugely helpful. We could test ko ko publishing itself to a local docker daemon in travis, which would get you most of the coverage. We could even use something like kind or minikube to ko apply this test and assert that the output is what we expected.

[stanleynguyen]

@jonjohnsonjr I will include the test cases that covers what we've just discussed as well 👍

[stanleynguyen]

@jonjohnsonjr Added integration test using kind on travis env

[jonjohnsonjr]

Wow this is really awesome, thanks! Much better than I would have done myself 😄