Pager friendly terminal formatting

formatters/tty_indexed.go

@@ -1,7 +1,6 @@
 package formatters
 
 import (
-	"fmt"
 	"io"
 	"math"
 
@@ -257,13 +256,7 @@ func (c *indexedTTYFormatter) Format(w io.Writer, style *chroma.Style, it chroma
 			}
 		}
 
-		if clr != "" {
-			fmt.Fprint(w, clr)
-		}
-		fmt.Fprint(w, token.Value)
-		if clr != "" {
-			fmt.Fprintf(w, "\033[0m")
-		}
+		writeToken(w, clr, token.Value)
 	}
 	return nil
 }

formatters/tty_truecolour.go

@@ -3,40 +3,74 @@ package formatters
 import (
 	"fmt"
 	"io"
+	"regexp"
 
 	"github.com/alecthomas/chroma/v2"
 )
 
 // TTY16m is a true-colour terminal formatter.
 var TTY16m = Register("terminal16m", chroma.FormatterFunc(trueColourFormatter))
 
+var crOrCrLf = regexp.MustCompile(`\r?\n`)
+
+// Print the text with the given formatting, resetting the formatting at the end
+// of each line and resuming it on the next line.
+//
+// This way, a pager (like https://github.com/walles/moar for example) can show
+// any line in the output by itself, and it will get the right formatting.
+func writeToken(w io.Writer, formatting string, text string) {
+	if formatting == "" {
+		fmt.Fprint(w, text)
+		return
+	}
+
+	newlineIndices := crOrCrLf.FindAllStringIndex(text, -1)
+
+	afterLastNewline := 0
+	for _, indices := range newlineIndices {
+		newlineStart, afterNewline := indices[0], indices[1]
+		fmt.Fprint(w, formatting)
+		fmt.Fprint(w, text[afterLastNewline:newlineStart])
+		fmt.Fprint(w, "\033[0m")
+		fmt.Fprint(w, text[newlineStart:afterNewline])
+		afterLastNewline = afterNewline
+	}
+
+	if afterLastNewline < len(text) {
+		// Print whatever is left after the last newline
+		fmt.Fprint(w, formatting)
+		fmt.Fprint(w, text[afterLastNewline:])
+		fmt.Fprint(w, "\033[0m")
+	}
+}
+
 func trueColourFormatter(w io.Writer, style *chroma.Style, it chroma.Iterator) error {
 	style = clearBackground(style)
 	for token := it(); token != chroma.EOF; token = it() {
 		entry := style.Get(token.Type)
-		if !entry.IsZero() {
-			out := ""
-			if entry.Bold == chroma.Yes {
-				out += "\033[1m"
-			}
-			if entry.Underline == chroma.Yes {
-				out += "\033[4m"
-			}
-			if entry.Italic == chroma.Yes {
-				out += "\033[3m"
-			}
-			if entry.Colour.IsSet() {
-				out += fmt.Sprintf("\033[38;2;%d;%d;%dm", entry.Colour.Red(), entry.Colour.Green(), entry.Colour.Blue())
-			}
-			if entry.Background.IsSet() {
-				out += fmt.Sprintf("\033[48;2;%d;%d;%dm", entry.Background.Red(), entry.Background.Green(), entry.Background.Blue())
-			}
-			fmt.Fprint(w, out)
+		if entry.IsZero() {
+			fmt.Fprint(w, token.Value)
+			continue
+		}
+
+		formatting := ""
+		if entry.Bold == chroma.Yes {
+			formatting += "\033[1m"
+		}
+		if entry.Underline == chroma.Yes {
+			formatting += "\033[4m"
 		}
-		fmt.Fprint(w, token.Value)
-		if !entry.IsZero() {
-			fmt.Fprint(w, "\033[0m")
+		if entry.Italic == chroma.Yes {
+			formatting += "\033[3m"
 		}
+		if entry.Colour.IsSet() {
+			formatting += fmt.Sprintf("\033[38;2;%d;%d;%dm", entry.Colour.Red(), entry.Colour.Green(), entry.Colour.Blue())
+		}
+		if entry.Background.IsSet() {
+			formatting += fmt.Sprintf("\033[48;2;%d;%d;%dm", entry.Background.Red(), entry.Background.Green(), entry.Background.Blue())
+		}
+
+		writeToken(w, formatting, token.Value)
 	}
 	return nil
 }