internal/frontend: fix major version for std

Display the major version as "go1", not "v1".

Also, fix the tooltip.

Fixes b/143529585.
Fixes b/143613230.

Change-Id: I3379e8295a90f79c375f6e54e3593eee2391a335
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/589902
CI-Result: Cloud Build <devtools-proctor-result-processor@system.gserviceaccount.com>
Reviewed-by: Julie Qiu <julieqiu@google.com>

internal/frontend/versions.go

@@ -160,6 +160,13 @@ func buildVersionDetails(currentModulePath string, versions []*internal.VersionI
 		// we detect a +incompatible version (when the path version does not match
 		// the sematic version), we prefer the path version.
 		major := semver.Major(v.Version)
+		if v.ModulePath == stdlib.ModulePath {
+			var err error
+			major, err = stdlib.MajorVersionForVersion(v.Version)
+			if err != nil {
+				panic(err)
+			}
+		}
 		if _, pathMajor, ok := module.SplitPathVersion(v.ModulePath); ok {
 			// We prefer the path major version except for v1 import paths where the
 			// semver major version is v0. In this case, we prefer the more specific
@@ -169,7 +176,7 @@ func buildVersionDetails(currentModulePath string, versions []*internal.VersionI
 				// Trim both '/' and '.' from the path major version to account for
 				// standard and gopkg.in module paths.
 				major = strings.TrimLeft(pathMajor, "/.")
-			} else if major != "v0" {
+			} else if major != "v0" && !strings.HasPrefix(major, "go") {
 				major = "v1"
 			}
 		}
@@ -187,14 +194,15 @@ func buildVersionDetails(currentModulePath string, versions []*internal.VersionI
 		majorTree.forEach(func(_ string, minorTree *versionTree) {
 			patches := []*VersionSummary{}
 			minorTree.forEach(func(_ string, patchTree *versionTree) {
-				var formattedVersion string
+
+				version := patchTree.versionInfo.Version
+				formattedVersion := formatVersion(version)
 				if patchTree.versionInfo.ModulePath == stdlib.ModulePath {
 					formattedVersion = goTagForVersion(patchTree.versionInfo.Version)
-				} else {
-					formattedVersion = formatVersion(patchTree.versionInfo.Version)
+					version = formattedVersion
 				}
 				patches = append(patches, &VersionSummary{
-					Version:          patchTree.versionInfo.Version,
+					Version:          version,
 					Link:             linkify(patchTree.versionInfo),
 					CommitTime:       elapsedTime(patchTree.versionInfo.CommitTime),
 					FormattedVersion: formattedVersion,

internal/frontend/versions_test.go

@@ -12,7 +12,6 @@ import (
 	"golang.org/x/discovery/internal"
 	"golang.org/x/discovery/internal/postgres"
 	"golang.org/x/discovery/internal/sample"
-	"golang.org/x/discovery/internal/stdlib"
 	"golang.org/x/discovery/internal/version"
 )
 
@@ -40,7 +39,7 @@ func versionSummaries(path string, versions [][]string, linkify func(path, versi
 		for j, version := range pointVersions {
 			var semver, formattedVersion string
 			if inStdLib(path) {
-				semver = stdlib.VersionForTag(version)
+				semver = version
 				formattedVersion = version
 			} else {
 				semver = version
@@ -238,7 +237,7 @@ func TestFetchPackageVersionsDetails(t *testing.T) {
 			wantDetails: &VersionsDetails{
 				ThisModule: []*MajorVersionGroup{
 					{
-						Major:      "v1",
+						Major:      "go1",
 						ModulePath: "std",
 						Versions: packageVersionSummaries("net/http", "std", [][]string{
 							{"go1.12.5"},

internal/stdlib/stdlib.go

@@ -105,6 +105,22 @@ func TagForVersion(version string) (_ string, err error) {
 	return goVersion, nil
 }
 
+// MajorVersionForVersion returns the Go major version for version.
+// E.g. "v1.13.3" => "go1".
+func MajorVersionForVersion(version string) (_ string, err error) {
+	defer derrors.Wrap(&err, "MajorTagForVersion(%q)", version)
+
+	tag, err := TagForVersion(version)
+	if err != nil {
+		return "", err
+	}
+	i := strings.IndexRune(tag, '.')
+	if i < 0 {
+		return "", fmt.Errorf("no '.' in go tag %q", tag)
+	}
+	return tag[:i], nil
+}
+
 // finalDigitsIndex returns the index of the first digit in the sequence of digits ending s.
 // If s doesn't end in digits, it returns -1.
 func finalDigitsIndex(s string) int {

internal/stdlib/stdlib_test.go

@@ -83,6 +83,27 @@ func TestTagForVersion(t *testing.T) {
 	}
 }
 
+func TestMajorVersionForVersion(t *testing.T) {
+	for _, test := range []struct {
+		in   string
+		want string // empty => error
+	}{
+		{"", ""},
+		{"garbage", ""},
+		{"v1.13.3", "go1"},
+		{"v1.9.0-rc.2", "go1"},
+		{"v2.1.3", "go2"},
+	} {
+		got, err := MajorVersionForVersion(test.in)
+		if (err != nil) != (test.want == "") {
+			t.Errorf("%q: err: got %v, wanted error: %t", test.in, err, test.want == "")
+		}
+		if err == nil && got != test.want {
+			t.Errorf("%q: got %q, want %q", test.in, got, test.want)
+		}
+	}
+}
+
 func TestZip(t *testing.T) {
 	UseTestData = true
 	defer func() { UseTestData = false }()