cmd/go/internal/modload: fix sort condition in (*replacementRepo).Versions

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>

1 files changed, 3 insertions, 3 deletions

diff --git a/src/cmd/go/internal/modload/query.go b/src/cmd/go/internal/modload/query.go
index d16a247f72..3b27e66d01 100644
--- a/src/cmd/go/internal/modload/query.go
+++ b/src/cmd/go/internal/modload/query.go
@@ -891,12 +891,12 @@ func (rr *replacementRepo) ModulePath() string { return rr.repo.ModulePath() }
 // Versions returns the versions from rr.repo augmented with any matching
 // replacement versions.
 func (rr *replacementRepo) Versions(prefix string) ([]string, error) {
-	versions, err := rr.repo.Versions(prefix)
+	repoVersions, err := rr.repo.Versions(prefix)
 	if err != nil && !errors.Is(err, os.ErrNotExist) {
 		return nil, err
 	}
 
-	added := false
+	versions := repoVersions
 	if index != nil && len(index.replace) > 0 {
 		path := rr.ModulePath()
 		for m, _ := range index.replace {
@@ -906,7 +906,7 @@ func (rr *replacementRepo) Versions(prefix string) ([]string, error) {
 		}
 	}
 
-	if !added {
+	if len(versions) == len(repoVersions) { // No replacement versions added.
 		return versions, nil
 	}