feat(01-02): add optional plugin services and HasPlugin

- App-scoped typed Publish/Lookup with duplicate-provider errors
- Set plugin IDs before Register so HasPlugin sees the full set
- Greeter uses pact.OptionalMessage without importing optional

backpack/app.go

@@ -1,13 +1,71 @@
 package backpack
 
-import "git.golem15.com/golem15/summercms/compass"
+import (
+	"fmt"
+	"sync"
+
+	"git.golem15.com/golem15/summercms/compass"
+)
 
 // App is the per-instance application container. It must not import party.
 type App struct {
 	Config   *compass.Config
+	Services *Registry
+
+	mu      sync.RWMutex
+	plugins map[string]struct{}
 }
 
 // New returns an App that owns cfg.
 func New(cfg *compass.Config) *App {
-	return &App{Config: cfg}
+	return &App{
+		Config:   cfg,
+		Services: NewRegistry(),
+		plugins:  make(map[string]struct{}),
+	}
+}
+
+// SetPlugins records the complete activated plugin set. HasPlugin uses this
+// list, including plugins that have not yet Booted.
+func (a *App) SetPlugins(ids []string) {
+	if a == nil {
+		return
+	}
+	next := make(map[string]struct{}, len(ids))
+	for _, id := range ids {
+		if id != "" {
+			next[id] = struct{}{}
+		}
+	}
+	a.mu.Lock()
+	a.plugins = next
+	a.mu.Unlock()
+}
+
+// HasPlugin reports whether id is in the complete registered set.
+func (a *App) HasPlugin(id string) bool {
+	if a == nil {
+		return false
+	}
+	a.mu.RLock()
+	defer a.mu.RUnlock()
+	_, ok := a.plugins[id]
+	return ok
+}
+
+// Publish stores an app-scoped service under T.
+func (a *App) Publish[T any](value T) error {
+	if a == nil || a.Services == nil {
+		return fmt.Errorf("backpack: app has no service registry")
+	}
+	return a.Services.Publish(value)
+}
+
+// Lookup returns the app-scoped service published under T.
+func (a *App) Lookup[T any]() (T, bool) {
+	var zero T
+	if a == nil || a.Services == nil {
+		return zero, false
+	}
+	return a.Services.Lookup[T]()
 }

backpack/services.go

@@ -0,0 +1,60 @@
+package backpack
+
+import (
+	"fmt"
+	"reflect"
+	"sync"
+)
+
+// Registry is an app-scoped typed service catalog. It has no process-global state.
+type Registry struct {
+	mu sync.RWMutex
+	m  map[reflect.Type]any
+}
+
+// NewRegistry returns an empty service registry.
+func NewRegistry() *Registry {
+	return &Registry{m: make(map[reflect.Type]any)}
+}
+
+// Publish stores value under the concrete type argument T. Publishing the
+// same T twice is an error.
+func (r *Registry) Publish[T any](value T) error {
+	if r == nil {
+		return fmt.Errorf("backpack: registry is nil")
+	}
+	if any(value) == nil {
+		return fmt.Errorf("backpack: publish nil service")
+	}
+	key := reflect.TypeFor[T]()
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	if r.m == nil {
+		r.m = make(map[reflect.Type]any)
+	}
+	if _, exists := r.m[key]; exists {
+		return fmt.Errorf("backpack: duplicate provider for %s", key)
+	}
+	r.m[key] = value
+	return nil
+}
+
+// Lookup returns the service published under T, or (zero, false).
+func (r *Registry) Lookup[T any]() (T, bool) {
+	var zero T
+	if r == nil {
+		return zero, false
+	}
+	key := reflect.TypeFor[T]()
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+	v, ok := r.m[key]
+	if !ok {
+		return zero, false
+	}
+	got, ok := v.(T)
+	if !ok {
+		return zero, false
+	}
+	return got, true
+}

examples/hello/go.mod

@@ -8,6 +8,7 @@ require (
 	git.golem15.com/golem15/summercms v0.0.0
 	git.golem15.com/golem15/summercms/examples/hello/plugins/base v0.0.0
 	git.golem15.com/golem15/summercms/examples/hello/plugins/greeter v0.0.0
+	git.golem15.com/golem15/summercms/examples/hello/plugins/optional v0.0.0
 )
 
 require (
@@ -32,4 +33,5 @@ replace (
 	git.golem15.com/golem15/summercms => ../..
 	git.golem15.com/golem15/summercms/examples/hello/plugins/base => ./plugins/base
 	git.golem15.com/golem15/summercms/examples/hello/plugins/greeter => ./plugins/greeter
+	git.golem15.com/golem15/summercms/examples/hello/plugins/optional => ./plugins/optional
 )

examples/hello/plugins.gen.go

@@ -5,10 +5,12 @@ package main
 import (
 	_ "git.golem15.com/golem15/summercms/examples/hello/plugins/base"
 	_ "git.golem15.com/golem15/summercms/examples/hello/plugins/greeter"
+	_ "git.golem15.com/golem15/summercms/examples/hello/plugins/optional"
 )
 
 // PluginIDs is the ordered plugin list from summer.yaml.
 var PluginIDs = []string{
 	"golem15.hello",
 	"golem15.greeter",
+	"golem15.optional",
 }

examples/hello/plugins/base/plugin.go

@@ -5,9 +5,12 @@ import (
 	"io/fs"
 
 	"git.golem15.com/golem15/summercms/backpack"
+	"git.golem15.com/golem15/summercms/pact"
 	"git.golem15.com/golem15/summercms/party"
 )
 
+var _ pact.HasConfig = (*Plugin)(nil)
+
 //go:embed config
 var configFS embed.FS
 

examples/hello/plugins/greeter/plugin.go

@@ -5,12 +5,14 @@ import (
 
 	"git.golem15.com/golem15/summercms/backpack"
 	"git.golem15.com/golem15/summercms/bonfire"
+	"git.golem15.com/golem15/summercms/pact"
 	"git.golem15.com/golem15/summercms/party"
 )
 
 // Plugin is the golem15.greeter plugin. It requires golem15.hello.
 type Plugin struct {
 	app   *backpack.App
+	extra string
 }
 
 func (p *Plugin) ID() string         { return "golem15.greeter" }
@@ -20,6 +22,12 @@ func (p *Plugin) Register(*backpack.App) error { return nil }
 
 func (p *Plugin) Boot(app *backpack.App) error {
 	p.app = app
+	p.extra = ""
+	if app != nil && app.HasPlugin("golem15.optional") {
+		if msg, ok := app.Lookup[pact.OptionalMessage](); ok {
+			p.extra = msg.Message()
+		}
+	}
 	return nil
 }
 
@@ -36,12 +44,14 @@ func (p *Plugin) Commands() []bonfire.Command {
 				posts = p.app.Config.Int("golem15.hello.posts_per_page")
 				debug = p.app.Config.Bool("app.debug")
 			}
-			out.Printf("name=%s posts_per_page=%d debug=%t\n", name, posts, debug)
+			out.Printf("name=%s posts_per_page=%d debug=%t extra=%s\n", name, posts, debug, p.extra)
 			return nil
 		},
 	}}
 }
 
+var _ pact.HasCommands = (*Plugin)(nil)
+
 func init() {
 	party.Register(&Plugin{})
 }

examples/hello/plugins/greeter/plugin_test.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"os"
 	"strings"
 	"testing"
 
@@ -61,6 +62,16 @@ func TestBootUsesPublishedOptionalService(t *testing.T) {
 	}
 }
 
+func TestGreeterSourceDoesNotImportOptional(t *testing.T) {
+	body, err := os.ReadFile("plugin.go")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if strings.Contains(string(body), "plugins/optional") {
+		t.Fatal("greeter must not import the optional plugin module")
+	}
+}
+
 func runHelloCmd(t *testing.T, p *Plugin) string {
 	t.Helper()
 	cmds := p.Commands()

examples/hello/plugins/optional/config/config.yaml

@@ -0,0 +1 @@
+enabled: true

examples/hello/plugins/optional/go.mod

@@ -0,0 +1,27 @@
+module git.golem15.com/golem15/summercms/examples/hello/plugins/optional
+
+go 1.27.0
+
+toolchain go1.27.0
+
+require git.golem15.com/golem15/summercms v0.0.0
+
+require (
+	github.com/fsnotify/fsnotify v1.9.0 // indirect
+	github.com/go-viper/mapstructure/v2 v2.4.0 // indirect
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/knadh/koanf/maps v0.1.2 // indirect
+	github.com/knadh/koanf/parsers/yaml v1.1.1 // indirect
+	github.com/knadh/koanf/providers/confmap v1.0.1 // indirect
+	github.com/knadh/koanf/providers/env/v2 v2.0.1 // indirect
+	github.com/knadh/koanf/providers/file v1.2.1 // indirect
+	github.com/knadh/koanf/v2 v2.3.6 // indirect
+	github.com/mitchellh/copystructure v1.2.0 // indirect
+	github.com/mitchellh/reflectwalk v1.0.2 // indirect
+	github.com/spf13/cobra v1.10.2 // indirect
+	github.com/spf13/pflag v1.0.9 // indirect
+	go.yaml.in/yaml/v3 v3.0.4 // indirect
+	golang.org/x/sys v0.32.0 // indirect
+)
+
+replace git.golem15.com/golem15/summercms => ../../../..

examples/hello/plugins/optional/go.sum

@@ -0,0 +1,47 @@
+github.com/cpuguy83/go-md2man/v2 v2.0.6/go.mod h1:oOW0eioCTA6cOiMLiUPZOpcVxMig6NIQQ7OS05n1F4g=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/fsnotify/fsnotify v1.9.0 h1:2Ml+OJNzbYCTzsxtv8vKSFD9PbJjmhYF14k/jKC7S9k=
+github.com/fsnotify/fsnotify v1.9.0/go.mod h1:8jBTzvmWwFyi3Pb8djgCCO5IBqzKJ/Jwo8TRcHyHii0=
+github.com/go-viper/mapstructure/v2 v2.4.0 h1:EBsztssimR/CONLSZZ04E8qAkxNYq4Qp9LvH92wZUgs=
+github.com/go-viper/mapstructure/v2 v2.4.0/go.mod h1:oJDH3BJKyqBA2TXFhDsKDGDTlndYOZ6rGS0BRZIxGhM=
+github.com/inconshreveable/mousetrap v1.1.0 h1:wN+x4NVGpMsO7ErUn/mUI3vEoE6Jt13X2s0bqwp9tc8=
+github.com/inconshreveable/mousetrap v1.1.0/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
+github.com/knadh/koanf/maps v0.1.2 h1:RBfmAW5CnZT+PJ1CVc1QSJKf4Xu9kxfQgYVQSu8hpbo=
+github.com/knadh/koanf/maps v0.1.2/go.mod h1:npD/QZY3V6ghQDdcQzl1W4ICNVTkohC8E73eI2xW4yI=
+github.com/knadh/koanf/parsers/yaml v1.1.1 h1:u70vV5IyaM0HvONh8HoqBC97oTgO33KcpZbTLiKVinU=
+github.com/knadh/koanf/parsers/yaml v1.1.1/go.mod h1:HHmcHXUrp9cOPcuC+2wrr44GTUB0EC+PyfN3HZD9tFg=
+github.com/knadh/koanf/providers/confmap v1.0.1 h1:L15hbvMqlvhwUuCtL9BkL+rqiMAjk6cZc8O9XoDtE3A=
+github.com/knadh/koanf/providers/confmap v1.0.1/go.mod h1:txHYHiI2hAtF0/0sCmcuol4IDcuQbKTybiB1nOcUo1A=
+github.com/knadh/koanf/providers/env/v2 v2.0.1 h1:a3KagndPqhcWHQv6Pz4OZmwkI/yMeTjkiZye6ZCkyW0=
+github.com/knadh/koanf/providers/env/v2 v2.0.1/go.mod h1:1g01PE+Ve1gBfWNNw2wmULRP0tc8RJrjn5p2N/jNCIc=
+github.com/knadh/koanf/providers/file v1.2.1 h1:bEWbtQwYrA+W2DtdBrQWyXqJaJSG3KrP3AESOJYp9wM=
+github.com/knadh/koanf/providers/file v1.2.1/go.mod h1:bp1PM5f83Q+TOUu10J/0ApLBd9uIzg+n9UgthfY+nRA=
+github.com/knadh/koanf/v2 v2.3.6 h1:JoQPSJmvS4aP0xNc8xMDr5tcrkSEInL23/Il7pITAKo=
+github.com/knadh/koanf/v2 v2.3.6/go.mod h1:gRb40VRAbd4iJMYYD5IxZ6hfuopFcXBpc9bbQpZwo28=
+github.com/kr/pretty v0.2.1 h1:Fmg33tUaq4/8ym9TJN1x7sLJnHVwhP33CNkpYV/7rwI=
+github.com/kr/pretty v0.2.1/go.mod h1:ipq/a2n7PKx3OHsz4KJII5eveXtPO4qwEXGdVfWzfnI=
+github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
+github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
+github.com/mitchellh/copystructure v1.2.0 h1:vpKXTN4ewci03Vljg/q9QvCGUDttBOGBIa15WveJJGw=
+github.com/mitchellh/copystructure v1.2.0/go.mod h1:qLl+cE2AmVv+CoeAwDPye/v+N2HKCj9FbZEVFJRxO9s=
+github.com/mitchellh/reflectwalk v1.0.2 h1:G2LzWKi524PWgd3mLHV8Y5k7s6XUvT0Gef6zxSIeXaQ=
+github.com/mitchellh/reflectwalk v1.0.2/go.mod h1:mSTlrgnPZtwu0c4WaC2kGObEpuNDbx0jmZXqmk4esnw=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
+github.com/spf13/cobra v1.10.2 h1:DMTTonx5m65Ic0GOoRY2c16WCbHxOOw6xxezuLaBpcU=
+github.com/spf13/cobra v1.10.2/go.mod h1:7C1pvHqHw5A4vrJfjNwvOdzYu0Gml16OCs2GRiTUUS4=
+github.com/spf13/pflag v1.0.9 h1:9exaQaMOCwffKiiiYk6/BndUBv+iRViNW+4lEMi0PvY=
+github.com/spf13/pflag v1.0.9/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
+github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=
+github.com/stretchr/testify v1.8.4/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXlSw2iwfAo=
+go.yaml.in/yaml/v3 v3.0.4 h1:tfq32ie2Jv2UxXFdLJdh3jXuOzWiL1fo0bu/FbuKpbc=
+go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
+golang.org/x/sys v0.32.0 h1:s77OFDvIQeibCmezSnk/q6iAfkdiQaJi4VzroCFrN20=
+golang.org/x/sys v0.32.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 h1:YR8cESwS4TdDjEe65xsg0ogRM/Nc3DYOhEAlW+xobZo=
+gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

examples/hello/plugins/optional/plugin.go

@@ -0,0 +1,43 @@
+package optional
+
+import (
+	"embed"
+	"io/fs"
+
+	"git.golem15.com/golem15/summercms/backpack"
+	"git.golem15.com/golem15/summercms/pact"
+	"git.golem15.com/golem15/summercms/party"
+)
+
+//go:embed config
+var configFS embed.FS
+
+// Plugin is the golem15.optional plugin. Greeter may use it without importing this package.
+type Plugin struct{}
+
+func (p *Plugin) ID() string         { return "golem15.optional" }
+func (p *Plugin) Requires() []string { return nil }
+
+func (p *Plugin) Register(app *backpack.App) error {
+	if app == nil {
+		return nil
+	}
+	return app.Publish[pact.OptionalMessage](extra{})
+}
+
+func (p *Plugin) Boot(*backpack.App) error { return nil }
+
+func (p *Plugin) ConfigFS() fs.FS { return configFS }
+
+type extra struct{}
+
+func (extra) Message() string { return "hello-from-optional" }
+
+var (
+	_ pact.HasConfig       = (*Plugin)(nil)
+	_ pact.OptionalMessage = extra{}
+)
+
+func init() {
+	party.Register(&Plugin{})
+}

examples/hello/summer.yaml

@@ -5,3 +5,5 @@ plugins:
     module: git.golem15.com/golem15/summercms/examples/hello/plugins/base
   - id: golem15.greeter
     module: git.golem15.com/golem15/summercms/examples/hello/plugins/greeter
+  - id: golem15.optional
+    module: git.golem15.com/golem15/summercms/examples/hello/plugins/optional

go.work

@@ -7,4 +7,5 @@ use (
 	./examples/hello
 	./examples/hello/plugins/base
 	./examples/hello/plugins/greeter
+	./examples/hello/plugins/optional
 )

internal/build/build_test.go

@@ -16,7 +16,7 @@ func TestLoadHelloManifest(t *testing.T) {
 	if m.Binary != "hello" {
 		t.Fatalf("binary = %q", m.Binary)
 	}
-	if len(m.Plugins) != 2 || m.Plugins[0].ID != "golem15.hello" || m.Plugins[1].ID != "golem15.greeter" {
+	if len(m.Plugins) != 3 || m.Plugins[0].ID != "golem15.hello" || m.Plugins[1].ID != "golem15.greeter" || m.Plugins[2].ID != "golem15.optional" {
 		t.Fatalf("plugins = %+v", m.Plugins)
 	}
 }

pact/capabilities.go

@@ -18,7 +18,16 @@ type HasConfig interface {
 	ConfigFS() fs.FS
 }
 
-// Reserved KERN-03 capability names, declared when their first consumers exist:
+// OptionalMessage is a service an optional plugin may publish so other
+// plugins can integrate without importing that plugin's package.
+type OptionalMessage interface {
+	Message() string
+}
+
+// Future KERN-03 capability families are type-asserted when their first
+// consumer packages exist. Method payloads are not declared here so pact
+// does not import surf, lagoon, festival, or other packages that Phase 1
+// does not yet ship:
 //
 //	HasModels
 //	HasMigrations
@@ -32,3 +41,6 @@ type HasConfig interface {
 //	HasSchedule
 //	HasMailTemplates
 //	HasLang
+//
+// Phase 1 type-asserts only HasConfig (party, before Register) and
+// HasCommands (generated app main, after Boot).

party/registry.go

@@ -98,6 +98,12 @@ func activate(registered []Plugin, app *backpack.App, ids []string) ([]Plugin, e
 		return nil, err
 	}
 
+	orderedIDs := make([]string, len(ordered))
+	for i, p := range ordered {
+		orderedIDs[i] = p.ID()
+	}
+	app.SetPlugins(orderedIDs)
+
 	for _, p := range ordered {
 		if hc, ok := p.(pact.HasConfig); ok && app.Config != nil {
 			if err := app.Config.MergePlugin(p.ID(), hc.ConfigFS()); err != nil {