Implement basic tab completion support

Tab completion currently only works on commands. Contextual completion
will be added in the future.

11 files changed, 128 insertions, 36 deletions

diff --git a/commands/account/account.go b/commands/account/account.go
index c590c8ae..9c900872 100644
--- a/commands/account/account.go
+++ b/commands/account/account.go
@@ -8,9 +8,9 @@ var (
 	AccountCommands *commands.Commands
 )
 
-func register(name string, cmd commands.AercCommand) {
+func register(cmd commands.Command) {
 	if AccountCommands == nil {
 		AccountCommands = commands.NewCommands()
 	}
-	AccountCommands.Register(name, cmd)
+	AccountCommands.Register(cmd)
 }
diff --git a/commands/account/cf.go b/commands/account/cf.go
index 2816473a..197e956e 100644
--- a/commands/account/cf.go
+++ b/commands/account/cf.go
@@ -10,12 +10,22 @@ var (
 	history map[string]string
 )
 
+type ChangeFolder struct{}
+
 func init() {
 	history = make(map[string]string)
-	register("cf", ChangeFolder)
+	register(ChangeFolder{})
+}
+
+func (_ ChangeFolder) Aliases() []string {
+	return []string{"cf"}
+}
+
+func (_ ChangeFolder) Complete(aerc *widgets.Aerc, args []string) []string {
+	return nil
 }
 
-func ChangeFolder(aerc *widgets.Aerc, args []string) error {
+func (_ ChangeFolder) Execute(aerc *widgets.Aerc, args []string) error {
 	if len(args) != 2 {
 		return errors.New("Usage: cf <folder>")
 	}
diff --git a/commands/account/compose.go b/commands/account/compose.go
index aeb415e0..cafba787 100644
--- a/commands/account/compose.go
+++ b/commands/account/compose.go
@@ -6,12 +6,22 @@ import (
 	"git.sr.ht/~sircmpwn/aerc/widgets"
 )
 
+type Compose struct{}
+
 func init() {
-	register("compose", Compose)
+	register(Compose{})
+}
+
+func (_ Compose) Aliases() []string {
+	return []string{"compose"}
+}
+
+func (_ Compose) Complete(aerc *widgets.Aerc, args []string) []string {
+	return nil
 }
 
 // TODO: Accept arguments for default headers, message body
-func Compose(aerc *widgets.Aerc, args []string) error {
+func (_ Compose) Execute(aerc *widgets.Aerc, args []string) error {
 	if len(args) != 1 {
 		return errors.New("Usage: compose")
 	}
diff --git a/commands/account/mkdir.go b/commands/account/mkdir.go
index d2458217..be9b14a3 100644
--- a/commands/account/mkdir.go
+++ b/commands/account/mkdir.go
@@ -10,11 +10,21 @@ import (
 	"git.sr.ht/~sircmpwn/aerc/worker/types"
 )
 
+type MakeDir struct{}
+
 func init() {
-	register("mkdir", Mkdir)
+	register(MakeDir{})
+}
+
+func (_ MakeDir) Aliases() []string {
+	return []string{"mkdir"}
+}
+
+func (_ MakeDir) Complete(aerc *widgets.Aerc, args []string) []string {
+	return nil
 }
 
-func Mkdir(aerc *widgets.Aerc, args []string) error {
+func (_ MakeDir) Execute(aerc *widgets.Aerc, args []string) error {
 	if len(args) != 2 {
 		return errors.New("Usage: :mkdir <name>")
 	}
diff --git a/commands/account/next-folder.go b/commands/account/next-folder.go
index 6ad3d540..414e6063 100644
--- a/commands/account/next-folder.go
+++ b/commands/account/next-folder.go
@@ -8,16 +8,21 @@ import (
 	"git.sr.ht/~sircmpwn/aerc/widgets"
 )
 
+type NextPrevFolder struct{}
+
 func init() {
-	register("next-folder", NextPrevFolder)
-	register("prev-folder", NextPrevFolder)
+	register(NextPrevFolder{})
 }
 
-func nextPrevFolderUsage(cmd string) error {
-	return errors.New(fmt.Sprintf("Usage: %s [n]", cmd))
+func (_ NextPrevFolder) Aliases() []string {
+	return []string{"next-folder", "prev-folder"}
+}
+
+func (_ NextPrevFolder) Complete(aerc *widgets.Aerc, args []string) []string {
+	return nil
 }
 
-func NextPrevFolder(aerc *widgets.Aerc, args []string) error {
+func (_ NextPrevFolder) Execute(aerc *widgets.Aerc, args []string) error {
 	if len(args) > 2 {
 		return nextPrevFolderUsage(args[0])
 	}
@@ -44,3 +49,7 @@ func NextPrevFolder(aerc *widgets.Aerc, args []string) error {
 	}
 	return nil
 }
+
+func nextPrevFolderUsage(cmd string) error {
+	return errors.New(fmt.Sprintf("Usage: %s [n]", cmd))
+}
diff --git a/commands/account/next-result.go b/commands/account/next-result.go
index d89de564..24d53be7 100644
--- a/commands/account/next-result.go
+++ b/commands/account/next-result.go
@@ -7,16 +7,21 @@ import (
 	"git.sr.ht/~sircmpwn/aerc/widgets"
 )
 
+type NextPrevResult struct{}
+
 func init() {
-	register("next-result", NextPrevResult)
-	register("prev-result", NextPrevResult)
+	register(NextPrevResult{})
 }
 
-func nextPrevResultUsage(cmd string) error {
-	return errors.New(fmt.Sprintf("Usage: %s [<n>[%%]]", cmd))
+func (_ NextPrevResult) Aliases() []string {
+	return []string{"next-result", "prev-result"}
+}
+
+func (_ NextPrevResult) Complete(aerc *widgets.Aerc, args []string) []string {
+	return nil
 }
 
-func NextPrevResult(aerc *widgets.Aerc, args []string) error {
+func (_ NextPrevResult) Execute(aerc *widgets.Aerc, args []string) error {
 	if len(args) > 1 {
 		return nextPrevResultUsage(args[0])
 	}
@@ -39,3 +44,7 @@ func NextPrevResult(aerc *widgets.Aerc, args []string) error {
 	}
 	return nil
 }
+
+func nextPrevResultUsage(cmd string) error {
+	return errors.New(fmt.Sprintf("Usage: %s [<n>[%%]]", cmd))
+}
diff --git a/commands/account/next.go b/commands/account/next.go
index 3b9260c4..f306b480 100644
--- a/commands/account/next.go
+++ b/commands/account/next.go
@@ -9,18 +9,21 @@ import (
 	"git.sr.ht/~sircmpwn/aerc/widgets"
 )
 
+type NextPrevMsg struct{}
+
 func init() {
-	register("next", NextPrevMessage)
-	register("next-message", NextPrevMessage)
-	register("prev", NextPrevMessage)
-	register("prev-message", NextPrevMessage)
+	register(NextPrevMsg{})
 }
 
-func nextPrevMessageUsage(cmd string) error {
-	return errors.New(fmt.Sprintf("Usage: %s [<n>[%%]]", cmd))
+func (_ NextPrevMsg) Aliases() []string {
+	return []string{"next", "next-message", "prev", "prev-message"}
+}
+
+func (_ NextPrevMsg) Complete(aerc *widgets.Aerc, args []string) []string {
+	return nil
 }
 
-func NextPrevMessage(aerc *widgets.Aerc, args []string) error {
+func (_ NextPrevMsg) Execute(aerc *widgets.Aerc, args []string) error {
 	if len(args) > 2 {
 		return nextPrevMessageUsage(args[0])
 	}
@@ -63,3 +66,7 @@ func NextPrevMessage(aerc *widgets.Aerc, args []string) error {
 	}
 	return nil
 }
+
+func nextPrevMessageUsage(cmd string) error {
+	return errors.New(fmt.Sprintf("Usage: %s [<n>[%%]]", cmd))
+}
diff --git a/commands/account/pipe.go b/commands/account/pipe.go
index d3cc80ae..a68ef64e 100644
--- a/commands/account/pipe.go
+++ b/commands/account/pipe.go
@@ -8,11 +8,21 @@ import (
 	"git.sr.ht/~sircmpwn/aerc/widgets"
 )
 
+type Pipe struct{}
+
 func init() {
-	register("pipe", Pipe)
+	register(Pipe{})
+}
+
+func (_ Pipe) Aliases() []string {
+	return []string{"pipe"}
+}
+
+func (_ Pipe) Complete(aerc *widgets.Aerc, args []string) []string {
+	return nil
 }
 
-func Pipe(aerc *widgets.Aerc, args []string) error {
+func (_ Pipe) Execute(aerc *widgets.Aerc, args []string) error {
 	if len(args) < 2 {
 		return errors.New("Usage: :pipe <cmd> [args...]")
 	}
diff --git a/commands/account/search.go b/commands/account/search.go
index 513ad439..a8640dcc 100644
--- a/commands/account/search.go
+++ b/commands/account/search.go
@@ -9,12 +9,21 @@ import (
 	"git.sr.ht/~sircmpwn/aerc/widgets"
 )
 
+type SearchFilter struct{}
+
 func init() {
-	register("search", SearchFilter)
-	//register("filter", SearchFilter) // TODO
+	register(SearchFilter{})
+}
+
+func (_ SearchFilter) Aliases() []string {
+	return []string{"search"}
+}
+
+func (_ SearchFilter) Complete(aerc *widgets.Aerc, args []string) []string {
+	return nil
 }
 
-func SearchFilter(aerc *widgets.Aerc, args []string) error {
+func (_ SearchFilter) Execute(aerc *widgets.Aerc, args []string) error {
 	var (
 		criteria *imap.SearchCriteria = imap.NewSearchCriteria()
 	)
diff --git a/commands/account/select.go b/commands/account/select.go
index 707f6c98..70e08ac6 100644
--- a/commands/account/select.go
+++ b/commands/account/select.go
@@ -7,12 +7,21 @@ import (
 	"git.sr.ht/~sircmpwn/aerc/widgets"
 )
 
+type SelectMessage struct{}
+
 func init() {
-	register("select", SelectMessage)
-	register("select-message", SelectMessage)
+	register(SelectMessage{})
+}
+
+func (_ SelectMessage) Aliases() []string {
+	return []string{"select", "select-message"}
+}
+
+func (_ SelectMessage) Complete(aerc *widgets.Aerc, args []string) []string {
+	return nil
 }
 
-func SelectMessage(aerc *widgets.Aerc, args []string) error {
+func (_ SelectMessage) Execute(aerc *widgets.Aerc, args []string) error {
 	if len(args) != 2 {
 		return errors.New("Usage: :select-message <n>")
 	}
diff --git a/commands/account/view.go b/commands/account/view.go
index f7f3ec64..cec65aa9 100644
--- a/commands/account/view.go
+++ b/commands/account/view.go
@@ -6,12 +6,21 @@ import (
 	"git.sr.ht/~sircmpwn/aerc/widgets"
 )
 
+type ViewMessage struct{}
+
 func init() {
-	register("view", ViewMessage)
-	register("view-message", ViewMessage)
+	register(ViewMessage{})
+}
+
+func (_ ViewMessage) Aliases() []string {
+	return []string{"view-message", "view"}
+}
+
+func (_ ViewMessage) Complete(aerc *widgets.Aerc, args []string) []string {
+	return nil
 }
 
-func ViewMessage(aerc *widgets.Aerc, args []string) error {
+func (_ ViewMessage) Execute(aerc *widgets.Aerc, args []string) error {
 	if len(args) != 1 {
 		return errors.New("Usage: view-message")
 	}