cmd/go/internal/mvs: omit modules at version "none" in BuildList and Req

For #37438

Change-Id: Icb28035ae4027aa09d8959d4ac2f4b94a6c843a7
Reviewed-on: https://go-review.googlesource.com/c/go/+/266339
Run-TryBot: Bryan C. Mills <[email protected]>
Reviewed-by: Jay Conrod <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Trust: Bryan C. Mills <[email protected]>

Author: Bryan C. Mills

src/cmd/go/internal/mvs/mvs.go

@@ -120,7 +120,9 @@ func buildList(target module.Version, reqs Reqs, upgrade func(module.Version) (m
 		}
 		node.required = required
 		for _, r := range node.required {
-			work.Add(r)
+			if r.Version != "none" {
+				work.Add(r)
+			}
 		}
 
 		if upgrade != nil {
@@ -208,6 +210,9 @@ func buildList(target module.Version, reqs Reqs, upgrade func(module.Version) (m
 		n := modGraph[module.Version{Path: path, Version: vers}]
 		required := n.required
 		for _, r := range required {
+			if r.Version == "none" {
+				continue
+			}
 			v := min[r.Path]
 			if r.Path != target.Path && reqs.Max(v, r.Version) != v {
 				panic(fmt.Sprintf("mistake: version %q does not satisfy requirement %+v", v, r)) // TODO: Don't panic.

src/cmd/go/internal/mvs/mvs_test.go

@@ -317,6 +317,13 @@ B1: X2
 X1: I1
 X2: 
 req M: A1 B1
+
+name: reqnone
+M: Anone B1 D1 E1
+B1: Cnone D1
+E1: Fnone
+build M: M B1 D1 E1
+req M: B1 E1
 `
 
 func Test(t *testing.T) {