hcl2_upgrade: add required_plugins in out template

When a legacy JSON template references built-in plugins, we add them to
the resulting template as a `required_plugins' block in HCL2.

command/hcl2_upgrade.go

@@ -797,16 +797,93 @@ type PackerParser struct {
 }
 
 func (p *PackerParser) Parse(tpl *template.Template) error {
+	reqPlugins, err := p.generateRequiredPluginsBlock(tpl)
+	if err != nil {
+		return err
+	}
+
+	if tpl.MinVersion == "" && reqPlugins == nil {
+		return nil
+	}
+
+	fileContent := hclwrite.NewEmptyFile()
+	body := fileContent.Body()
+	packerBody := body.AppendNewBlock("packer", nil).Body()
+
 	if tpl.MinVersion != "" {
-		fileContent := hclwrite.NewEmptyFile()
-		body := fileContent.Body()
-		packerBody := body.AppendNewBlock("packer", nil).Body()
 		packerBody.SetAttributeValue("required_version", cty.StringVal(fmt.Sprintf(">= %s", tpl.MinVersion)))
-		p.out = fileContent.Bytes()
 	}
+
+	if reqPlugins != nil {
+		packerBody.AppendBlock(reqPlugins)
+	}
+
+	p.out = fileContent.Bytes()
+
 	return nil
 }
 
+func gatherPluginsFromTemplate(tpl *template.Template) []string {
+	plugins := map[string]struct{}{}
+
+	for _, b := range tpl.Builders {
+		for prefix, plugin := range knownPluginPrefixes {
+			if strings.HasPrefix(b.Type, prefix) {
+				plugins[plugin] = struct{}{}
+			}
+		}
+	}
+
+	for _, p := range tpl.Provisioners {
+		for prefix, plugin := range knownPluginPrefixes {
+			if strings.HasPrefix(p.Type, prefix) {
+				plugins[plugin] = struct{}{}
+			}
+		}
+	}
+
+	for _, pps := range tpl.PostProcessors {
+		for _, pp := range pps {
+			for prefix, plugin := range knownPluginPrefixes {
+				if strings.HasPrefix(pp.Type, prefix) {
+					plugins[plugin] = struct{}{}
+				}
+			}
+		}
+	}
+
+	if len(plugins) == 0 {
+		return nil
+	}
+
+	retPlugins := make([]string, 0, len(plugins))
+	for plugin := range plugins {
+		retPlugins = append(retPlugins, plugin)
+	}
+
+	sort.Strings(retPlugins)
+
+	return retPlugins
+}
+
+func (p *PackerParser) generateRequiredPluginsBlock(tpl *template.Template) (*hclwrite.Block, error) {
+	plugins := gatherPluginsFromTemplate(tpl)
+	if len(plugins) == 0 {
+		return nil, nil
+	}
+
+	reqPlugins := hclwrite.NewBlock("required_plugins", nil)
+	for _, plugin := range plugins {
+		pluginBlock := cty.ObjectVal(map[string]cty.Value{
+			"source":  cty.StringVal(plugin),
+			"version": cty.StringVal("~> 1"),
+		})
+		reqPlugins.Body().SetAttributeValue(strings.Replace(plugin, "github.com/hashicorp/", "", 1), pluginBlock)
+	}
+
+	return reqPlugins, nil
+}
+
 func (p *PackerParser) Write(out *bytes.Buffer) {
 	if len(p.out) > 0 {
 		if p.WithAnnotations {

command/hcl2_upgrade_test.go

@@ -38,6 +38,7 @@ func Test_hcl2_upgrade(t *testing.T) {
 		{folder: "complete-variables-with-template-engine", flags: []string{}},
 		{folder: "undeclared-variables", flags: []string{}, exitCode: 0},
 		{folder: "varfile-with-no-variables-block", flags: []string{}, exitCode: 0},
+		{folder: "bundled-plugin-used", flags: []string{}, exitCode: 0},
 	}
 
 	for _, tc := range tc {

command/test-fixtures/hcl2_upgrade/ami_test/expected.pkr.hcl

@@ -1,3 +1,11 @@
+packer {
+  required_plugins {
+    amazon = {
+      source  = "github.com/hashicorp/amazon"
+      version = "~> 1"
+    }
+  }
+}
 
 source "amazon-ebs" "autogenerated_1" {
   run_tags = {

command/test-fixtures/hcl2_upgrade/aws-access-config/expected.pkr.hcl

@@ -1,5 +1,11 @@
 packer {
   required_version = ">= 1.6.0"
+  required_plugins {
+    amazon = {
+      source  = "github.com/hashicorp/amazon"
+      version = "~> 1"
+    }
+  }
 }
 
 variable "aws_access_key" {

command/test-fixtures/hcl2_upgrade/azure_shg/expected.pkr.hcl

@@ -1,3 +1,11 @@
+packer {
+  required_plugins {
+    azure = {
+      source  = "github.com/hashicorp/azure"
+      version = "~> 1"
+    }
+  }
+}
 
 source "azure-arm" "autogenerated_1" {
   shared_image_gallery {

command/test-fixtures/hcl2_upgrade/bundled-plugin-used/expected.pkr.hcl

@@ -0,0 +1,29 @@
+packer {
+  required_plugins {
+    amazon = {
+      source  = "github.com/hashicorp/amazon"
+      version = "~> 1"
+    }
+    ansible = {
+      source  = "github.com/hashicorp/ansible"
+      version = "~> 1"
+    }
+    googlecompute = {
+      source  = "github.com/hashicorp/googlecompute"
+      version = "~> 1"
+    }
+  }
+}
+
+source "amazon-ebs" "autogenerated_1" {
+}
+
+build {
+  sources = ["source.amazon-ebs.autogenerated_1"]
+
+  provisioner "ansible-local" {
+  }
+
+  post-processor "googlecompute-import" {
+  }
+}

command/test-fixtures/hcl2_upgrade/bundled-plugin-used/input.json

@@ -0,0 +1,11 @@
+{
+	"builders": [{
+		"type": "amazon-ebs"
+	}],
+	"provisioners": [{
+		"type": "ansible-local"
+	}],
+	"post-processors": [{
+		"type": "googlecompute-import"
+	}]
+}

command/test-fixtures/hcl2_upgrade/complete/expected.pkr.hcl

@@ -14,6 +14,12 @@
 # See https://www.packer.io/docs/templates/hcl_templates/blocks/packer for more info
 packer {
   required_version = ">= 1.6.0"
+  required_plugins {
+    amazon = {
+      source  = "github.com/hashicorp/amazon"
+      version = "~> 1"
+    }
+  }
 }
 
 # All generated input variables will be of 'string' type as this is how Packer JSON

command/test-fixtures/hcl2_upgrade/minimal/expected.pkr.hcl

@@ -14,6 +14,12 @@
 # See https://www.packer.io/docs/templates/hcl_templates/blocks/packer for more info
 packer {
   required_version = ">= 1.6.0"
+  required_plugins {
+    amazon = {
+      source  = "github.com/hashicorp/amazon"
+      version = "~> 1"
+    }
+  }
 }
 
 # All generated input variables will be of 'string' type as this is how Packer JSON

command/test-fixtures/hcl2_upgrade/source-name/expected.pkr.hcl

@@ -14,6 +14,12 @@
 # See https://www.packer.io/docs/templates/hcl_templates/blocks/packer for more info
 packer {
   required_version = ">= 1.6.0"
+  required_plugins {
+    amazon = {
+      source  = "github.com/hashicorp/amazon"
+      version = "~> 1"
+    }
+  }
 }
 
 # All generated input variables will be of 'string' type as this is how Packer JSON

command/test-fixtures/hcl2_upgrade/vsphere_linux_options_and_network_interface/expected.pkr.hcl

@@ -1,3 +1,11 @@
+packer {
+  required_plugins {
+    vsphere = {
+      source  = "github.com/hashicorp/vsphere"
+      version = "~> 1"
+    }
+  }
+}
 
 source "vsphere-clone" "autogenerated_1" {
   RAM_reserve_all     = false

command/test-fixtures/hcl2_upgrade/without-annotations/expected.pkr.hcl

@@ -1,5 +1,11 @@
 packer {
   required_version = ">= 1.6.0"
+  required_plugins {
+    amazon = {
+      source  = "github.com/hashicorp/amazon"
+      version = "~> 1"
+    }
+  }
 }
 
 variable "aws_access_key" {