cmd/go/internal/modfetch: filter pseudo-versions from proxy /list endpoints

The /list files in the module cache include pseudo-versions, but the
documentation for (*modfetch).Repo.Versions explicitly states that
they are not included in the output of that method.

Fixes #32715

Change-Id: Ieba1500b91f52b5fa689e70e16dbe3ad40de20f7
Reviewed-on: https://go-review.googlesource.com/c/go/+/183402
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

src/cmd/go/internal/modfetch/proxy.go

@@ -251,7 +251,7 @@ func (p *proxyRepo) Versions(prefix string) ([]string, error) {
 	var list []string
 	for _, line := range strings.Split(string(data), "\n") {
 		f := strings.Fields(line)
-		if len(f) >= 1 && semver.IsValid(f[0]) && strings.HasPrefix(f[0], prefix) {
+		if len(f) >= 1 && semver.IsValid(f[0]) && strings.HasPrefix(f[0], prefix) && !IsPseudoVersion(f[0]) {
 			list = append(list, f[0])
 		}
 	}
@@ -264,14 +264,36 @@ func (p *proxyRepo) latest() (*RevInfo, error) {
 	if err != nil {
 		return nil, p.versionError("", err)
 	}
-	var best time.Time
-	var bestVersion string
+
+	var (
+		bestTime             time.Time
+		bestTimeIsFromPseudo bool
+		bestVersion          string
+	)
+
 	for _, line := range strings.Split(string(data), "\n") {
 		f := strings.Fields(line)
-		if len(f) >= 2 && semver.IsValid(f[0]) {
-			ft, err := time.Parse(time.RFC3339, f[1])
-			if err == nil && best.Before(ft) {
-				best = ft
+		if len(f) >= 1 && semver.IsValid(f[0]) {
+			// If the proxy includes timestamps, prefer the timestamp it reports.
+			// Otherwise, derive the timestamp from the pseudo-version.
+			var (
+				ft             time.Time
+				ftIsFromPseudo = false
+			)
+			if len(f) >= 2 {
+				ft, _ = time.Parse(time.RFC3339, f[1])
+			} else if IsPseudoVersion(f[0]) {
+				ft, _ = PseudoVersionTime(f[0])
+				ftIsFromPseudo = true
+			} else {
+				// Repo.Latest promises that this method is only called where there are
+				// no tagged versions. Ignore any tagged versions that were added in the
+				// meantime.
+				continue
+			}
+			if bestTime.Before(ft) {
+				bestTime = ft
+				bestTimeIsFromPseudo = ftIsFromPseudo
 				bestVersion = f[0]
 			}
 		}
@@ -279,13 +301,23 @@ func (p *proxyRepo) latest() (*RevInfo, error) {
 	if bestVersion == "" {
 		return nil, p.versionError("", codehost.ErrNoCommits)
 	}
-	info := &RevInfo{
+
+	if bestTimeIsFromPseudo {
+		// We parsed bestTime from the pseudo-version, but that's in UTC and we're
+		// supposed to report the timestamp as reported by the VCS.
+		// Stat the selected version to canonicalize the timestamp.
+		//
+		// TODO(bcmills): Should we also stat other versions to ensure that we
+		// report the correct Name and Short for the revision?
+		return p.Stat(bestVersion)
+	}
+
+	return &RevInfo{
 		Version: bestVersion,
 		Name:    bestVersion,
 		Short:   bestVersion,
-		Time:    best,
-	}
-	return info, nil
+		Time:    bestTime,
+	}, nil
 }
 
 func (p *proxyRepo) Stat(rev string) (*RevInfo, error) {

src/cmd/go/testdata/mod/github.com_dmitshur-test_modtest5_v0.0.0-20190619020302-197a620e0c9a.txt

@@ -0,0 +1,10 @@
+module github.com/dmitshur-test/modtest5@v0.0.0-20190619020302-197a620e0c9a
+
+-- .mod --
+module github.com/dmitshur-test/modtest5
+-- .info --
+{"Version":"v0.0.0-20190619020302-197a620e0c9a","Time":"2019-06-18T19:03:02-07:00"}
+-- p.go --
+package p
+
+const v = 1

src/cmd/go/testdata/mod/github.com_dmitshur-test_modtest5_v0.5.0-alpha.0.20190619023908-3da23a9deb9e.txt

@@ -0,0 +1,10 @@
+module github.com/dmitshur-test/modtest5@v0.5.0-alpha.0.20190619023908-3da23a9deb9e
+
+-- .mod --
+module github.com/dmitshur-test/modtest5
+-- .info --
+{"Version":"v0.5.0-alpha.0.20190619023908-3da23a9deb9e","Time":"2019-06-18T19:39:08-07:00"}
+-- p.go --
+package p
+
+const v = 3

src/cmd/go/testdata/mod/github.com_dmitshur-test_modtest5_v0.5.0-alpha.txt

@@ -0,0 +1,10 @@
+module github.com/dmitshur-test/modtest5@v0.5.0-alpha
+
+-- .mod --
+module github.com/dmitshur-test/modtest5
+-- .info --
+{"Version":"v0.5.0-alpha","Time":"2019-06-18T19:04:46-07:00"}
+-- p.go --
+package p
+
+const v = 2

src/cmd/go/testdata/script/mod_list_pseudo.txt

@@ -0,0 +1,50 @@
+env GO111MODULE=on
+
+# Regression test for golang.org/issue/32715.
+
+# When using $GOPATH/pkg/mod/cache/download as a proxy,
+# 'latest' queries should prefer tagged versions over pseudo-versions.
+
+go mod download github.com/dmitshur-test/modtest5@v0.0.0-20190619020302-197a620e0c9a
+go mod download github.com/dmitshur-test/modtest5@v0.5.0-alpha
+go mod download github.com/dmitshur-test/modtest5@v0.5.0-alpha.0.20190619023908-3da23a9deb9e
+cmp $GOPATH/pkg/mod/cache/download/github.com/dmitshur-test/modtest5/@v/list $WORK/modtest5.list
+
+env GOPROXY=file:///$GOPATH/pkg/mod/cache/download
+env GOPATH=$WORK/gopath2
+mkdir $GOPATH
+
+go list -m -json github.com/dmitshur-test/modtest5@latest
+cmp stdout $WORK/modtest5.json
+
+# If the module proxy contains only pseudo-versions, 'latest' should stat
+# the version with the most recent timestamp — not the highest semantic
+# version — and return its metadata.
+env GOPROXY=file:///$WORK/tinyproxy
+go list -m -json dmitri.shuralyov.com/test/modtest3@latest
+cmp stdout $WORK/modtest3.json
+
+-- $WORK/modtest5.list --
+v0.0.0-20190619020302-197a620e0c9a
+v0.5.0-alpha
+v0.5.0-alpha.0.20190619023908-3da23a9deb9e
+-- $WORK/modtest5.json --
+{
+	"Path": "github.com/dmitshur-test/modtest5",
+	"Version": "v0.5.0-alpha",
+	"Time": "2019-06-18T19:04:46-07:00"
+}
+-- $WORK/tinyproxy/dmitri.shuralyov.com/test/modtest3/@v/list --
+v0.1.0-0.20161023043300-000000000000
+v0.0.0-20181023043359-a85b471d5412
+-- $WORK/tinyproxy/dmitri.shuralyov.com/test/modtest3/@v/v0.0.0-20181023043359-a85b471d5412.info --
+{
+	"Version": "v0.0.0-20181023043359-a85b471d5412",
+	"Time": "2018-10-22T21:33:59-07:00"
+}
+-- $WORK/modtest3.json --
+{
+	"Path": "dmitri.shuralyov.com/test/modtest3",
+	"Version": "v0.0.0-20181023043359-a85b471d5412",
+	"Time": "2018-10-22T21:33:59-07:00"
+}