Fix display width of common punctuation characters

mislav · mislav · commit 1f86e7cd0495 · 2020-09-02T20:59:11.000+02:00
These characters get classified as "East Asian Mixed" by Go's
`text/width` package, and thus assumed that their printed version
occupies a width of 2 characters, whereas they each only occupy one.

I'm not sure why they are classified as East Asian, but I did not have
the energy to dive into Go's Unicode tables, so here is a workaround
based on an exclusion list.
diff --git a/pkg/text/truncate.go b/pkg/text/truncate.go
@@ -53,7 +53,24 @@ func Truncate(max int, s string) string {
 	return res
 }
 
+var runeDisplayWidthOverrides = map[rune]int{
+	'“': 1,
+	'”': 1,
+	'‘': 1,
+	'’': 1,
+	'–': 1, // en dash
+	'—': 1, // em dash
+	'→': 1,
+	'…': 1,
+	'•': 1, // bullet
+	'·': 1, // middle dot
+}
+
 func runeDisplayWidth(r rune) int {
+	if w, ok := runeDisplayWidthOverrides[r]; ok {
+		return w
+	}
+
 	switch width.LookupRune(r).Kind() {
 	case width.EastAsianWide, width.EastAsianAmbiguous, width.EastAsianFullwidth:
 		return 2
diff --git a/pkg/text/truncate_test.go b/pkg/text/truncate_test.go
@@ -1,6 +1,8 @@
 package text
 
-import "testing"
+import (
+	"testing"
+)
 
 func TestTruncate(t *testing.T) {
 	type args struct {
@@ -69,3 +71,69 @@ func TestTruncate(t *testing.T) {
 		})
 	}
 }
+
+func TestDisplayWidth(t *testing.T) {
+	tests := []struct {
+		name string
+		text string
+		want int
+	}{
+		{
+			name: "check mark",
+			text: `✓`,
+			want: 1,
+		},
+		{
+			name: "bullet icon",
+			text: `•`,
+			want: 1,
+		},
+		{
+			name: "middle dot",
+			text: `·`,
+			want: 1,
+		},
+		{
+			name: "ellipsis",
+			text: `…`,
+			want: 1,
+		},
+		{
+			name: "right arrow",
+			text: `→`,
+			want: 1,
+		},
+		{
+			name: "smart double quotes",
+			text: `“”`,
+			want: 2,
+		},
+		{
+			name: "smart single quotes",
+			text: `‘’`,
+			want: 2,
+		},
+		{
+			name: "em dash",
+			text: `—`,
+			want: 1,
+		},
+		{
+			name: "en dash",
+			text: `–`,
+			want: 1,
+		},
+		{
+			name: "emoji",
+			text: `👍`,
+			want: 2,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := DisplayWidth(tt.text); got != tt.want {
+				t.Errorf("DisplayWidth() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
