Calculate string width based on runes, not bytes

columnize.go

@@ -97,6 +97,15 @@ func elementsFromLine(config *Config, line string) []interface{} {
 	return elements
 }
 
+// runeLen calculates the number of visible "characters" in a string
+func runeLen(s string) int {
+	l := 0
+	for _ = range s {
+		l++
+	}
+	return l
+}
+
 // widthsFromLines examines a list of strings and determines how wide each
 // column should be considering all of the elements that need to be printed
 // within it.
@@ -106,7 +115,7 @@ func widthsFromLines(config *Config, lines []string) []int {
 	for _, line := range lines {
 		elems := elementsFromLine(config, line)
 		for i := 0; i < len(elems); i++ {
-			l := len(elems[i].(string))
+			l := runeLen(elems[i].(string))
 			if len(widths) <= i {
 				widths = append(widths, l)
 			} else if widths[i] < l {

columnize_test.go

@@ -75,7 +75,30 @@ func TestColumnWidthCalculator(t *testing.T) {
 	expected += "short          short          short"
 
 	if output != expected {
-		t.Fatalf("\nexpected:\n%s\n\ngot:\n%s", expected, output)
+		printableProof := fmt.Sprintf("\nGot:      %+q", output)
+		printableProof += fmt.Sprintf("\nExpected: %+q", expected)
+		t.Fatalf("\n%s", printableProof)
+	}
+}
+
+func TestColumnWidthCalculatorNonASCII(t *testing.T) {
+	input := []string{
+		"Column A | Column B | Column C",
+		"⌘⌘⌘⌘⌘⌘⌘⌘ | Longer than B | Longer than C",
+		"short | short | short",
+	}
+
+	config := DefaultConfig()
+	output := Format(input, config)
+
+	expected := "Column A  Column B       Column C\n"
+	expected += "⌘⌘⌘⌘⌘⌘⌘⌘  Longer than B  Longer than C\n"
+	expected += "short     short          short"
+
+	if output != expected {
+		printableProof := fmt.Sprintf("\nGot:      %+q", output)
+		printableProof += fmt.Sprintf("\nExpected: %+q", expected)
+		t.Fatalf("\n%s", printableProof)
 	}
 }