make the env.sh script idempotent

[nebkor]

Hello! I noticed that the dev env setup script would keep pre-pending the omicron paths to $PATH; this just removes the duplicates (bonus of removing all dupes from your $PATH) while preserving order; works with zsh and bash.

Before, after sourcing the env script twice:

$ echo $PATH |tr ':' '\n'
/home/ardent/git/omicron/out/mgd/root/opt/oxide/mgd/bin
/home/ardent/git/omicron/out/dendrite-stub/bin
/home/ardent/git/omicron/out/clickhouse
/home/ardent/git/omicron/out/cockroachdb/bin
/home/ardent/git/omicron/out/mgd/root/opt/oxide/mgd/bin
/home/ardent/git/omicron/out/dendrite-stub/bin
/home/ardent/git/omicron/out/clickhouse
/home/ardent/git/omicron/out/cockroachdb/bin
/home/ardent/bin
....

After:

$ source env.sh ; source env.sh
......
$ echo $PATH |tr ':' '\n'
/home/ardent/git/omicron/out/mgd/root/opt/oxide/mgd/bin
/home/ardent/git/omicron/out/dendrite-stub/bin
/home/ardent/git/omicron/out/clickhouse
/home/ardent/git/omicron/out/cockroachdb/bin
/home/ardent/bin
....

[davepacheco]

Thanks for putting this together. While I can see the appeal of making this avoid adding to PATH every time you run it, I don't really like this change. That seemed to be the consensus when I asked around internally, too, so I'm going to close this (though if others at Oxide want to push for a change here, please go ahead and make it).

To give a little more detail, these are the kinds of things that make me nervous about a change like this: the impact of getting it wrong is pretty high (mucking with people's paths can lead to very confusing bugs and even security issues); this one-liner is not super self-evident and bash isn't a great environment for automated testing; this sort of problem has lots of edge cases (e.g., paths with spaces, or multiple paths that differ only by case); and this one-liner relies on several different commands existing and accepting the same flags and producing the same output on all the systems we care about.

[nebkor]

No worries; thanks for taking a look!