One of the things that the Go project talked about in Eleven Years of Go, posted in November, is the plans for Go 1.16 and Go 1.17, and along with them the plans for Go modules. A short summary of all of that information is that Go modules are soon going to be our only option. This is said straight up in the article:
We will also finally wind down support for GOPATH-based development: any programs using dependencies other than the standard library will need a
The current specifics are set out in the GOPATH wiki page. Go 1.16, expected in
February 2021, will change the default to
go.mod even if you are under $GOPATH/src). Go 1.17 will
entirely remove support for anything other than Go module mode.
Given how the Go authors usually work, I expect this to remove the
actual code that supports 'GOPATH development mode', not just remove
access to it (for instance by removing checking $GO111MODULE and
hard-wiring the value).
(It's possible that this timeline will turn out to be too aggressive and the Go authors will get enough pushback to postpone the removal past Go 1.17. The upgrade to Go 1.16 will be when people who are currently quietly working in GOPATH development mode will be forced to confront this, so this may uncover more people with more practical problems than expected.)
Given this aggressive timeline, I don't think there's any point in
explicitly setting $GO111MODULE to 'auto' or 'off' (contrary to
what I thought a year or so ago, which I
admit that I didn't follow). If anything, you should set
now to buy yourself a bit of extra time to find any problems and
figure out workarounds and new ways of working if you need them.
I'm not going to go that far, but I'm lazy.
I have mixed feelings about the shift overall. I think Go modules
are clearly better for development (including for enabling easy
self-contained source code), but as someone
who mostly consumes Go programs that I get with '
go get ...',
it's probably going to make my life more complicated.
(I'd say that it'll make it harder for me to keep up with what
programs have updated source code (cf),
but in practice I no longer even look; I just do '
go get -u' on
everything every so often.)