Apply relevant msglist styles in order

Allow styles to be layered over a base style. The list of styles to
apply is layered over the base style in order, such that if the layer
does not differ from the base it is not used. The order that these
styles are applied in is, from first to last:

msglist_default
msglist_unread
msglist_read    (exclusive with unread, so technically the same level)
msglist_flagged
msglist_deleted
msglist_marked

So, msglist_marked style dominates.

This fixes an issue where the msglist_deleted style was not being applied.

config/config.go

@@ -699,3 +699,12 @@ func (uiConfig UIConfig) GetStyle(so StyleObject) tcell.Style {
 func (uiConfig UIConfig) GetStyleSelected(so StyleObject) tcell.Style {
 	return uiConfig.style.Selected(so)
 }
+
+func (uiConfig UIConfig) GetComposedStyle(base StyleObject,
+	styles []StyleObject) tcell.Style {
+	return uiConfig.style.Compose(base, styles)
+}
+
+func (uiConfig UIConfig) GetComposedStyleSelected(base StyleObject, styles []StyleObject) tcell.Style {
+	return uiConfig.style.ComposeSelected(base, styles)
+}

config/style.go

@@ -31,9 +31,9 @@ const (
 	STYLE_MSGLIST_DEFAULT
 	STYLE_MSGLIST_UNREAD
 	STYLE_MSGLIST_READ
+	STYLE_MSGLIST_FLAGGED
 	STYLE_MSGLIST_DELETED
 	STYLE_MSGLIST_MARKED
-	STYLE_MSGLIST_FLAGGED
 
 	STYLE_DIRLIST_DEFAULT
 
@@ -67,9 +67,9 @@ var StyleNames = map[string]StyleObject{
 	"msglist_default": STYLE_MSGLIST_DEFAULT,
 	"msglist_unread":  STYLE_MSGLIST_UNREAD,
 	"msglist_read":    STYLE_MSGLIST_READ,
+	"msglist_flagged": STYLE_MSGLIST_FLAGGED,
 	"msglist_deleted": STYLE_MSGLIST_DELETED,
 	"msglist_marked":  STYLE_MSGLIST_MARKED,
-	"msglist_flagged": STYLE_MSGLIST_FLAGGED,
 
 	"dirlist_default": STYLE_DIRLIST_DEFAULT,
 
@@ -180,6 +180,31 @@ func (s *Style) Set(attr, val string) error {
 	return nil
 }
 
+func (s Style) composeWith(styles []*Style) Style {
+	newStyle := s
+	for _, st := range styles {
+		if st.Fg != s.Fg {
+			newStyle.Fg = st.Fg
+		}
+		if st.Bg != s.Bg {
+			newStyle.Bg = st.Bg
+		}
+		if st.Bold != s.Bold {
+			newStyle.Bold = st.Bold
+		}
+		if st.Blink != s.Blink {
+			newStyle.Blink = st.Blink
+		}
+		if st.Underline != s.Underline {
+			newStyle.Underline = st.Underline
+		}
+		if st.Reverse != s.Reverse {
+			newStyle.Reverse = st.Reverse
+		}
+	}
+	return newStyle
+}
+
 type StyleSet struct {
 	objects  map[StyleObject]*Style
 	selected map[StyleObject]*Style
@@ -213,6 +238,27 @@ func (ss StyleSet) Selected(so StyleObject) tcell.Style {
 	return ss.selected[so].Get()
 }
 
+func (ss StyleSet) Compose(so StyleObject, sos []StyleObject) tcell.Style {
+	base := *ss.objects[so]
+	styles := make([]*Style, len(sos))
+	for i, so := range sos {
+		styles[i] = ss.objects[so]
+	}
+
+	return base.composeWith(styles).Get()
+}
+
+func (ss StyleSet) ComposeSelected(so StyleObject,
+	sos []StyleObject) tcell.Style {
+	base := *ss.selected[so]
+	styles := make([]*Style, len(sos))
+	for i, so := range sos {
+		styles[i] = ss.selected[so]
+	}
+
+	return base.composeWith(styles).Get()
+}
+
 func findStyleSet(stylesetName string, stylesetsDir []string) (string, error) {
 	for _, dir := range stylesetsDir {
 		stylesetPath, err := homedir.Expand(path.Join(dir, stylesetName))

doc/aerc-stylesets.7.scd

@@ -107,12 +107,12 @@ styling.
 :  Unread messages in a message list.
 |  msglist_read
 :  Read messages in a message list.
+|  msglist_flagged
+:  The messages with the flagged flag.
 |  msglist_deleted
 :  The messages marked as deleted.
 |  msglist_marked
 :  The messages with the marked flag.
-|  msglist_flagged
-:  The messages with the flagged flag.
 |  dirlist_default
 :  The default style for directories in the directory list.
 |  completion_default
@@ -175,6 +175,23 @@ If we specify the global style selected modifer using fnmatch as below:
 
 This toggles the reverse switch for selected version of all the style objects.
 
+## Layered styles
+Some styles, (currently only the `msglist\*` ones) are applied in layers. If
+a style differs from the base (in this case `msglist_default`) then that style
+applies, unless overridden by a higher layer. The order that `msglist` styles
+are applied in is, from first to last:
+
+```
+msglist_default
+msglist_unread
+msglist_read
+msglist_flagged
+msglist_deleted
+msglist_marked
+```
+
+So, the marked style will override all other msglist styles.
+
 ## Colors
 The color values are set using the values accepted by the tcell library.
 The values can be one of the following.

widgets/msglist.go

@@ -108,12 +108,7 @@ func (ml *MessageList) Draw(ctx *ui.Context) {
 			config.UI_CONTEXT_SUBJECT: msg.Envelope.Subject,
 		})
 
-		so := config.STYLE_MSGLIST_DEFAULT
+		msg_styles := []config.StyleObject{}
-
-		// deleted message
-		if _, ok := store.Deleted[msg.Uid]; ok {
-			so = config.STYLE_MSGLIST_DELETED
-		}
 		// unread message
 		seen := false
 		flagged := false
@@ -127,25 +122,31 @@ func (ml *MessageList) Draw(ctx *ui.Context) {
 		}
 
 		if seen {
-			so = config.STYLE_MSGLIST_READ
+			msg_styles = append(msg_styles, config.STYLE_MSGLIST_READ)
 		} else {
-			so = config.STYLE_MSGLIST_UNREAD
+			msg_styles = append(msg_styles, config.STYLE_MSGLIST_UNREAD)
 		}
 
 		if flagged {
-			so = config.STYLE_MSGLIST_FLAGGED
+			msg_styles = append(msg_styles, config.STYLE_MSGLIST_FLAGGED)
+		}
+
+		// deleted message
+		if _, ok := store.Deleted[msg.Uid]; ok {
+			msg_styles = append(msg_styles, config.STYLE_MSGLIST_DELETED)
 		}
 
 		// marked message
 		if store.IsMarked(msg.Uid) {
-			so = config.STYLE_MSGLIST_MARKED
+			msg_styles = append(msg_styles, config.STYLE_MSGLIST_MARKED)
 		}
 
-		style := uiConfig.GetStyle(so)
+		var style tcell.Style
-
 		// current row
 		if row == ml.store.SelectedIndex()-ml.scroll {
-			style = uiConfig.GetStyleSelected(so)
+			style = uiConfig.GetComposedStyleSelected(config.STYLE_MSGLIST_DEFAULT, msg_styles)
+		} else {
+			style = uiConfig.GetComposedStyle(config.STYLE_MSGLIST_DEFAULT, msg_styles)
 		}
 
 		ctx.Fill(0, row, ctx.Width(), 1, ' ', style)