Implicit required_plugin blocks (#10732)

* used components that don't have a required_plugin block will make Packer 'implicitly' require those. These components are manually selected and commented for now.
* add tests
 * docs

command/init.go

@@ -121,12 +121,54 @@ func (c *InitCommand) RunContext(buildCtx context.Context, cla *InitArgs) int {
 			Getters:                   getters,
 		})
 		if err != nil {
+			if pluginRequirement.Implicit {
+				msg := fmt.Sprintf(`
+Warning! At least one component used in your config file(s) has moved out of 
+Packer into the %q plugin.
+For that reason, Packer init tried to install the latest version of the %s 
+plugin. Unfortunately, this failed :
+%s`,
+					pluginRequirement.Identifier,
+					pluginRequirement.Identifier.Type,
+					err)
+				c.Ui.Say(msg)
+			} else {
 				c.Ui.Error(err.Error())
 				ret = 1
 			}
+		}
 		if newInstall != nil {
+			if pluginRequirement.Implicit {
+				msg := fmt.Sprintf("Installed implicitly required plugin %s %s in %q", pluginRequirement.Identifier, newInstall.Version, newInstall.BinaryPath)
+				ui.Say(msg)
+
+				warn := fmt.Sprintf(`
+Warning, at least one component used in your config file(s) has moved out of 
+Packer into the %[2]q plugin and is now being implicitly required. 
+For more details on implicitly required plugins see https://packer.io/docs/commands/init#implicit-required-plugin
+
+To avoid any backward incompatible changes with your
+config file you may want to lock the plugin version by pasting the following to your config:
+
+packer {
+  required_plugins {
+    %[1]s = {
+      source  = "%[2]s"
+      version = "~> %[3]s"
+    }
+  }
+}
+`,
+					pluginRequirement.Identifier.Type,
+					pluginRequirement.Identifier,
+					newInstall.Version,
+				)
+				ui.Error(warn)
+				continue
+			}
 			msg := fmt.Sprintf("Installed plugin %s %s in %q", pluginRequirement.Identifier, newInstall.Version, newInstall.BinaryPath)
 			ui.Say(msg)
+
 		}
 	}
 	return ret

hcl2template/common_test.go

@@ -20,8 +20,8 @@ import (
 
 const lockedVersion = "v1.5.0"
 
-func getBasicParser() *Parser {
+func getBasicParser(opts ...getParserOption) *Parser {
-	return &Parser{
+	parser := &Parser{
 		CorePackerVersion:       version.Must(version.NewSemver(lockedVersion)),
 		CorePackerVersionString: lockedVersion,
 		Parser:                  hclparse.NewParser(),
@@ -44,7 +44,13 @@ func getBasicParser() *Parser {
 			},
 		},
 	}
+	for _, configure := range opts {
+		configure(parser)
 	}
+	return parser
+}
+
+type getParserOption func(*Parser)
 
 type parseTestArgs struct {
 	filename string
@@ -338,7 +344,7 @@ var cmpOpts = []cmp.Option{
 		PackerConfig{},
 		Variable{},
 		SourceBlock{},
-		Datasource{},
+		DatasourceBlock{},
 		ProvisionerBlock{},
 		PostProcessorBlock{},
 		packer.CoreBuild{},

hcl2template/components.go

@@ -0,0 +1,11 @@
+package hcl2template
+
+// ComponentKind helps enumerate what kind of components exist in this Package.
+type ComponentKind int
+
+const (
+	Builder ComponentKind = iota
+	Provisioner
+	PostProcessor
+	Datasource
+)

hcl2template/plugin.go

@@ -41,6 +41,7 @@ func (cfg *PackerConfig) PluginRequirements() (plugingetter.Requirements, hcl.Di
 				Accessor:           name,
 				Identifier:         block.Type,
 				VersionConstraints: block.Requirement.Required,
+				Implicit:           block.PluginDependencyReason == PluginDependencyImplicit,
 			})
 			uniq[name] = block
 		}

hcl2template/types.datasource.go

@@ -11,8 +11,8 @@ import (
 	"github.com/zclconf/go-cty/cty"
 )
 
-// DataBlock references an HCL 'data' block.
+// DatasourceBlock references an HCL 'data' block.
-type Datasource struct {
+type DatasourceBlock struct {
 	Type string
 	Name string
 
@@ -25,9 +25,9 @@ type DatasourceRef struct {
 	Name string
 }
 
-type Datasources map[DatasourceRef]Datasource
+type Datasources map[DatasourceRef]DatasourceBlock
 
-func (data *Datasource) Ref() DatasourceRef {
+func (data *DatasourceBlock) Ref() DatasourceRef {
 	return DatasourceRef{
 		Type: data.Type,
 		Name: data.Name,
@@ -124,9 +124,9 @@ func (cfg *PackerConfig) startDatasource(dataSourceStore packer.DatasourceStore,
 	return datasource, diags
 }
 
-func (p *Parser) decodeDataBlock(block *hcl.Block) (*Datasource, hcl.Diagnostics) {
+func (p *Parser) decodeDataBlock(block *hcl.Block) (*DatasourceBlock, hcl.Diagnostics) {
 	var diags hcl.Diagnostics
-	r := &Datasource{
+	r := &DatasourceBlock{
 		Type:  block.Labels[0],
 		Name:  block.Labels[1],
 		block: block,

hcl2template/types.packer_config_test.go

@@ -131,7 +131,7 @@ func TestParser_complete(t *testing.T) {
 					},
 				},
 				Datasources: Datasources{
-					DatasourceRef{Type: "amazon-ami", Name: "test"}: Datasource{
+					DatasourceRef{Type: "amazon-ami", Name: "test"}: DatasourceBlock{
 						Type:  "amazon-ami",
 						Name:  "test",
 						value: cty.StringVal("foo"),

hcl2template/types.required_plugins.go

@@ -6,6 +6,7 @@ import (
 	"github.com/hashicorp/go-version"
 	"github.com/hashicorp/hcl/v2"
 	"github.com/hashicorp/packer/hcl2template/addrs"
+	"github.com/hashicorp/packer/packer"
 	"github.com/zclconf/go-cty/cty"
 )
 
@@ -41,9 +42,13 @@ func (cfg *PackerConfig) decodeRequiredPluginsBlock(f *hcl.File) hcl.Diagnostics
 }
 
 func (cfg *PackerConfig) decodeImplicitRequiredPluginsBlocks(f *hcl.File) hcl.Diagnostics {
-	// when a plugin is used but not defined in the required plugin blocks, it
+	// when a plugin is used but not available it should be 'implicitly
-	// is 'implicitly used'. Here we read common configuration blocks to try to
+	// required'. Here we read common configuration blocks to try to guess
-	// guess plugins.
+	// plugin usages.
+
+	// decodeRequiredPluginsBlock needs to be called before
+	// decodeImplicitRequiredPluginsBlocks; otherwise all required plugins will
+	// be implicitly required too.
 
 	var diags hcl.Diagnostics
 
@@ -51,14 +56,112 @@ func (cfg *PackerConfig) decodeImplicitRequiredPluginsBlocks(f *hcl.File) hcl.Di
 	diags = append(diags, moreDiags...)
 
 	for _, block := range content.Blocks {
+
 		switch block.Type {
 		case sourceLabel:
-			// TODO
+			diags = append(diags, cfg.decodeImplicitRequiredPluginsBlock(Builder, block)...)
+		case dataSourceLabel:
+			diags = append(diags, cfg.decodeImplicitRequiredPluginsBlock(Datasource, block)...)
+		case buildLabel:
+			content, _, moreDiags := block.Body.PartialContent(buildSchema)
+			diags = append(diags, moreDiags...)
+			for _, block := range content.Blocks {
+
+				switch block.Type {
+				case buildProvisionerLabel:
+					diags = append(diags, cfg.decodeImplicitRequiredPluginsBlock(Provisioner, block)...)
+				case buildPostProcessorLabel:
+					diags = append(diags, cfg.decodeImplicitRequiredPluginsBlock(PostProcessor, block)...)
+				case buildPostProcessorsLabel:
+					content, _, moreDiags := block.Body.PartialContent(postProcessorsSchema)
+					diags = append(diags, moreDiags...)
+					for _, block := range content.Blocks {
+
+						switch block.Type {
+						case buildPostProcessorLabel:
+							diags = append(diags, cfg.decodeImplicitRequiredPluginsBlock(PostProcessor, block)...)
+						}
+					}
+				}
+			}
+
 		}
 	}
 	return diags
 }
 
+func (cfg *PackerConfig) decodeImplicitRequiredPluginsBlock(k ComponentKind, block *hcl.Block) hcl.Diagnostics {
+	if len(block.Labels) == 0 {
+		// malformed block ? Let's not panic :)
+		return nil
+	}
+	// Currently all block types are `type "component-kind" ["name"] {`
+	// this makes this simple.
+	componentName := block.Labels[0]
+
+	store := map[ComponentKind]packer.BasicStore{
+		Builder:       cfg.parser.PluginConfig.Builders,
+		PostProcessor: cfg.parser.PluginConfig.PostProcessors,
+		Provisioner:   cfg.parser.PluginConfig.Provisioners,
+		Datasource:    cfg.parser.PluginConfig.DataSources,
+	}[k]
+	if store.Has(componentName) {
+		// If any core or pre-loaded plugin defines the `happycloud-uploader`
+		// pp, skip. This happens for core and manually installed plugins, as
+		// they will be listed in the PluginConfig before parsing any HCL.
+		return nil
+	}
+
+	redirect := map[ComponentKind]map[string]string{
+		Builder:       cfg.parser.PluginConfig.BuilderRedirects,
+		PostProcessor: cfg.parser.PluginConfig.PostProcessorRedirects,
+		Provisioner:   cfg.parser.PluginConfig.ProvisionerRedirects,
+		Datasource:    cfg.parser.PluginConfig.DatasourceRedirects,
+	}[k][componentName]
+
+	if redirect == "" {
+		// no known redirect for this component
+		return nil
+	}
+
+	redirectAddr, diags := addrs.ParsePluginSourceString(redirect)
+	if diags.HasErrors() {
+		// This should never happen, since the map is manually filled.
+		return diags
+	}
+
+	for _, req := range cfg.Packer.RequiredPlugins {
+		if _, found := req.RequiredPlugins[redirectAddr.Type]; found {
+			// This could happen if a plugin was forked. For example, I forked
+			// the github.com/hashicorp/happycloud plugin into
+			// github.com/azr/happycloud that is required in my config file; and
+			// am using the `happycloud-uploader` pp component from it. In that
+			// case - and to avoid miss-requires - we won't implicitly import
+			// any other `happycloud` plugin.
+			return nil
+		}
+	}
+
+	cfg.implicitlyRequirePlugin(redirectAddr)
+	return nil
+}
+
+func (cfg *PackerConfig) implicitlyRequirePlugin(plugin *addrs.Plugin) {
+	cfg.Packer.RequiredPlugins = append(cfg.Packer.RequiredPlugins, &RequiredPlugins{
+		RequiredPlugins: map[string]*RequiredPlugin{
+			plugin.Type: {
+				Name:   plugin.Type,
+				Source: plugin.String(),
+				Type:   plugin,
+				Requirement: VersionConstraint{
+					Required: nil, // means latest
+				},
+				PluginDependencyReason: PluginDependencyImplicit,
+			},
+		},
+	})
+}
+
 // RequiredPlugin represents a declaration of a dependency on a particular
 // Plugin version or source.
 type RequiredPlugin struct {
@@ -71,8 +174,24 @@ type RequiredPlugin struct {
 	Type        *addrs.Plugin
 	Requirement VersionConstraint
 	DeclRange   hcl.Range
+	PluginDependencyReason
 }
 
+// PluginDependencyReason is an enumeration of reasons why a dependency might be
+// present.
+type PluginDependencyReason int
+
+const (
+	// PluginDependencyExplicit means that there is an explicit
+	// "required_plugin" block in the configuration.
+	PluginDependencyExplicit PluginDependencyReason = iota
+
+	// PluginDependencyImplicit means that there is no explicit
+	// "required_plugin" block but there is at least one resource that uses this
+	// plugin.
+	PluginDependencyImplicit
+)
+
 type RequiredPlugins struct {
 	RequiredPlugins map[string]*RequiredPlugin
 	DeclRange       hcl.Range

hcl2template/types.required_plugins_test.go

@@ -0,0 +1,363 @@
+package hcl2template
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/hashicorp/go-version"
+	"github.com/hashicorp/packer/hcl2template/addrs"
+)
+
+func TestPackerConfig_required_plugin_parse(t *testing.T) {
+
+	tests := []struct {
+		name           string
+		cfg            PackerConfig
+		requirePlugins string
+		restOfTemplate string
+		wantDiags      bool
+		wantConfig     PackerConfig
+	}{
+		{"required_plugin", PackerConfig{parser: getBasicParser()}, `
+		packer {
+			required_plugins {
+				amazon = {
+					source  = "github.com/hashicorp/amazon"
+					version = "~> v1.2.3"
+				}
+			}
+		} `, `
+		source "amazon-ebs" "example" {
+		}
+		`, false, PackerConfig{
+			Packer: struct {
+				VersionConstraints []VersionConstraint
+				RequiredPlugins    []*RequiredPlugins
+			}{
+				RequiredPlugins: []*RequiredPlugins{
+					{RequiredPlugins: map[string]*RequiredPlugin{
+						"amazon": {
+							Name:   "amazon",
+							Source: "github.com/hashicorp/amazon",
+							Type:   &addrs.Plugin{Hostname: "github.com", Namespace: "hashicorp", Type: "amazon"},
+							Requirement: VersionConstraint{
+								Required: mustVersionConstraints(version.NewConstraint("~> v1.2.3")),
+							},
+							PluginDependencyReason: PluginDependencyExplicit,
+						},
+					}},
+				},
+			},
+		}},
+		{"required_plugin_forked_no_redirect", PackerConfig{parser: getBasicParser()}, `
+		packer {
+			required_plugins {
+				amazon = {
+					source  = "github.com/azr/amazon"
+					version = "~> v1.2.3"
+				}
+			}
+		} `, `
+		source "amazon-chroot" "example" {
+		}
+		`, false, PackerConfig{
+			Packer: struct {
+				VersionConstraints []VersionConstraint
+				RequiredPlugins    []*RequiredPlugins
+			}{
+				RequiredPlugins: []*RequiredPlugins{
+					{RequiredPlugins: map[string]*RequiredPlugin{
+						"amazon": {
+							Name:   "amazon",
+							Source: "github.com/azr/amazon",
+							Type:   &addrs.Plugin{Hostname: "github.com", Namespace: "azr", Type: "amazon"},
+							Requirement: VersionConstraint{
+								Required: mustVersionConstraints(version.NewConstraint("~> v1.2.3")),
+							},
+							PluginDependencyReason: PluginDependencyExplicit,
+						},
+					}},
+				},
+			},
+		}},
+		{"required_plugin_forked", PackerConfig{
+			parser: getBasicParser(func(p *Parser) {
+				p.PluginConfig.BuilderRedirects = map[string]string{
+					"amazon-chroot": "github.com/hashicorp/amazon",
+				}
+			},
+			)}, `
+		packer {
+			required_plugins {
+				amazon = {
+					source  = "github.com/azr/amazon"
+					version = "~> v1.2.3"
+				}
+			}
+		} `, `
+		source "amazon-chroot" "example" {
+		}
+		`, false, PackerConfig{
+			Packer: struct {
+				VersionConstraints []VersionConstraint
+				RequiredPlugins    []*RequiredPlugins
+			}{
+				RequiredPlugins: []*RequiredPlugins{
+					{RequiredPlugins: map[string]*RequiredPlugin{
+						"amazon": {
+							Name:   "amazon",
+							Source: "github.com/azr/amazon",
+							Type:   &addrs.Plugin{Hostname: "github.com", Namespace: "azr", Type: "amazon"},
+							Requirement: VersionConstraint{
+								Required: mustVersionConstraints(version.NewConstraint("~> v1.2.3")),
+							},
+							PluginDependencyReason: PluginDependencyExplicit,
+						},
+					}},
+				},
+			},
+		}},
+		{"missing-required-plugin-for-pre-defined-builder", PackerConfig{
+			parser: getBasicParser(func(p *Parser) {
+				p.PluginConfig.BuilderRedirects = map[string]string{
+					"amazon-ebs": "github.com/hashicorp/amazon",
+				}
+			},
+			)},
+			`
+			packer {
+			}`, `
+			# amazon-ebs is mocked in getBasicParser()
+			source "amazon-ebs" "example" {
+			}
+			`,
+			false,
+			PackerConfig{
+				Packer: struct {
+					VersionConstraints []VersionConstraint
+					RequiredPlugins    []*RequiredPlugins
+				}{
+					RequiredPlugins: nil,
+				},
+			}},
+		{"missing-required-plugin-for-builder", PackerConfig{
+			parser: getBasicParser(func(p *Parser) {
+				p.PluginConfig.BuilderRedirects = map[string]string{
+					"amazon-chroot": "github.com/hashicorp/amazon",
+				}
+			},
+			)},
+			`
+			packer {
+			}`, `
+			source "amazon-chroot" "example" {
+			}
+			`,
+			false,
+			PackerConfig{
+				Packer: struct {
+					VersionConstraints []VersionConstraint
+					RequiredPlugins    []*RequiredPlugins
+				}{
+					RequiredPlugins: []*RequiredPlugins{
+						{RequiredPlugins: map[string]*RequiredPlugin{
+							"amazon": {
+								Name:   "amazon",
+								Source: "github.com/hashicorp/amazon",
+								Type:   &addrs.Plugin{Hostname: "github.com", Namespace: "hashicorp", Type: "amazon"},
+								Requirement: VersionConstraint{
+									Required: nil,
+								},
+								PluginDependencyReason: PluginDependencyImplicit,
+							},
+						}},
+					},
+				},
+			}},
+		{"missing-required-plugin-for-provisioner", PackerConfig{
+			parser: getBasicParser(func(p *Parser) {
+				p.PluginConfig.ProvisionerRedirects = map[string]string{
+					"ansible-local": "github.com/ansible/ansible",
+				}
+			},
+			)},
+			`
+			packer {
+			}`, `
+			build {
+				provisioner "ansible-local" {}
+			}
+			`,
+			false,
+			PackerConfig{
+				Packer: struct {
+					VersionConstraints []VersionConstraint
+					RequiredPlugins    []*RequiredPlugins
+				}{
+					RequiredPlugins: []*RequiredPlugins{
+						{RequiredPlugins: map[string]*RequiredPlugin{
+							"ansible": {
+								Name:   "ansible",
+								Source: "github.com/ansible/ansible",
+								Type:   &addrs.Plugin{Hostname: "github.com", Namespace: "ansible", Type: "ansible"},
+								Requirement: VersionConstraint{
+									Required: nil,
+								},
+								PluginDependencyReason: PluginDependencyImplicit,
+							},
+						}},
+					},
+				},
+			}},
+		{"missing-required-plugin-for-post-processor", PackerConfig{
+			parser: getBasicParser(func(p *Parser) {
+				p.PluginConfig.PostProcessorRedirects = map[string]string{
+					"docker-push": "github.com/hashicorp/docker",
+				}
+			},
+			)},
+			`
+			packer {
+			}`, `
+			build {
+				post-processor "docker-push" {}
+			}
+			`,
+			false,
+			PackerConfig{
+				Packer: struct {
+					VersionConstraints []VersionConstraint
+					RequiredPlugins    []*RequiredPlugins
+				}{
+					RequiredPlugins: []*RequiredPlugins{
+						{RequiredPlugins: map[string]*RequiredPlugin{
+							"docker": {
+								Name:   "docker",
+								Source: "github.com/hashicorp/docker",
+								Type:   &addrs.Plugin{Hostname: "github.com", Namespace: "hashicorp", Type: "docker"},
+								Requirement: VersionConstraint{
+									Required: nil,
+								},
+								PluginDependencyReason: PluginDependencyImplicit,
+							},
+						}},
+					},
+				},
+			}},
+		{"missing-required-plugin-for-nested-post-processor", PackerConfig{
+			parser: getBasicParser(func(p *Parser) {
+				p.PluginConfig.PostProcessorRedirects = map[string]string{
+					"docker-push": "github.com/hashicorp/docker",
+				}
+			},
+			)},
+			`
+			packer {
+			}`, `
+			build {
+				post-processors {
+					post-processor "docker-push" {
+					}
+				}
+			}
+			`,
+			false,
+			PackerConfig{
+				Packer: struct {
+					VersionConstraints []VersionConstraint
+					RequiredPlugins    []*RequiredPlugins
+				}{
+					RequiredPlugins: []*RequiredPlugins{
+						{RequiredPlugins: map[string]*RequiredPlugin{
+							"docker": {
+								Name:   "docker",
+								Source: "github.com/hashicorp/docker",
+								Type:   &addrs.Plugin{Hostname: "github.com", Namespace: "hashicorp", Type: "docker"},
+								Requirement: VersionConstraint{
+									Required: nil,
+								},
+								PluginDependencyReason: PluginDependencyImplicit,
+							},
+						}},
+					},
+				},
+			}},
+
+		{"required-plugin-renamed", PackerConfig{
+			parser: getBasicParser(func(p *Parser) {
+				p.PluginConfig.BuilderRedirects = map[string]string{
+					"amazon-chroot": "github.com/hashicorp/amazon",
+				}
+			},
+			)},
+			`
+			packer {
+				required_plugins {
+					amazon-v1 = {
+						source  = "github.com/hashicorp/amazon"
+						version = "~> v1.0"
+					}
+				}
+			}`, `
+			source "amazon-v1-chroot" "example" {
+			}
+			source "amazon-chroot" "example" {
+			}
+			`,
+			false,
+			PackerConfig{
+				Packer: struct {
+					VersionConstraints []VersionConstraint
+					RequiredPlugins    []*RequiredPlugins
+				}{
+					RequiredPlugins: []*RequiredPlugins{
+						{RequiredPlugins: map[string]*RequiredPlugin{
+							"amazon-v1": {
+								Name:   "amazon-v1",
+								Source: "github.com/hashicorp/amazon",
+								Type:   &addrs.Plugin{Hostname: "github.com", Namespace: "hashicorp", Type: "amazon"},
+								Requirement: VersionConstraint{
+									Required: mustVersionConstraints(version.NewConstraint("~> v1.0")),
+								},
+								PluginDependencyReason: PluginDependencyExplicit,
+							},
+						}},
+						{RequiredPlugins: map[string]*RequiredPlugin{
+							"amazon": {
+								Name:   "amazon",
+								Source: "github.com/hashicorp/amazon",
+								Type:   &addrs.Plugin{Hostname: "github.com", Namespace: "hashicorp", Type: "amazon"},
+								Requirement: VersionConstraint{
+									Required: nil,
+								},
+								PluginDependencyReason: PluginDependencyImplicit,
+							},
+						}},
+					},
+				},
+			}},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			cfg := tt.cfg
+			file, diags := cfg.parser.ParseHCL([]byte(tt.requirePlugins), "required_plugins.pkr.hcl")
+			if len(diags) > 0 {
+				t.Fatal(diags)
+			}
+			if diags := cfg.decodeRequiredPluginsBlock(file); len(diags) > 0 {
+				t.Fatal(diags)
+			}
+
+			rest, diags := cfg.parser.ParseHCL([]byte(tt.restOfTemplate), "rest.pkr.hcl")
+			if len(diags) > 0 {
+				t.Fatal(diags)
+			}
+			if gotDiags := cfg.decodeImplicitRequiredPluginsBlocks(rest); (len(gotDiags) > 0) != tt.wantDiags {
+				t.Fatal(gotDiags)
+			}
+			if diff := cmp.Diff(tt.wantConfig, cfg, cmpOpts...); diff != "" {
+				t.Errorf("PackerConfig.inferImplicitRequiredPluginFromBlocks() unexpected PackerConfig: %v", diff)
+			}
+		})
+	}
+}

main.go

@@ -297,6 +297,67 @@ func loadConfig() (*config, error) {
 		PluginMinPort:      10000,
 		PluginMaxPort:      25000,
 		KnownPluginFolders: packer.PluginFolders("."),
+
+		// BuilderRedirects
+		BuilderRedirects: map[string]string{
+
+			// "amazon-chroot":       "github.com/hashicorp/amazon",
+			// "amazon-ebs":          "github.com/hashicorp/amazon",
+			// "amazon-ebssurrogate": "github.com/hashicorp/amazon",
+			// "amazon-ebsvolume":    "github.com/hashicorp/amazon",
+			// "amazon-instance":     "github.com/hashicorp/amazon",
+
+			// "azure-arm":    "github.com/hashicorp/azure",
+			// "azure-chroot": "github.com/hashicorp/azure",
+			// "dtl":          "github.com/hashicorp/azure",
+
+			// "docker": "github.com/hashicorp/docker",
+
+			// "googlecompute": "github.com/hashicorp/googlecompute",
+
+			// "parallels-iso": "github.com/hashicorp/parallels",
+			// "parallels-pvm": "github.com/hashicorp/parallels",
+
+			// "qemu": "github.com/hashicorp/qemu",
+
+			// "vagrant": "github.com/hashicorp/vagrant",
+
+			// "virtualbox-iso": "github.com/hashicorp/virtualbox",
+			// "virtualbox-ovf": "github.com/hashicorp/virtualbox",
+			// "virtualbox-vm":  "github.com/hashicorp/virtualbox",
+
+			// "vmware-iso": "github.com/hashicorp/vmware",
+			// "vmware-vmx": "github.com/hashicorp/vmware",
+
+			// "vsphere-iso":   "github.com/hashicorp/vsphere",
+			// "vsphere-clone": "github.com/hashicorp/vsphere",
+		},
+		DatasourceRedirects: map[string]string{
+			// "amazon-ami": "github.com/hashicorp/amazon",
+		},
+		ProvisionerRedirects: map[string]string{
+			// "ansible":       "github.com/hashicorp/ansible",
+			// "ansible-local": "github.com/hashicorp/ansible",
+
+			// "azure-dtlartifact": "github.com/hashicorp/azure",
+		},
+		PostProcessorRedirects: map[string]string{
+			// "amazon-import": "github.com/hashicorp/amazon",
+
+			// "docker-import": "github.com/hashicorp/docker",
+			// "docker-push":   "github.com/hashicorp/docker",
+			// "docker-save":   "github.com/hashicorp/docker",
+			// "docker-tag":    "github.com/hashicorp/docker",
+
+			// "googlecompute-export": "github.com/hashicorp/googlecompute",
+			// "googlecompute-import": "github.com/hashicorp/googlecompute",
+
+			// "vagrant":       "github.com/hashicorp/vagrant",
+			// "vagrant-cloud": "github.com/hashicorp/vagrant",
+
+			// "vsphere":          "github.com/hashicorp/vsphere",
+			// "vsphere-template": "github.com/hashicorp/vsphere",
+		},
 	}
 	if err := config.Plugins.Discover(); err != nil {
 		return nil, err

packer/plugin-getter/plugins.go

@@ -38,6 +38,9 @@ type Requirement struct {
 	// VersionConstraints as defined by user. Empty ( to be avoided ) means
 	// highest found version.
 	VersionConstraints version.Constraints
+
+	// was this require implicitly guessed ?
+	Implicit bool
 }
 
 type BinaryInstallationOptions struct {

packer/plugin.go

@@ -24,6 +24,23 @@ type PluginConfig struct {
 	Provisioners       ProvisionerSet
 	PostProcessors     PostProcessorSet
 	DataSources        DatasourceSet
+
+	// Redirects are only set when a plugin was completely moved out; they allow
+	// telling where a plugin has moved by checking if a known component of this
+	// plugin is used. For example implicitly require the
+	// github.com/hashicorp/amazon plugin if it was moved out and the
+	// "amazon-ebs" plugin is used, but not found.
+	//
+	// Redirects will be bypassed if the redirected components are already found
+	// in their corresponding sets (Builders, Provisioners, PostProcessors,
+	// DataSources). That is, for example, if you manually put a single
+	// component plugin in the plugins folder.
+	//
+	// Example BuilderRedirects: "amazon-ebs" => "github.com/hashicorp/amazon"
+	BuilderRedirects       map[string]string
+	DatasourceRedirects    map[string]string
+	ProvisionerRedirects   map[string]string
+	PostProcessorRedirects map[string]string
 }
 
 // PACKERSPACE is used to represent the spaces that separate args for a command

website/content/docs/commands/init.mdx

@@ -67,10 +67,21 @@ plugins will be installed in the [Plugin
 Directory](/docs/configure#packer-s-plugin-directory).
 
 See [Installing Plugins](/docs/plugins#installing-plugins) for more information on how plugin installation works.
+
+### Implicit required plugin
+
+This is part of a set of breaking changes made to decouple Packer releases from
+plugin releases. To make the transition easier, we will tag components of these
+plugins as "moved out". If one of the components of a moved out plugin is used
+in a config file, but there is no mention of that plugin in the
+"required_plugin" block, then Packer init will automatically download and
+install that plugin. Packer will then display a warning and suggest that you
+add the plugin to your required_plugin block. We recommend you use the
+required_plugin block even if you are only using official plugins, because it
+allows you to set the plugin version to avoid surprises in the future.
+
 ## Options
 
 - `-upgrade` - On top of installing missing plugins, update installed plugins to
   the latest available version, if there is a new higher one. Note that this
   still takes into consideration the version constraint of the config.
-
-