command: add --force option to init/install

The --force option for packer init and packer plugins install enforces
installation of a plugin, even if it is already locally installed.

This will become useful if for some reason a pre-existing plugin
binary/version is already installed, and we want to overwrite it.

command/cli.go

@@ -104,6 +104,7 @@ type BuildArgs struct {
 
 func (ia *InitArgs) AddFlagSets(flags *flag.FlagSet) {
 	flags.BoolVar(&ia.Upgrade, "upgrade", false, "upgrade any present plugin to the highest allowed version.")
+	flags.BoolVar(&ia.Force, "force", false, "force installation of a plugin, even if already installed")
 
 	ia.MetaArgs.AddFlagSets(flags)
 }
@@ -112,6 +113,7 @@ func (ia *InitArgs) AddFlagSets(flags *flag.FlagSet) {
 type InitArgs struct {
 	MetaArgs
 	Upgrade bool
+	Force   bool
 }
 
 // PluginsRequiredArgs represents a parsed cli line for a `packer plugins required <path>`

command/init.go

@@ -130,6 +130,7 @@ for more info.`)
 			InFolders:                 opts.FromFolders,
 			BinaryInstallationOptions: opts.BinaryInstallationOptions,
 			Getters:                   getters,
+			Force:                     cla.Force,
 		})
 		if err != nil {
 			c.Ui.Error(fmt.Sprintf("Failed getting the %q plugin:", pluginRequirement.Identifier))
@@ -163,6 +164,8 @@ Options:
                                version, if there is a new higher one. Note that
                                this still takes into consideration the version
                                constraint of the config.
+  -force                       Forces installation of plugins, even if already
+                               installed.
 `
 
 	return strings.TrimSpace(helpText)

command/plugins_install.go

@@ -50,6 +50,7 @@ Options:
                  installs the plugin where a normal invocation would, but will
 	         not try to download it from a web server, but instead directly
 	         install the binary for Packer to be able to load it later on.
+  - force:       forces installation of a plugin, even if it is already there.
 `
 
 	return strings.TrimSpace(helpText)
@@ -72,10 +73,12 @@ type PluginsInstallArgs struct {
 	PluginName string
 	PluginPath string
 	Version    string
+	Force      bool
 }
 
 func (pa *PluginsInstallArgs) AddFlagSets(flags *flag.FlagSet) {
 	flags.StringVar(&pa.PluginPath, "path", "", "install the plugin from a specific path")
+	flags.BoolVar(&pa.Force, "force", false, "force installation of a plugin, even if already installed")
 	pa.MetaArgs.AddFlagSets(flags)
 }
 
@@ -168,6 +171,7 @@ func (c *PluginsInstallCommand) RunContext(buildCtx context.Context, args *Plugi
 		InFolders:                 opts.FromFolders,
 		BinaryInstallationOptions: opts.BinaryInstallationOptions,
 		Getters:                   getters,
+		Force:                     args.Force,
 	})
 
 	if err != nil {

packer/plugin-getter/plugins.go

@@ -244,6 +244,9 @@ type InstallOptions struct {
 	// folder of this list.
 	InFolders []string
 
+	// Forces installation of the plugin, even if already installed.
+	Force bool
+
 	BinaryInstallationOptions
 }
 
@@ -582,7 +585,7 @@ func (pr *Requirement) InstallLatest(opts InstallOptions) (*Installation, error)
 
 								log.Printf("[TRACE] found a pre-exising %q checksum file", potentialChecksumer.Type)
 								// if outputFile is there and matches the checksum: do nothing more.
-								if err := localChecksum.ChecksumFile(localChecksum.Expected, potentialOutputFilename); err == nil {
+								if err := localChecksum.ChecksumFile(localChecksum.Expected, potentialOutputFilename); err == nil && !opts.Force {
 									log.Printf("[INFO] %s v%s plugin is already correctly installed in %q", pr.Identifier, version, potentialOutputFilename)
 									return nil, nil // success
 								}

packer/plugin-getter/plugins_test.go

@@ -349,6 +349,7 @@ func TestRequirement_InstallLatest(t *testing.T) {
 					pluginFolderOne,
 					pluginFolderTwo,
 				},
+				false,
 				BinaryInstallationOptions{
 					APIVersionMajor: "5", APIVersionMinor: "0",
 					OS: "darwin", ARCH: "amd64",
@@ -385,6 +386,7 @@ func TestRequirement_InstallLatest(t *testing.T) {
 					pluginFolderOne,
 					pluginFolderTwo,
 				},
+				false,
 				BinaryInstallationOptions{
 					APIVersionMajor: "5", APIVersionMinor: "1",
 					OS: "darwin", ARCH: "amd64",
@@ -430,6 +432,7 @@ func TestRequirement_InstallLatest(t *testing.T) {
 					pluginFolderOne,
 					pluginFolderTwo,
 				},
+				false,
 				BinaryInstallationOptions{
 					APIVersionMajor: "5", APIVersionMinor: "0",
 					OS: "darwin", ARCH: "amd64",
@@ -477,6 +480,7 @@ func TestRequirement_InstallLatest(t *testing.T) {
 					pluginFolderOne,
 					pluginFolderTwo,
 				},
+				false,
 				BinaryInstallationOptions{
 					APIVersionMajor: "6", APIVersionMinor: "1",
 					OS: "darwin", ARCH: "amd64",
@@ -527,6 +531,7 @@ func TestRequirement_InstallLatest(t *testing.T) {
 					pluginFolderOne,
 					pluginFolderTwo,
 				},
+				false,
 				BinaryInstallationOptions{
 					APIVersionMajor: "6", APIVersionMinor: "1",
 					OS: "darwin", ARCH: "amd64",
@@ -577,6 +582,7 @@ func TestRequirement_InstallLatest(t *testing.T) {
 					pluginFolderOne,
 					pluginFolderTwo,
 				},
+				false,
 				BinaryInstallationOptions{
 					APIVersionMajor: "6", APIVersionMinor: "1",
 					OS: "linux", ARCH: "amd64",
@@ -621,6 +627,7 @@ func TestRequirement_InstallLatest(t *testing.T) {
 					pluginFolderOne,
 					pluginFolderTwo,
 				},
+				false,
 				BinaryInstallationOptions{
 					APIVersionMajor: "6", APIVersionMinor: "1",
 					OS: "darwin", ARCH: "amd64",
@@ -662,6 +669,7 @@ func TestRequirement_InstallLatest(t *testing.T) {
 				[]string{
 					pluginFolderWrongChecksums,
 				},
+				false,
 				BinaryInstallationOptions{
 					APIVersionMajor: "6", APIVersionMinor: "1",
 					OS: "darwin", ARCH: "amd64",