internal/frontend: enable requests to std@master

Requests to pkg.go.dev/std@master are now supported.

For golang/go#44390

Change-Id: Ie64ea679bfe855aa690004bf6effd7be424aa5dc
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/294832
Trust: Julie Qiu <[email protected]>
Reviewed-by: Jamal Carvalho <[email protected]>

Author: julieqiu

internal/frontend/urlinfo.go

@@ -182,7 +182,7 @@ func checkExcluded(ctx context.Context, ds internal.DataSource, fullPath string)
 // isSupportedVersion reports whether the version is supported by the frontend.
 func isSupportedVersion(fullPath, requestedVersion string) bool {
 	if _, ok := internal.DefaultBranches[requestedVersion]; ok {
-		return !stdlib.Contains(fullPath)
+		return !stdlib.Contains(fullPath) || requestedVersion == "master"
 	}
 	return requestedVersion == internal.LatestVersion || semver.IsValid(requestedVersion)
 }

internal/frontend/urlinfo_test.go

@@ -218,7 +218,7 @@ func TestIsSupportedVersion(t *testing.T) {
 		{"net/http", "v1.2.3", true}, // isSupportedVersion expects the goTag is already converted to semver
 		{"net/http", "v1.2.3.bad", false},
 		{"net/http", "latest", true},
-		{"net/http", "master", false},
+		{"net/http", "master", true},
 		{"net/http", "main", false},
 	}
 	for _, test := range tests {

internal/frontend/versions.go

@@ -276,6 +276,9 @@ func pseudoVersionRev(v string) string {
 // displayVersion returns the version string, formatted for display.
 func displayVersion(v string, modulePath string) string {
 	if modulePath == stdlib.ModulePath {
+		if strings.HasPrefix(v, "v0.0.0") {
+			return strings.Split(v, "-")[2]
+		}
 		return goTagForVersion(v)
 	}
 	return formatVersion(v)