Fix re-rendering when prompt is exactly the width of the terminal (#321)

* Fix re-rendering when prompt is exactly the width of the terminal

The code that measures width of rendered lines of content and whether
any have overflown in the terminal did not account for the possibility
that the content could be _exactly_ the width of the terminal. In that
case, it shouldn't be counted as overflow.

* Reduce test dependencies by going straight to `pty`

This skips the go-expect & vt10x dependencies when stubbing only
terminal size and goes straight to the `creack/pty` library, which is
already used by go-expect under its old name, `kr/pty`.

* Use old name of `creack/pty` since it was already vendored

go.mod

@@ -5,7 +5,7 @@ require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/hinshun/vt10x v0.0.0-20180616224451-1954e6464174
 	github.com/kballard/go-shellquote v0.0.0-20180428030007-95032a82bc51
-	github.com/kr/pty v1.1.4 // indirect
+	github.com/kr/pty v1.1.4
 	github.com/mattn/go-colorable v0.1.2 // indirect
 	github.com/mattn/go-isatty v0.0.8
 	github.com/mgutz/ansi v0.0.0-20170206155736-9520e82c474b

renderer.go

@@ -148,8 +148,15 @@ func (r *Renderer) countLines(buf bytes.Buffer) int {
 			delim = len(bufBytes) // no new line found, read rest of text
 		}
 
-		// account for word wrapping
-		count += int(utf8.RuneCount(bufBytes[curr:delim]) / w)
+		if lineWidth := utf8.RuneCount(bufBytes[curr:delim]); lineWidth > w {
+			// account for word wrapping
+			count += lineWidth / w
+			if (lineWidth % w) == 0 {
+				// content whose width is exactly a multiplier of available width should not
+				// count as having wrapped on the last line
+				count -= 1
+			}
+		}
 		curr = delim + 1
 	}
 

renderer_posix_test.go

@@ -0,0 +1,91 @@
+// +build !windows
+
+package survey
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	"github.com/AlecAivazis/survey/v2/terminal"
+	pseudotty "github.com/kr/pty"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestRenderer_countLines(t *testing.T) {
+	t.Parallel()
+
+	termWidth := 72
+	pty, tty, err := pseudotty.Open()
+	require.Nil(t, err)
+	defer pty.Close()
+	defer tty.Close()
+
+	err = pseudotty.Setsize(tty, &pseudotty.Winsize{
+		Rows: 30,
+		Cols: uint16(termWidth),
+	})
+	require.Nil(t, err)
+
+	r := Renderer{
+		stdio: terminal.Stdio{
+			In:  tty,
+			Out: tty,
+			Err: tty,
+		},
+	}
+
+	tests := []struct {
+		name  string
+		buf   *bytes.Buffer
+		wants int
+	}{
+		{
+			name:  "empty",
+			buf:   new(bytes.Buffer),
+			wants: 0,
+		},
+		{
+			name:  "no newline",
+			buf:   bytes.NewBufferString("hello"),
+			wants: 0,
+		},
+		{
+			name:  "short line",
+			buf:   bytes.NewBufferString("hello\n"),
+			wants: 1,
+		},
+		{
+			name:  "three short lines",
+			buf:   bytes.NewBufferString("hello\nbeautiful\nworld\n"),
+			wants: 3,
+		},
+		{
+			name:  "full line",
+			buf:   bytes.NewBufferString(strings.Repeat("A", termWidth) + "\n"),
+			wants: 1,
+		},
+		{
+			name:  "overflow",
+			buf:   bytes.NewBufferString(strings.Repeat("A", termWidth+1) + "\n"),
+			wants: 2,
+		},
+		{
+			name:  "overflow fills 2nd line",
+			buf:   bytes.NewBufferString(strings.Repeat("A", termWidth*2) + "\n"),
+			wants: 2,
+		},
+		{
+			name:  "overflow spills to 3rd line",
+			buf:   bytes.NewBufferString(strings.Repeat("A", termWidth*2+1) + "\n"),
+			wants: 3,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			n := r.countLines(*tt.buf)
+			assert.Equal(t, tt.wants, n)
+		})
+	}
+}