Make tty_indexed.go respond to None like tty_truecolour.go (#869)

formatters/tty_indexed.go

@@ -242,12 +242,21 @@ func (c *indexedTTYFormatter) Format(w io.Writer, style *chroma.Style, it chroma
 	theme := styleToEscapeSequence(c.table, style)
 	for token := it(); token != chroma.EOF; token = it() {
 		clr, ok := theme[token.Type]
+
+		// This search mimics how styles.Get() is used in tty_truecolour.go.
 		if !ok {
 			clr, ok = theme[token.Type.SubCategory()]
 			if !ok {
-				clr = theme[token.Type.Category()]
+				clr, ok = theme[token.Type.Category()]
+				if !ok {
+					clr, ok = theme[chroma.Text]
+					if !ok {
+						clr = theme[chroma.Background]
+					}
+				}
 			}
 		}
+
 		if clr != "" {
 			fmt.Fprint(w, clr)
 		}

formatters/tty_indexed_test.go

@@ -1,6 +1,7 @@
 package formatters
 
 import (
+	"strings"
 	"testing"
 
 	assert "github.com/alecthomas/assert/v2"
@@ -11,3 +12,25 @@ func TestClosestColour(t *testing.T) {
 	actual := findClosest(ttyTables[256], chroma.MustParseColour("#e06c75"))
 	assert.Equal(t, chroma.MustParseColour("#d75f87"), actual)
 }
+
+func TestNoneColour(t *testing.T) {
+	formatter := TTY256
+	tokenType := chroma.None
+
+	style, err := chroma.NewStyle("test", chroma.StyleEntries{
+		chroma.Background: "#D0ab1e",
+	})
+	assert.NoError(t, err)
+
+	stringBuilder := strings.Builder{}
+	err = formatter.Format(&stringBuilder, style, chroma.Literator(chroma.Token{
+		Type:  tokenType,
+		Value: "WORD",
+	}))
+	assert.NoError(t, err)
+
+	// "178" = #d7af00 approximates #d0ab1e
+	//
+	// 178 color ref: https://jonasjacek.github.io/colors/
+	assert.Equal(t, "\033[38;5;178mWORD\033[0m", stringBuilder.String())
+}