Add support for negative --height

fzf --height=-1

Close #3487

src/core.go

@@ -200,7 +200,7 @@ func Run(opts *Options, version string, revision string) {
 	padHeight := 0
 	heightUnknown := opts.Height.auto
 	if heightUnknown {
-		maxFit, padHeight = terminal.MaxFitAndPad(opts)
+		maxFit, padHeight = terminal.MaxFitAndPad()
 	}
 	deferred := opts.Select1 || opts.Exit0
 	go terminal.Loop()

src/options.go

@@ -57,6 +57,8 @@ const usage = `usage: fzf [options]
   Layout
     --height=[~]HEIGHT[%]  Display fzf window below the cursor with the given
                            height instead of using fullscreen.
+                           A negative value is calcalated as the terminal height
+                           minus the given value.
                            If prefixed with '~', fzf will determine the height
                            according to the input size.
     --min-height=HEIGHT    Minimum height when --height is given in percent
@@ -157,6 +159,7 @@ type heightSpec struct {
 	size    float64
 	percent bool
 	auto    bool
+	inverse bool
 }
 
 type sizeSpec struct {
@@ -1386,6 +1389,13 @@ func parseHeight(str string) heightSpec {
 		heightSpec.auto = true
 		str = str[1:]
 	}
+	if strings.HasPrefix(str, "-") {
+		if heightSpec.auto {
+			errorExit("negative(-) height is not compatible with adaptive(~) height")
+		}
+		heightSpec.inverse = true
+		str = str[1:]
+	}
 
 	size := parseSize(str, 100, "height")
 	heightSpec.size = size.size

src/terminal.go

@@ -594,10 +594,17 @@ func makeSpinner(unicode bool) []string {
 }
 
 func evaluateHeight(opts *Options, termHeight int) int {
+	size := opts.Height.size
 	if opts.Height.percent {
-		return util.Max(int(opts.Height.size*float64(termHeight)/100.0), opts.MinHeight)
+		if opts.Height.inverse {
+			size = 100 - size
+		}
+		return util.Max(int(size*float64(termHeight)/100.0), opts.MinHeight)
 	}
-	return int(opts.Height.size)
+	if opts.Height.inverse {
+		size = float64(termHeight) - size
+	}
+	return int(size)
 }
 
 // NewTerminal returns new Terminal object
@@ -819,7 +826,7 @@ func (t *Terminal) extraLines() int {
 	return extra
 }
 
-func (t *Terminal) MaxFitAndPad(opts *Options) (int, int) {
+func (t *Terminal) MaxFitAndPad() (int, int) {
 	_, screenHeight, marginInt, paddingInt := t.adjustMarginAndPadding()
 	padHeight := marginInt[0] + marginInt[2] + paddingInt[0] + paddingInt[2]
 	fit := screenHeight - padHeight - t.extraLines()