Make go build work as intended

[kolyshkin]

The aim of this commit is to make it so that

go get github.com/arduino/arduino-builder

will build a binary named arduino-builder and put it into
$GOPATH/bin so it will be instantly available (provided
the user have $GOPATH/bin in their $PATH).

This is as easy as

1. move all go files to /builder subdir
2. move the main.go to a top dir
3. fix the path to builder in main.go and tests

[v2: fix tests]
[v3: fix README and travis.yml]

[cmaglie]

You can already do the same with two arduino-builder in the path:

go build github.com/arduino/arduino-builder/arduino-builder

as explained in the readme: https://github.com/arduino/arduino-builder#building-from-source

[kolyshkin]

You can already do the same with two arduino-builder in the path:

go build github.com/arduino/arduino-builder/arduino-builder

as explained in the readme: https://github.com/arduino/arduino-builder#building-from-source

I followed these instructions before attempting this PR. The problems are:

1. arduino-builder is not installed into $GOPATH/bin (as it's expected in such cases)
2. A few commands are needed to make it work, while after this PR it's just one (as you can see in the patch, check the first change to README.md).

[kolyshkin]

@cmaglie in other words, the motivation for this PR is make it so that a single command is enoughto start using arduino-builder right away. Meaning, one can do this:

go get github.com/arduino/arduino-builder
arduino-builder # it works right away (provided $GOROOT/bin is in $PATH)

Currently, it's at least three (which is inconvenient and unexpected):

go get github.com/arduino/arduino-builder
go build github.com/arduino/arduino-builder/arduino-builder/...
cp $GOPATH/src/github.com/arduino/arduino-builder/arduino-builder/arduino-builder $GOPATH/bin # (or any other dir in $PATH)

[matthijskooijman]

IIUC, the problem with the current package is that main.go lives in a subpackage (or however it's called in go), and not in the main github.com/arduino/arduino-builder package? If so, wouldn't it work to do go get github.com/arduino/arduino-builder/arduino-builder? Or doesn't that pull in the dependencies from the main repo or something?

In any case, the changes proposed in this PR seem good to me, I've always thought this "duplicate" arduino-builder name is a bit weird.

Another thought: Instead of moving all the .go files from the root into a builder directory (where 147f3d9 moved them out of recently), why not just only move main.go into the root? Wouldn't that also work?

[kolyshkin]

wouldn't it work to do go get github.com/arduino/arduino-builder/arduino-builder?

In fact it works as intended! Not sure why I missed it when preparing this PR.

I'll close this one and prepare another -- for the sake of clarity.

Another thought: Instead of moving all the .go files from the root into a builder directory (where 147f3d9 > moved them out of recently), why not just only move main.go into the root? Wouldn't that also work?

Unfortunately not -- go does not allow one to mix two packages in the same dir:

kir@kd:~/go/src/github.com/arduino/arduino-builder$ mv arduino-builder/main.go .
kir@kd:~/go/src/github.com/arduino/arduino-builder$ go build .
can't load package: package github.com/arduino/arduino-builder: found packages builder (add_additional_entries_to_context.go) and main (main.go) in /home/kir/go/src/github.com/arduino/arduino-builder

Yet another workaround would be to move the cli utility (i.e. main.go) to a separate package. Say, rename this repo from arduino-builder to just builder and then create arduino-builder repo, moving the main.go to it. This way it will be less renames, but one more repository.