Add option to always show mimetype in viewer

A user may want to be able to see what mimetype they are viewing, so
that they can determine what program it may be opened in or for some
other reason.

The config option is under the [viewer] section and is called
'always-show-mime'. It defaults to false to preserve the current
behaviour.

config/aerc.conf.in

@@ -69,6 +69,11 @@ show-headers=false
 # Default: From|To,Cc|Bcc,Date,Subject
 header-layout=From|To,Cc|Bcc,Date,Subject
 
+# Whether to always show the mimetype of an email, even when it is just a single part
+#
+# Default: false
+always-show-mime=false
+
 [compose]
 #
 # Specifies the command to run the editor with. It will be shown in an embedded

config/config.go

@@ -80,6 +80,7 @@ type ViewerConfig struct {
 	Pager          string
 	Alternatives   []string
 	ShowHeaders    bool `ini:"show-headers"`
+	AlwaysShowMime bool `ini:"always-show-mime"`
 	HeaderLayout   [][]string `ini:"-"`
 }
 

doc/aerc-config.5.scd

@@ -133,6 +133,11 @@ These options are configured in the *[viewer]* section of aerc.conf.
 
 	Default: false
 
+*always-show-mime*
+	Whether to always show the mimetype of an email, even when it is just a single part.
+
+	Default: false
+
 ## COMPOSE
 
 These options are configured in the *[compose]* section of aerc.conf.

widgets/msgviewer.go

@@ -41,6 +41,7 @@ type PartSwitcher struct {
 	parts          []*PartViewer
 	selected       int
 	showHeaders    bool
+	alwaysShowMime bool
 }
 
 func NewMessageViewer(acct *AccountView, conf *config.AercConfig,
@@ -165,6 +166,7 @@ func createSwitcher(switcher *PartSwitcher, conf *config.AercConfig,
 	store *lib.MessageStore, msg *models.MessageInfo) error {
 	var err error
 	switcher.showHeaders = conf.Viewer.ShowHeaders
+	switcher.alwaysShowMime = conf.Viewer.AlwaysShowMime
 
 	if len(msg.BodyStructure.Parts) == 0 {
 		switcher.selected = 0
@@ -312,7 +314,7 @@ func (ps *PartSwitcher) Event(event tcell.Event) bool {
 
 func (ps *PartSwitcher) Draw(ctx *ui.Context) {
 	height := len(ps.parts)
-	if height == 1 {
+	if height == 1 && !ps.alwaysShowMime {
 		ps.parts[ps.selected].Draw(ctx)
 		return
 	}