textinput: render the full placeholder when Width is 0

textinput/textinput.go

@@ -745,8 +745,19 @@ func (m Model) placeholderView() string {
 		render = styles.Placeholder.Render
 	)
 
-	p := make([]rune, m.Width()+1)
-	copy(p, []rune(m.Placeholder))
+	// Size the buffer to the longer of Width and the placeholder
+	// itself so that, when Width is 0 ("no width") or shorter than
+	// the placeholder, copy still pulls in every rune. The old
+	// `m.Width()+1` left exactly one slot when Width was 0, so all
+	// but the first character of the placeholder fell on the floor.
+	// See #950.
+	placeholderRunes := []rune(m.Placeholder)
+	size := m.Width() + 1
+	if size < len(placeholderRunes) {
+		size = len(placeholderRunes)
+	}
+	p := make([]rune, size)
+	copy(p, placeholderRunes)
 
 	m.virtualCursor.TextStyle = styles.Placeholder
 	m.virtualCursor.SetChar(string(p[:1]))

textinput/textinput_test.go

@@ -48,6 +48,28 @@ func Test_SlicingOutsideCap(t *testing.T) {
 	textinput.View()
 }
 
+// Regression for #950. When SetWidth(0) is used (the documented
+// "no width" mode), the placeholder buffer was sized to exactly 1
+// rune and copy lost everything past the first character. The
+// rendered placeholder was a single letter regardless of length.
+func TestPlaceholderZeroWidth(t *testing.T) {
+	ti := New()
+	ti.Placeholder = "Something"
+	ti.SetWidth(0)
+
+	got := ti.View()
+	// View output carries ANSI styling, so check each rune of the
+	// placeholder appears somewhere in the string in order.
+	idx := 0
+	for _, r := range "Something" {
+		i := strings.IndexRune(got[idx:], r)
+		if i < 0 {
+			t.Fatalf("expected full placeholder %q to appear in view %q", "Something", got)
+		}
+		idx += i + 1
+	}
+}
+
 func TestChinesePlaceholder(t *testing.T) {
 	t.Skip("Skipping flaky test, the returned view seems incorrect. TODO: Needs investigation.")
 	textinput := New()