Bot: Added automatic Intents detection from handlers

This commit adds automatic Intents detection into package bot. When the
Start function is used, the intents will be OR'd after running the
options callback.

This commit also breaks the old "AddIntent" methods to rename them to
"AddIntents" for correctness.

bot/command.go

@@ -2,8 +2,24 @@ package bot
 
 import (
 	"reflect"
+
+	"github.com/diamondburned/arikawa/v2/gateway"
 )
 
+// eventIntents maps event pointer types to intents.
+var eventIntents = map[reflect.Type]gateway.Intents{}
+
+func init() {
+	for event, intent := range gateway.EventIntents {
+		fn, ok := gateway.EventCreator[event]
+		if !ok {
+			continue
+		}
+
+		eventIntents[reflect.TypeOf(fn())] = intent
+	}
+}
+
 type command struct {
 	value       reflect.Value // Func
 	event       reflect.Type
@@ -26,6 +42,15 @@ func (c *command) call(arg0 interface{}, argv ...reflect.Value) (interface{}, er
 	return callWith(c.value, arg0, argv...)
 }
 
+// intents returns the command's intents from the event.
+func (c *command) intents() gateway.Intents {
+	intents, ok := eventIntents[c.event]
+	if !ok {
+		return 0
+	}
+	return intents
+}
+
 func callWith(caller reflect.Value, arg0 interface{}, argv ...reflect.Value) (interface{}, error) {
 	var callargs = make([]reflect.Value, 0, 1+len(argv))
 

bot/ctx.go

@@ -165,6 +165,8 @@ func Start(
 		}
 	}
 
+	s.Gateway.AddIntents(c.DeriveIntents())
+
 	cancel := c.Start()
 
 	if err := s.Open(); err != nil {
@@ -229,10 +231,10 @@ func New(s *state.State, cmd interface{}) (*Context, error) {
 	return ctx, nil
 }
 
-// AddIntent adds the given Gateway Intent into the Gateway. This is a
+// AddIntents adds the given Gateway Intent into the Gateway. This is a
 // convenient function that calls Gateway's AddIntent.
-func (ctx *Context) AddIntent(i gateway.Intents) {
-	ctx.Gateway.AddIntent(i)
+func (ctx *Context) AddIntents(i gateway.Intents) {
+	ctx.Gateway.AddIntents(i)
 }
 
 // Subcommands returns the slice of subcommands. To add subcommands, use
@@ -444,3 +446,13 @@ func IndentLines(input string) string {
 	}
 	return strings.Join(lines, "\n")
 }
+
+// DeriveIntents derives all possible gateway intents from this context and all
+// its subcommands' method handlers and middlewares.
+func (ctx *Context) DeriveIntents() gateway.Intents {
+	var intents = ctx.Subcommand.DeriveIntents()
+	for _, subcmd := range ctx.subcommands {
+		intents |= subcmd.DeriveIntents()
+	}
+	return intents
+}

bot/ctx_test.go

@@ -149,6 +149,21 @@ func TestContext(t *testing.T) {
 		}
 	})
 
+	t.Run("derive intents", func(t *testing.T) {
+		intents := ctx.DeriveIntents()
+
+		assertIntents := func(target gateway.Intents, name string) {
+			if !intents.Has(target) {
+				t.Error("Derived intents do not have", name)
+			}
+		}
+
+		assertIntents(gateway.IntentGuildMessages, "guild messages")
+		assertIntents(gateway.IntentDirectMessages, "direct messages")
+		assertIntents(gateway.IntentGuildMessageTyping, "guild typing")
+		assertIntents(gateway.IntentDirectMessageTyping, "direct message typing")
+	})
+
 	t.Run("typing event", func(t *testing.T) {
 		typing := &gateway.TypingStartEvent{}
 

bot/subcommand.go

@@ -143,6 +143,10 @@ func (sub *Subcommand) NeedsName() {
 	sub.Command = lowerFirstLetter(sub.StructName)
 }
 
+func lowerFirstLetter(name string) string {
+	return strings.ToLower(string(name[0])) + name[1:]
+}
+
 // FindCommand finds the MethodContext. It panics if methodName is not found.
 func (sub *Subcommand) FindCommand(methodName string) *MethodContext {
 	for _, c := range sub.Commands {
@@ -413,6 +417,23 @@ func (sub *Subcommand) AddAliases(commandName string, aliases ...string) {
 	command.Aliases = append(command.Aliases, aliases...)
 }
 
-func lowerFirstLetter(name string) string {
-	return strings.ToLower(string(name[0])) + name[1:]
+// DeriveIntents derives all possible gateway intents from the method handlers
+// and middlewares.
+func (sub *Subcommand) DeriveIntents() gateway.Intents {
+	var intents gateway.Intents
+
+	for _, event := range sub.Events {
+		intents |= event.intents()
+	}
+	for _, command := range sub.Commands {
+		intents |= command.intents()
+	}
+	if sub.plumbed != nil {
+		intents |= sub.plumbed.intents()
+	}
+	for _, middleware := range sub.globalmws {
+		intents |= middleware.intents()
+	}
+
+	return intents
 }

gateway/gateway.go

@@ -114,7 +114,7 @@ func NewGatewayWithIntents(token string, intents ...Intents) (*Gateway, error) {
 	}
 
 	for _, intent := range intents {
-		g.AddIntent(intent)
+		g.AddIntents(intent)
 	}
 
 	return g, nil
@@ -154,9 +154,9 @@ func NewCustomGateway(gatewayURL, token string) *Gateway {
 	}
 }
 
-// AddIntent adds a Gateway Intent before connecting to the Gateway. As
-// such, this function will only work before Open() is called.
-func (g *Gateway) AddIntent(i Intents) {
+// AddIntents adds a Gateway Intent before connecting to the Gateway. As such,
+// this function will only work before Open() is called.
+func (g *Gateway) AddIntents(i Intents) {
 	g.Identifier.Intents |= i
 }
 

gateway/intents.go

@@ -1,5 +1,7 @@
 package gateway
 
+import "github.com/diamondburned/arikawa/v2/discord"
+
 // Intents for the new Discord API feature, documented at
 // https://discordapp.com/developers/docs/topics/gateway#gateway-intents.
 type Intents uint32
@@ -28,3 +30,15 @@ var PrivilegedIntents = []Intents{
 	IntentGuildPresences,
 	IntentGuildMembers,
 }
+
+// Has returns true if i has the given intents.
+func (i Intents) Has(intents Intents) bool {
+	return discord.HasFlag(uint64(i), uint64(intents))
+}
+
+// IsPrivileged returns true for each of the boolean that indicates the type of
+// the privilege.
+func (i Intents) IsPrivileged() (presences, member bool) {
+	// Keep this in sync with PrivilegedIntents.
+	return i.Has(IntentGuildPresences), i.Has(IntentGuildMembers)
+}