plugins: rely more on version lib for checks

When discovering the installed plugins locally, we perform a couple of
checks on the version, namely that it is valid, if it is a prerelease,
it needs to be a dev, and that the self-reported version matches the one
hinted at through the name of the binary.

This was done through regexes, but those were a wee bit simple when
dealing with versions that have metadata. Those binaries would be
completely ignored by Packer, and never loaded, although they are a
valid use case.

The version library we already used supports those however, and
comparisons are more reliable with them.
So, in order to simplify our code, and make it more reliable, we're
exclusively using this library to perform parsing and comparisons of
versions during the discovery phase.

packer/plugin-getter/plugins.go

@@ -100,8 +100,6 @@ func (opts BinaryInstallationOptions) FilenameSuffix() string {
 	return "_" + opts.OS + "_" + opts.ARCH + opts.Ext
 }
 
-var pluginVersionRegex = regexp.MustCompile(`^v([0-9]+\.[0-9]+\.[0-9]+)(-dev)?$`)
-
 // ListInstallations lists unique installed versions of plugin Requirement pr
 // with opts as a filter.
 //
@@ -170,30 +168,35 @@ func (pr Requirement) ListInstallations(opts ListInstallationsOptions) (InstallL
 			continue
 		}
 
-		matches := pluginVersionRegex.FindStringSubmatch(pluginVersionStr)
-		if matches == nil {
-			log.Printf("invalid version found: %q, ignoring", pluginVersionStr)
+		rawVersion, err := version.NewVersion(pluginVersionStr)
+		if err != nil {
+			log.Printf("malformed version string in filename %q: %s, ignoring", pluginVersionStr, err)
 			continue
 		}
 
-		absVersion := matches[1]
-		if len(matches) == 3 {
-			absVersion = fmt.Sprintf("%s%s", absVersion, matches[2])
+		descVersion, err := version.NewVersion(describeInfo.Version)
+		if err != nil {
+			log.Printf("malformed reported version string %q: %s, ignoring", describeInfo.Version, err)
+			continue
 		}
 
-		if absVersion != describeInfo.Version {
-			log.Printf("plugin %q reported version %s while its name implies version %s, ignoring", path, describeInfo.Version, absVersion)
+		if rawVersion.Compare(descVersion) != 0 {
+			log.Printf("plugin %q reported version %q while its name implies version %q, ignoring", path, describeInfo.Version, pluginVersionStr)
 			continue
 		}
 
-		rawVersion, _ := version.NewVersion(matches[1])
+		preRel := descVersion.Prerelease()
+		if preRel != "" && preRel != "dev" {
+			log.Printf("invalid plugin pre-release version %q, only development or release binaries are accepted", pluginVersionStr)
+		}
+
 		// no constraint means always pass, this will happen for implicit
 		// plugin requirements and when we list all plugins.
 		//
 		// Note: we use the raw version name here, without the pre-release
 		// suffix, as otherwise constraints reject them, which is not
 		// what we want by default.
-		if !pr.VersionConstraints.Check(rawVersion) {
+		if !pr.VersionConstraints.Check(rawVersion.Core()) {
 			log.Printf("[TRACE] version %q of file %q does not match constraint %q", pluginVersionStr, path, pr.VersionConstraints.String())
 			continue
 		}