Trim unnecessary dependencies for ordered generic constraint. (#4709)

A generic test function was introduced in #4515 using
`constraints.Ordered` from golang.org/x/exp/constaints. This
unfortunately introduces further transitive dependencies on packages
such as golang.org/x/tools which has versions with various breaking
changes. This makes it more difficult to pull in nats-server in
downstream projects.

By inlining the trivial `ordered` definition, we can trim this
dependency.

An alternative to this change would be to downgrade the required version
of golang.org/x/exp since the constraints package has been there (and
unchanged) since 2022-02-02.

Signed-off-by: Augusto Roman <[email protected]>

go.mod

@@ -11,7 +11,6 @@ require (
  github.com/nats-io/nuid v1.0.1
  go.uber.org/automaxprocs v1.5.3
  golang.org/x/crypto v0.14.0
- golang.org/x/exp v0.0.0-20230905200255-921286631fa9
  golang.org/x/sys v0.13.0
  golang.org/x/time v0.3.0
 )

go.sum

@@ -18,8 +18,6 @@ go.uber.org/automaxprocs v1.5.3 h1:kWazyxZUrS3Gs4qUpbwo5kEIMGe/DAvi5Z4tl2NW4j8=
 go.uber.org/automaxprocs v1.5.3/go.mod h1:eRbA25aqJrxAbsLO0xy5jVwPt7FQnRgjW+efnwa1WM0=
 golang.org/x/crypto v0.14.0 h1:wBqGXzWJW6m1XrIKlAH0Hs1JJ7+9KBwnIO8v66Q9cHc=
 golang.org/x/crypto v0.14.0/go.mod h1:MVFd36DqK4CsrnJYDkBA3VC4m2GkXAM0PvzMCn4JQf4=
-golang.org/x/exp v0.0.0-20230905200255-921286631fa9 h1:GoHiUyI/Tp2nVkLI2mCxVkOjsbSXD66ic0XW0js0R9g=
-golang.org/x/exp v0.0.0-20230905200255-921286631fa9/go.mod h1:S2oDrQGGwySpoQPVqRShND87VCbxmc6bL1Yd2oYrm6k=
 golang.org/x/sys v0.0.0-20190130150945-aca44879d564/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.13.0 h1:Af8nKPmuFypiUBjVoU9V20FiaFXOcuZI21p0ycVYYGE=
 golang.org/x/sys v0.13.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=

server/test_test.go

@@ -21,8 +21,6 @@ import (
  "strings"
  "testing"
  "time"
-
- "golang.org/x/exp/constraints"
 )
 
 // DefaultTestOptions are default options for the unit tests.
@@ -135,7 +133,7 @@ func require_Len(t *testing.T, a, b int) {
  }
 }
 
-func require_LessThan[T constraints.Ordered](t *testing.T, a, b T) {
+func require_LessThan[T ordered](t *testing.T, a, b T) {
  t.Helper()
  if a >= b {
  t.Fatalf("require %v to be less than %v", a, b)
@@ -330,3 +328,17 @@ func runSolicitLeafServerToURL(surl string) (*Server, *Options) {
  o.LeafNode.ReconnectInterval = 100 * time.Millisecond
  return RunServer(&o), &o
 }
+
+// ordered is a constraint that permits any ordered type.
+//
+// To avoid a dependency on go1.21+ or golang.org/x/exp, we copy the ordered
+// interface def from go 1.21.3:src/cmp/cmp.go (https://pkg.go.dev/cmp#Ordered).
+//
+// When this repo is updated to go 1.21+, this should be deleted and references
+// replaced by cmp.Ordered.
+type ordered interface {
+ ~int | ~int8 | ~int16 | ~int32 | ~int64 |
+ ~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr |
+ ~float32 | ~float64 |
+ ~string
+}