Add instance command registry and composition

app.go

@@ -0,0 +1,41 @@
+package commandkit
+
+import "fmt"
+
+// App owns one command registry and its application identity.
+type App struct {
+	identity Identity
+	commands map[string]*commandNode
+}
+
+type commandNode struct {
+	command  Command
+	reserved bool
+}
+
+// New creates an application with the supplied identity and initial commands.
+// The identity name must not be empty. The root help and version names are
+// reserved for generated commands.
+func New(identity Identity, commands ...Command) (*App, error) {
+	if identity.Name == "" {
+		return nil, fmt.Errorf("application identity name must not be empty")
+	}
+
+	app := &App{
+		identity: identity,
+		commands: map[string]*commandNode{
+			"help": {
+				command:  Command{name: "help", summary: "Show help for commands."},
+				reserved: true,
+			},
+			"version": {
+				command:  Command{name: "version", summary: "Show application version."},
+				reserved: true,
+			},
+		},
+	}
+	if err := app.Register(commands...); err != nil {
+		return nil, err
+	}
+	return app, nil
+}

command.go

@@ -0,0 +1,265 @@
+package commandkit
+
+import (
+	"fmt"
+	"strings"
+)
+
+// Command is an opaque command declaration. Use NewCommand or Group to create
+// declarations and WithChildren to compose them.
+type Command struct {
+	name        string
+	summary     string
+	description string
+	children    []Command
+	payload     commandPayload
+}
+
+// Supplied carries a value and whether it was explicitly provided.
+type Supplied[T any] struct {
+	// Value is the associated value.
+	Value T
+	// Set reports whether a caller explicitly supplied the value.
+	Set bool
+}
+
+// FlagMeta describes a command flag.
+type FlagMeta struct {
+	// Name is the flag name without leading dashes.
+	Name string
+	// Short is an optional one-byte spelling.
+	Short string
+	// Usage briefly describes the flag.
+	Usage string
+	// Required reports whether execution requires the flag to be supplied.
+	Required bool
+}
+
+// ArgumentMeta describes a positional command argument.
+type ArgumentMeta struct {
+	// Name is the argument name shown in command help.
+	Name string
+	// Usage briefly describes the argument.
+	Usage string
+}
+
+// Flag represents a typed binding for a command flag.
+type Flag[I any] struct {
+	binding flagBinding[I]
+}
+
+type flagBinding[I any] struct {
+	meta    FlagMeta
+	prepare func([]string) (func(*I), error)
+	valid   bool
+}
+
+// Argument represents a typed binding for a positional command argument.
+type Argument[I any] struct {
+	binding argumentBinding[I]
+}
+
+type argumentBinding[I any] struct {
+	meta    ArgumentMeta
+	min     int
+	max     int
+	prepare func([]string) (func(*I), error)
+	valid   bool
+}
+
+// CommandSpec declares one command using typed input and handler callbacks.
+type CommandSpec[I any] struct {
+	// Name is one command path component.
+	Name string
+	// Summary is a short description of the command.
+	Summary string
+	// Description provides additional command detail.
+	Description string
+	// NewInput creates an input value for execution. A nil factory uses a fresh
+	// zero value.
+	NewInput func() I
+	// Flags declares the command's local flags.
+	Flags []Flag[I]
+	// Arguments declares the command's positional inputs.
+	Arguments []Argument[I]
+	// CheckInput validates declared combinations of parsed inputs.
+	CheckInput func(I) error
+	// Run handles an invocation. It may be nil for a command used as a group.
+	Run func(Invocation, I) Outcome
+}
+
+type commandPayload interface {
+	validate() error
+	hasRun() bool
+	newInput() any
+	run(Invocation, any) Outcome
+}
+
+type typedCommand[I any] struct {
+	spec CommandSpec[I]
+}
+
+func (c typedCommand[I]) validate() error {
+	return validateBindings(c.spec.Flags, c.spec.Arguments)
+}
+
+func (c typedCommand[I]) hasRun() bool {
+	return c.spec.Run != nil
+}
+
+func (c typedCommand[I]) newInput() any {
+	var input I
+	if c.spec.NewInput != nil {
+		input = c.spec.NewInput()
+	}
+	return &input
+}
+
+func (c typedCommand[I]) run(invocation Invocation, input any) Outcome {
+	return c.spec.Run(invocation, *input.(*I))
+}
+
+// NewCommand validates and creates a typed command declaration. It retains
+// callbacks without invoking them and copies the declarative flag and argument
+// slices.
+func NewCommand[I any](spec CommandSpec[I]) (Command, error) {
+	if err := validateCommandName(spec.Name); err != nil {
+		return Command{}, err
+	}
+	copySpec := spec
+	copySpec.Flags = append([]Flag[I](nil), spec.Flags...)
+	copySpec.Arguments = append([]Argument[I](nil), spec.Arguments...)
+	payload := typedCommand[I]{spec: copySpec}
+	if err := payload.validate(); err != nil {
+		return Command{}, fmt.Errorf("command %q: %w", spec.Name, err)
+	}
+	return Command{
+		name:        spec.Name,
+		summary:     spec.Summary,
+		description: spec.Description,
+		payload:     payload,
+	}, nil
+}
+
+// Group creates a non-runnable command group with the supplied children.
+func Group(name, summary string, children ...Command) (Command, error) {
+	if err := validateCommandName(name); err != nil {
+		return Command{}, err
+	}
+	group := Command{name: name, summary: summary, children: cloneCommands(children)}
+	if err := validateCommandDeclaration(group); err != nil {
+		return Command{}, err
+	}
+	return group, nil
+}
+
+// WithChildren returns a copy of parent with the supplied relative child
+// declarations. The parent's optional handler and input bindings are retained.
+func WithChildren(parent Command, children ...Command) (Command, error) {
+	if err := validateCommandDeclaration(parent); err != nil {
+		return Command{}, fmt.Errorf("parent command: %w", err)
+	}
+	combined := make([]Command, 0, len(parent.children)+len(children))
+	combined = append(combined, parent.children...)
+	combined = append(combined, children...)
+	result := parent
+	result.children = cloneCommands(combined)
+	if err := validateCommandDeclaration(result); err != nil {
+		return Command{}, err
+	}
+	return result, nil
+}
+
+func cloneCommands(commands []Command) []Command {
+	if len(commands) == 0 {
+		return nil
+	}
+	cloned := make([]Command, len(commands))
+	for i, command := range commands {
+		cloned[i] = cloneCommand(command)
+	}
+	return cloned
+}
+
+func cloneCommand(command Command) Command {
+	command.children = cloneCommands(command.children)
+	return command
+}
+
+func validateCommandDeclaration(command Command) error {
+	if err := validateCommandName(command.name); err != nil {
+		return err
+	}
+	if command.payload != nil {
+		if err := command.payload.validate(); err != nil {
+			return fmt.Errorf("command %q: %w", command.name, err)
+		}
+	}
+
+	children := make(map[string]struct{}, len(command.children))
+	for _, child := range command.children {
+		if err := validateCommandDeclaration(child); err != nil {
+			return err
+		}
+		if _, exists := children[child.name]; exists {
+			return fmt.Errorf("duplicate child command %q under %q", child.name, command.name)
+		}
+		children[child.name] = struct{}{}
+	}
+	return nil
+}
+
+func validateCommandName(name string) error {
+	fields := strings.Fields(name)
+	if len(fields) != 1 || fields[0] != name || strings.HasPrefix(name, "-") || name == "--" {
+		return fmt.Errorf("command name %q must be one non-option token", name)
+	}
+	return nil
+}
+
+func validateBindings[I any](flags []Flag[I], arguments []Argument[I]) error {
+	flagNames := make(map[string]struct{}, len(flags))
+	shortNames := make(map[string]struct{}, len(flags))
+	for _, flag := range flags {
+		binding := flag.binding
+		if binding.meta.Name == "" || strings.ContainsAny(binding.meta.Name, " \t\r\n") || strings.HasPrefix(binding.meta.Name, "-") {
+			return fmt.Errorf("flag name %q must be a nonempty token without leading dashes", binding.meta.Name)
+		}
+		if binding.meta.Name == "help" {
+			return fmt.Errorf("flag name %q is reserved for help", binding.meta.Name)
+		}
+		if _, exists := flagNames[binding.meta.Name]; exists {
+			return fmt.Errorf("duplicate flag name %q", binding.meta.Name)
+		}
+		flagNames[binding.meta.Name] = struct{}{}
+		if binding.meta.Short != "" {
+			if len(binding.meta.Short) != 1 || binding.meta.Short == "-" {
+				return fmt.Errorf("short spelling %q must be one byte", binding.meta.Short)
+			}
+			if binding.meta.Short == "h" {
+				return fmt.Errorf("short spelling %q is reserved for help", binding.meta.Short)
+			}
+			if _, exists := shortNames[binding.meta.Short]; exists {
+				return fmt.Errorf("duplicate short spelling %q", binding.meta.Short)
+			}
+			shortNames[binding.meta.Short] = struct{}{}
+		}
+		if !binding.valid || binding.prepare == nil {
+			return fmt.Errorf("flag %q is missing parser or setter wiring", binding.meta.Name)
+		}
+	}
+
+	for _, argument := range arguments {
+		binding := argument.binding
+		if binding.meta.Name == "" {
+			return fmt.Errorf("argument name must not be empty")
+		}
+		if binding.min < 0 || binding.max < -1 || (binding.max >= 0 && binding.min > binding.max) {
+			return fmt.Errorf("argument %q has invalid bounds %d..%d", binding.meta.Name, binding.min, binding.max)
+		}
+		if !binding.valid || binding.prepare == nil {
+			return fmt.Errorf("argument %q is missing parser or setter wiring", binding.meta.Name)
+		}
+	}
+	return nil
+}

docs/development.md

@@ -1,9 +1,9 @@
 # Developing CommandKit
 
 CommandKit currently contains adopted repository policies, accepted architectural
-decisions, implementation plans, and initial Go identity and outcome primitives.
-Command dispatch is not implemented yet. The [README](../README.md) provides
-project orientation; the
+decisions, implementation plans, identity and outcome primitives, typed command
+declarations, and an instance-owned registry. Command execution is not implemented
+yet. The [README](../README.md) provides project orientation; the
 [documentation policy](policy/documentation.md#canonical-ownership) assigns
 canonical documentation owners.
 

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # Initial CommandKit implementation plan
 
-Status: implementation underway; Stage 1 complete and Stages 2-14 pending.
+Status: implementation underway; Stages 1-2 complete and Stages 3-14 pending.
 
 Date: 2026-10-07.
 
@@ -169,7 +169,7 @@ Verified with `go test ./...`, `go mod verify`, and
 
 ## Stage 2: implement the instance registry and command declarations
 
-**Status:** pending. **Prerequisite:** Stage 1.
+**Status:** complete. **Prerequisite:** Stage 1.
 
 Implement `App`, opaque `Command`, metadata, group composition, and registration
 in root files such as `app.go`, `command.go`, and `registry.go`.
@@ -234,6 +234,9 @@ package or exported bridge methods.
 registries; duplicate nested paths; runnable-parent composition; registration errors
 leave the previous inventory intact. Execution remains Stage 5 work.
 
+**Completion:** added typed command declarations, group composition, root help and
+version reservations, and atomic per-App registration. Verified with `go test ./...`.
+
 ## Stage 3: implement typed bindings and input assembly
 
 **Status:** pending. **Prerequisite:** Stage 2.

registry.go

@@ -0,0 +1,27 @@
+package commandkit
+
+import "fmt"
+
+// Register adds a batch of root commands to the application. The batch is
+// validated before the registry is changed.
+func (a *App) Register(commands ...Command) error {
+	if a == nil {
+		return fmt.Errorf("cannot register commands on a nil app")
+	}
+
+	updated := make(map[string]*commandNode, len(a.commands)+len(commands))
+	for name, node := range a.commands {
+		updated[name] = node
+	}
+	for _, command := range commands {
+		if err := validateCommandDeclaration(command); err != nil {
+			return err
+		}
+		if _, exists := updated[command.name]; exists {
+			return fmt.Errorf("command path %q is already registered", command.name)
+		}
+		updated[command.name] = &commandNode{command: cloneCommand(command)}
+	}
+	a.commands = updated
+	return nil
+}

registry_test.go

@@ -0,0 +1,223 @@
+package commandkit
+
+import (
+	"testing"
+)
+
+type registryInput struct {
+	value string
+}
+
+func TestNewAndRegisterRetainCallbacksWithoutCallingThem(t *testing.T) {
+	var factoryCalls, prepareCalls, setterCalls, checkCalls, runCalls int
+	flag := Flag[registryInput]{binding: flagBinding[registryInput]{
+		meta:  FlagMeta{Name: "mode"},
+		valid: true,
+		prepare: func([]string) (func(*registryInput), error) {
+			prepareCalls++
+			return func(*registryInput) { setterCalls++ }, nil
+		},
+	}}
+	command, err := NewCommand(CommandSpec[registryInput]{
+		Name: "Inspect",
+		NewInput: func() registryInput {
+			factoryCalls++
+			return registryInput{}
+		},
+		Flags: []Flag[registryInput]{flag},
+		CheckInput: func(registryInput) error {
+			checkCalls++
+			return nil
+		},
+		Run: func(Invocation, registryInput) Outcome {
+			runCalls++
+			return Success()
+		},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	group, err := Group("Tools", "tools", command)
+	if err != nil {
+		t.Fatal(err)
+	}
+	app, err := New(Identity{Name: "Example"}, group)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := app.Register(); err != nil {
+		t.Fatal(err)
+	}
+
+	if factoryCalls+prepareCalls+setterCalls+checkCalls+runCalls != 0 {
+		t.Fatalf("construction invoked a callback: factory=%d prepare=%d setter=%d check=%d run=%d", factoryCalls, prepareCalls, setterCalls, checkCalls, runCalls)
+	}
+	if !app.commands["Tools"].command.children[0].payload.hasRun() {
+		t.Fatal("registered command lost its handler")
+	}
+}
+
+func TestAppsHaveIndependentRegistries(t *testing.T) {
+	first, err := New(Identity{Name: "First"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	second, err := New(Identity{Name: "Second"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	command, err := NewCommand(CommandSpec[struct{}]{Name: "custom"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := first.Register(command); err != nil {
+		t.Fatal(err)
+	}
+	if _, exists := second.commands["custom"]; exists {
+		t.Fatal("registration leaked to another app")
+	}
+	if !first.commands["help"].reserved || !first.commands["version"].reserved {
+		t.Fatal("New did not reserve generated root commands")
+	}
+}
+
+func TestCommandAndGroupNames(t *testing.T) {
+	for _, name := range []string{"", "--", "-option", "two words", " leading", "trailing "} {
+		if _, err := NewCommand(CommandSpec[struct{}]{Name: name}); err == nil {
+			t.Errorf("NewCommand accepted invalid name %q", name)
+		}
+	}
+	if _, err := NewCommand(CommandSpec[struct{}]{Name: "CamelCase"}); err != nil {
+		t.Fatalf("NewCommand rejected a custom mixed-case name: %v", err)
+	}
+
+	first, err := NewCommand(CommandSpec[struct{}]{Name: "repeat"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	second, err := NewCommand(CommandSpec[struct{}]{Name: "repeat"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := Group("parent", "", first, second); err == nil {
+		t.Fatal("Group accepted duplicate sibling paths")
+	}
+	if _, err := Group("parent", "", Command{}); err == nil {
+		t.Fatal("Group accepted an invalid child declaration")
+	}
+}
+
+func TestWithChildrenRetainsRunnableParent(t *testing.T) {
+	parent, err := NewCommand(CommandSpec[struct{}]{Name: "parent", Run: func(Invocation, struct{}) Outcome {
+		return Success()
+	}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	child, err := NewCommand(CommandSpec[struct{}]{Name: "child"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	composed, err := WithChildren(parent, child)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if composed.payload == nil || !composed.payload.hasRun() {
+		t.Fatal("WithChildren did not retain the runnable parent")
+	}
+	if len(composed.children) != 1 || composed.children[0].name != "child" {
+		t.Fatalf("children = %#v, want relative child declaration", composed.children)
+	}
+	if len(parent.children) != 0 {
+		t.Fatal("WithChildren changed the original parent declaration")
+	}
+}
+
+func TestRegisterBatchIsAtomicAndRejectsReservedPaths(t *testing.T) {
+	app, err := New(Identity{Name: "Example"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	existing, err := NewCommand(CommandSpec[struct{}]{Name: "existing"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := app.Register(existing); err != nil {
+		t.Fatal(err)
+	}
+	before := app.commands["existing"]
+	added, err := NewCommand(CommandSpec[struct{}]{Name: "added"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := app.Register(added, existing); err == nil {
+		t.Fatal("Register accepted a duplicate path")
+	}
+	if app.commands["existing"] != before {
+		t.Fatal("failed batch changed an existing registration")
+	}
+	if _, exists := app.commands["added"]; exists {
+		t.Fatal("failed batch attached a partial registration")
+	}
+	for _, name := range []string{"help", "version"} {
+		reserved, err := NewCommand(CommandSpec[struct{}]{Name: name})
+		if err != nil {
+			t.Fatal(err)
+		}
+		if err := app.Register(reserved); err == nil {
+			t.Errorf("Register replaced reserved command %q", name)
+		}
+	}
+}
+
+func TestNewRejectsEmptyIdentityAndInvalidBindingMetadata(t *testing.T) {
+	if _, err := New(Identity{}); err == nil {
+		t.Fatal("New accepted an empty identity name")
+	}
+
+	validFlag := func(name, short string) Flag[registryInput] {
+		return Flag[registryInput]{binding: flagBinding[registryInput]{
+			meta:    FlagMeta{Name: name, Short: short},
+			valid:   true,
+			prepare: func([]string) (func(*registryInput), error) { return func(*registryInput) {}, nil },
+		}}
+	}
+	for _, flags := range [][]Flag[registryInput]{
+		{validFlag("one", "x"), validFlag("one", "y")},
+		{validFlag("one", "x"), validFlag("two", "x")},
+		{validFlag("help", "")},
+		{{binding: flagBinding[registryInput]{meta: FlagMeta{Name: "missing"}}}},
+	} {
+		if _, err := NewCommand(CommandSpec[registryInput]{Name: "flags", Flags: flags}); err == nil {
+			t.Errorf("NewCommand accepted invalid flag metadata: %#v", flags)
+		}
+	}
+
+	badArgument := Argument[registryInput]{binding: argumentBinding[registryInput]{
+		meta:    ArgumentMeta{Name: "item"},
+		min:     2,
+		max:     1,
+		valid:   true,
+		prepare: func([]string) (func(*registryInput), error) { return func(*registryInput) {}, nil },
+	}}
+	if _, err := NewCommand(CommandSpec[registryInput]{Name: "args", Arguments: []Argument[registryInput]{badArgument}}); err == nil {
+		t.Fatal("NewCommand accepted invalid argument bounds")
+	}
+}
+
+func TestNewCommandCopiesBindingMetadata(t *testing.T) {
+	flags := []Flag[registryInput]{{binding: flagBinding[registryInput]{
+		meta:    FlagMeta{Name: "mode"},
+		valid:   true,
+		prepare: func([]string) (func(*registryInput), error) { return func(*registryInput) {}, nil },
+	}}}
+	command, err := NewCommand(CommandSpec[registryInput]{Name: "run", Flags: flags})
+	if err != nil {
+		t.Fatal(err)
+	}
+	flags[0].binding.meta.Name = "changed"
+	payload := command.payload.(typedCommand[registryInput])
+	if got := payload.spec.Flags[0].binding.meta.Name; got != "mode" {
+		t.Fatalf("stored flag name = %q, want %q", got, "mode")
+	}
+}