plugins: add a release only flag to Discover

Since we now support loading pre-releases, we also want Packer to be
able to ignore them by user demand, so we put in place the
infrastructure to modulate this.

hcl2template/plugin.go

@@ -76,6 +76,7 @@ func (cfg *PackerConfig) DetectPluginBinaries() hcl.Diagnostics {
 			Checksummers: []plugingetter.Checksummer{
 				{Type: "sha256", Hash: sha256.New()},
 			},
+			ReleasesOnly: cfg.parser.PluginConfig.ReleasesOnly,
 		},
 	}
 

packer/plugin-getter/plugins.go

@@ -60,6 +60,10 @@ type BinaryInstallationOptions struct {
 	Ext string
 
 	Checksummers []Checksummer
+
+	// ReleasesOnly may be set by commands like validate or build, and
+	// forces Packer to not consider plugin pre-releases.
+	ReleasesOnly bool
 }
 
 type ListInstallationsOptions struct {
@@ -154,13 +158,18 @@ func (pr Requirement) ListInstallations(opts ListInstallationsOptions) (InstallL
 		// versionsStr now looks like v1.2.3_x5.1 or amazon_v1.2.3_x5.1
 		parts := strings.SplitN(versionsStr, "_", 2)
 		pluginVersionStr, protocolVerionStr := parts[0], parts[1]
-		_, err = version.NewVersion(pluginVersionStr)
+		ver, err := version.NewVersion(pluginVersionStr)
 		if err != nil {
 			// could not be parsed, ignoring the file
 			log.Printf("found %q with an incorrect %q version, ignoring it. %v", path, pluginVersionStr, err)
 			continue
 		}
 
+		if ver.Prerelease() != "" && opts.ReleasesOnly {
+			log.Printf("ignoring pre-release plugin %q", path)
+			continue
+		}
+
 		matches := pluginVersionRegex.FindStringSubmatch(pluginVersionStr)
 		if matches == nil {
 			log.Printf("invalid version found: %q, ignoring", pluginVersionStr)

packer/plugin.go

@@ -34,6 +34,7 @@ type PluginConfig struct {
 	Provisioners    ProvisionerSet
 	PostProcessors  PostProcessorSet
 	DataSources     DatasourceSet
+	ReleasesOnly    bool
 }
 
 // PACKERSPACE is used to represent the spaces that separate args for a command
@@ -81,6 +82,7 @@ func (c *PluginConfig) Discover() error {
 			Checksummers: []plugingetter.Checksummer{
 				{Type: "sha256", Hash: sha256.New()},
 			},
+			ReleasesOnly: c.ReleasesOnly,
 		},
 	})
 	if err != nil {