Previously, gopls would fall back on a gopath resolver when running
goimports from a directory containing go.work (but not go.mod). Fix this
by update the code to recognize that GOWORK also puts goimports into
module mode.
All the work to _support_ go.work had already been done, but the tests
were only passing because they were setting GO111MODULE=on explicitly
(and therefore GOMOD=/dev/null was satisfying the pre-existing check).
Also add a test for the regression in gopls.
Fixesgolang/go#52784
Change-Id: I31df6f71a949a5668e8dc001b3ee25ad26f2f927
Reviewed-on: https://go-review.googlesource.com/c/tools/+/413689
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>