Be clearer when LESS_TERMCAP_xx are invalid

Relates to #170.

m/styling.go

@@ -26,7 +26,12 @@ func setStyle(updateMe *twin.Style, envVarName string, fallback *twin.Style) {
 		return
 	}
 
-	*updateMe = termcapToStyle(envValue)
+	style, err := TermcapToStyle(envValue)
+	if err != nil {
+		*updateMe = style
+	}
+
+	log.Debug("Ignoring invalid ", envVarName, ": ", strings.ReplaceAll(envValue, "\x1b", "ESC"), ": ", err)
 }
 
 // With exact set, only return a style if the Chroma formatter has an explicit
@@ -85,20 +90,19 @@ func consumeLessTermcapEnvs(chromaStyle *chroma.Style, chromaFormatter *chroma.F
 		twinStyleFromChroma(chromaStyle, chromaFormatter, chroma.GenericUnderline, false),
 	)
 
-	headingStyle := twinStyleFromChroma(chromaStyle, chromaFormatter, chroma.GenericHeading, true)
-	if headingStyle != nil {
-		textstyles.ManPageHeading = *headingStyle
-	}
-
 	// Since standoutStyle defaults to nil we can't just pass it to setStyle().
 	// Instead we give it special treatment here and set it only if its
 	// environment variable is set.
 	//
 	// Ref: https://github.com/walles/moar/issues/171
 	envValue := os.Getenv("LESS_TERMCAP_so")
 	if envValue != "" {
-		style := termcapToStyle(envValue)
-		standoutStyle = &style
+		style, err := TermcapToStyle(envValue)
+		if err == nil {
+			standoutStyle = &style
+		} else {
+			log.Debug("Ignoring invalid LESS_TERMCAP_so: ", strings.ReplaceAll(envValue, "\x1b", "ESC"), ": ", err)
+		}
 	}
 }
 
@@ -107,6 +111,11 @@ func styleUI(chromaStyle *chroma.Style, chromaFormatter *chroma.Formatter, statu
 		return
 	}
 
+	headingStyle := twinStyleFromChroma(chromaStyle, chromaFormatter, chroma.GenericHeading, true)
+	if headingStyle != nil {
+		textstyles.ManPageHeading = *headingStyle
+	}
+
 	chromaLineNumbers := twinStyleFromChroma(chromaStyle, chromaFormatter, chroma.LineNumbers, true)
 	if chromaLineNumbers != nil {
 		// If somebody can provide an example where not-dimmed line numbers
@@ -139,8 +148,11 @@ func styleUI(chromaStyle *chroma.Style, chromaFormatter *chroma.Formatter, statu
 	}
 }
 
-func termcapToStyle(termcap string) twin.Style {
+func TermcapToStyle(termcap string) (twin.Style, error) {
 	// Add a character to be sure we have one to take the format from
 	cells := textstyles.CellsFromString("", termcap+"x", nil).Cells
-	return cells[len(cells)-1].Style
+	if len(cells) != 1 {
+		return twin.StyleDefault, fmt.Errorf("Expected styling only and no text")
+	}
+	return cells[len(cells)-1].Style, nil
 }

moar.go

@@ -33,10 +33,27 @@ func printUsageEnvVar(output io.Writer, envVarName string, description string) {
 		return
 	}
 
+	style, err := m.TermcapToStyle(value)
+	if err != nil {
+		bold := twin.StyleDefault.WithAttr(twin.AttrBold).RenderUpdateFrom(twin.StyleDefault, twin.ColorType256)
+		notBold := twin.StyleDefault.RenderUpdateFrom(twin.StyleDefault.WithAttr(twin.AttrBold), twin.ColorType256)
+		_, _ = fmt.Fprintf(output, "  %s (%s): %s %s<- Error: %v%s\n",
+			envVarName,
+			description,
+			strings.ReplaceAll(value, "\x1b", "ESC"),
+			bold,
+			err,
+			notBold,
+		)
+		return
+	}
+
+	prefix := style.RenderUpdateFrom(twin.StyleDefault, twin.ColorType256)
+	suffix := twin.StyleDefault.RenderUpdateFrom(style, twin.ColorType256)
 	_, _ = fmt.Fprintf(output, "  %s (%s): %s\n",
 		envVarName,
 		description,
-		strings.ReplaceAll(value, "\x1b", "ESC"),
+		prefix+strings.ReplaceAll(value, "\x1b", "ESC")+suffix,
 	)
 }