Make box last line linefeed optional

There are scenarios where the box takes up the whole terminal height. In those
use cases, the linefeed at the last line takes away the possibility to use the
full terminal.

Make the linefeed at the last line configurable by introducing a box style
function called `NoFinalEndOfLine`. By default, a linefeed is added.

Author: HeavyWombat

box.go

@@ -35,9 +35,10 @@ import (
 type BoxStyle func(*boxOptions)
 
 type boxOptions struct {
-	headlineColor  *colorful.Color
-	contentColor   *colorful.Color
-	headlineStyles []bunt.StyleOption
+	headlineColor      *colorful.Color
+	contentColor       *colorful.Color
+	headlineStyles     []bunt.StyleOption
+	noClosingEndOfLine bool
 }
 
 // HeadlineColor sets the color of the headline text
@@ -61,6 +62,13 @@ func ContentColor(color colorful.Color) BoxStyle {
 	}
 }
 
+// NoFinalEndOfLine specifies that the rendering does not add a closing linefeed
+func NoFinalEndOfLine() BoxStyle {
+	return func(options *boxOptions) {
+		options.noClosingEndOfLine = true
+	}
+}
+
 // ContentBox creates a string for the terminal where content is printed inside
 // a simple box shape.
 func ContentBox(headline string, content string, opts ...BoxStyle) string {
@@ -120,6 +128,11 @@ func Box(out io.Writer, headline string, content io.Reader, opts ...BoxStyle) {
 	}
 
 	if linewritten {
-		outprint("%s\n", lastline)
+		outprint(lastline)
+
+		// If not configured otherwise, end with a linefeed
+		if !options.noClosingEndOfLine {
+			outprint("\n")
+		}
 	}
 }

box_test.go

@@ -123,6 +123,19 @@ DodgerBlue{│} DimGray{content}
 DodgerBlue{╵}
 `)))
 		})
+
+		It("should create a content box with no trailing line feed", func() {
+			Expect("\n" + ContentBox(
+				headline,
+				content,
+				NoFinalEndOfLine(),
+			)).To(BeEquivalentTo(Sprintf(`
+╭ headline
+│ multi
+│ line
+│ content
+╵`)))
+		})
 	})
 
 	Context("rendering content boxes with already colored content", func() {