cmd/go/internal/modload: make 'list -u' consider current pseudoversion

As pointed out by thepudds in #30634, the 'list -u' documentation states that the current version should be considered for upgrade:
The -u flag adds information about available upgrades. When the latest version of a given module is newer than the current one, list -u sets the Module's Update field to information about the newer module.

In go 1.12.4 (and current tip), an older version will be suggested as upgrade to a newer pseudo version.

Updates: #30634

Change-Id: If2c8887198884b8e7ccb3a604908065aa1f1878a
Reviewed-on: https://go-review.googlesource.com/c/go/+/174206
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

1 files changed, 10 insertions, 7 deletions

diff --git a/src/cmd/go/internal/modload/build.go b/src/cmd/go/internal/modload/build.go
index a41b176ccd..66a0a75d96 100644
--- a/src/cmd/go/internal/modload/build.go
+++ b/src/cmd/go/internal/modload/build.go
@@ -12,6 +12,7 @@ import (
 	"cmd/go/internal/modinfo"
 	"cmd/go/internal/module"
 	"cmd/go/internal/search"
+	"cmd/go/internal/semver"
 	"encoding/hex"
 	"fmt"
 	"internal/goroot"
@@ -74,13 +75,15 @@ func ModuleInfo(path string) *modinfo.ModulePublic {
 
 // addUpdate fills in m.Update if an updated version is available.
 func addUpdate(m *modinfo.ModulePublic) {
-	if m.Version != "" {
-		if info, err := Query(m.Path, "latest", Allowed); err == nil && info.Version != m.Version {
-			m.Update = &modinfo.ModulePublic{
-				Path:    m.Path,
-				Version: info.Version,
-				Time:    &info.Time,
-			}
+	if m.Version == "" {
+		return
+	}
+
+	if info, err := Query(m.Path, "latest", Allowed); err == nil && semver.Compare(info.Version, m.Version) > 0 {
+		m.Update = &modinfo.ModulePublic{
+			Path:    m.Path,
+			Version: info.Version,
+			Time:    &info.Time,
 		}
 	}
 }