Allow empty Y-axis labels on linechart using a value formatter that returns empty strings

Signed-off-by: Xabier Larrakoetxea <slok69@gmail.com>

internal/alignfor/align.go

@@ -90,14 +90,17 @@ func Rectangle(rect image.Rectangle, ar image.Rectangle, h align.Horizontal, v a
 // Text aligns the text within the given rectangle, returns the start point for the text.
 // For the purposes of the alignment this assumes that text will be trimmed if
 // it overruns the rectangle.
-// This only supports a single line of text, the text must not contain non-printable characters.
+// This only supports a single line of text, the text must not contain non-printable characters,
+// allows empty text.
 func Text(rect image.Rectangle, text string, h align.Horizontal, v align.Vertical) (image.Point, error) {
 	if strings.ContainsRune(text, '\n') {
 		return image.ZP, fmt.Errorf("the provided text contains a newline character: %q", text)
 	}
 
-	if err := wrap.ValidText(text); err != nil {
-		return image.ZP, fmt.Errorf("the provided text contains non printable character(s): %s", err)
+	if text != "" {
+		if err := wrap.ValidText(text); err != nil {
+			return image.ZP, fmt.Errorf("the provided text contains non printable character(s): %s", err)
+		}
 	}
 
 	cells := runewidth.StringWidth(text)

internal/wrap/wrap.go

@@ -59,8 +59,8 @@ const (
 )
 
 // ValidText validates the provided text for wrapping.
-// The text must not contain any control or space characters other
-// than '\n' and ' '.
+// The text must not be empty, contain any control or
+// space characters other than '\n' and ' '.
 func ValidText(text string) error {
 	if text == "" {
 		return errors.New("the text cannot be empty")

widgets/linechart/internal/axes/label.go

@@ -71,7 +71,7 @@ func yLabels(scale *YScale, labelWidth int) ([]*Label, error) {
 	if min := 2; scale.GraphHeight < min {
 		return nil, fmt.Errorf("cannot place labels on a canvas with height %d, minimum is %d", scale.GraphHeight, min)
 	}
-	if min := 1; labelWidth < min {
+	if min := 0; labelWidth < min {
 		return nil, fmt.Errorf("cannot place labels in label area width %d, minimum is %d", labelWidth, min)
 	}
 

widgets/linechart/internal/axes/label_test.go

@@ -45,7 +45,7 @@ func TestYLabels(t *testing.T) {
 			min:         0,
 			max:         1,
 			graphHeight: 2,
-			labelWidth:  0,
+			labelWidth:  -1,
 			wantErr:     true,
 		},
 		{

widgets/linechart/linechart_test.go

@@ -1692,7 +1692,31 @@ func TestLineChartDraws(t *testing.T) {
 			writes: func(lc *LineChart) error {
 				return lc.Series("first", []float64{0, 100})
 			},
-			wantDrawErr: true,
+			wantCapacity: 38,
+			want: func(size image.Point) *faketerm.Terminal {
+				ft := faketerm.MustNew(size)
+				c := testcanvas.MustNew(ft.Area())
+
+				// Y and X axis.
+				lines := []draw.HVLine{
+					{Start: image.Point{0, 0}, End: image.Point{0, 8}},
+					{Start: image.Point{0, 8}, End: image.Point{19, 8}},
+				}
+				testdraw.MustHVLines(c, lines)
+
+				// Value labels.
+				testdraw.MustText(c, "0", image.Point{1, 9})
+				testdraw.MustText(c, "1", image.Point{19, 9})
+
+				// Braille line.
+				graphAr := image.Rect(1, 0, 20, 8)
+				bc := testbraille.MustNew(graphAr)
+				testdraw.MustBrailleLine(bc, image.Point{0, 31}, image.Point{36, 0})
+				testbraille.MustCopyTo(bc, c)
+
+				testcanvas.MustApply(c, ft)
+				return ft
+			},
 		},
 		{
 			desc:   "custom Y-axis labels using a value formatter that returns very long strings",