'go mod tidy' has been able to use replaced versions since CL 152739,
but 'go get' failed for many of the same paths. Now that we are
recommending 'go get' more aggressively due to #40728, we should make
that work too.

In the future, we might consider factoring out the new replacementRepo
type so that 'go list' can report the new versions as well.

For #41577
For #41416
For #37438
Updates #26241

Change-Id: I9140c556424b584fdd9bdd0a747842774664a7d8
Reviewed-on: https://go-review.googlesource.com/c/go/+/258220
Trust: Bryan C. Mills <bcmills@google.com>
Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

…sions

In CL 258220 I added replacement versions to the repo versions used in
the modload.Query functions. The versions are computed from a map in
the modfile index, which has a nondeterministic iteration order.

I added a short-circuit condition to skip sorting in the (vastly
common) case where no replacement versions are added. However, while
cleaning up the change I accidentally deleted the line of code that
sets that condition. As a result, the test of that functionality
(mod_get_replaced) has been failing nondeterministically.

This change fixes the condition by comparing the slices before and
after adding versions, rather than by setting a separate variable.
The test now passes reliably (tested with -count=200).

Updates #41577
Updates #41416
Updates #37438
Updates #26241

Change-Id: I49a66a3a5510da00ef42b47f20a168de66100db6
Reviewed-on: https://go-review.googlesource.com/c/go/+/263266
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>