Updating playground should be as easy as `go generate`, without side-effects.

[dmitshur]

Right now, updating the playground requires running the update.sh script in its folder:

https://github.com/gopherjs/gopherjs.github.io/blob/master/playground/update.sh

However, it has a few limitations:

• It requires your GOROOT to be writeable (without sudo, or to run update.sh with sudo).
• It requires your GOPATH list to contain no more than 1 workspace.
• It requires rename command, which can be acquired with brew install rename but if possible, it'd be better not to require it. It can be replaced with a < 50 line Go program inside the repo, that way no external dependencies are needed.
• It has some non-zero side-effects, for example, it leaves the $GOPATH/bin/playground.js.map file behind and you have to clean it up manually afterwards.

It'd be great to make it so that updating the playground can be done by anyone who has gopherjs installed, even if their GOROOT is not writeable, and if their GOPATH contains multiple workspaces. It should also not have side-effects (having side-effects in a temporary folder is acceptable though).

Filing this to track the issue (I thought I already filed it earlier, but I guess I hadn't).