Default to the status table output

For smart terminals, default to using the status table, using 1/4 of the
terminal height (with a min of 1 and a max of 10).

This behavior can still be overriden to a specific height with
SOONG_UI_TABLE_HEIGHT, and turned off by setting SOONG_UI_TABLE_HEIGHT
to 0.

Test: m   <adjust terminal height, see it shrink when it gets too short>
Test: SOONG_UI_TABLE_HEIGHT=20 m
Test: SOONG_UI_TABLE_HEIGHT=0 m
Change-Id: I224348a29a6e07f168c92cf5514a94bd27e32618

ui/terminal/smart_status.go

@@ -59,21 +59,24 @@ type smartStatusOutput struct {
 // current build status similarly to Ninja's built-in terminal
 // output.
 func NewSmartStatusOutput(w io.Writer, formatter formatter) status.StatusOutput {
-	tableHeight, _ := strconv.Atoi(os.Getenv(tableHeightEnVar))
-
 	s := &smartStatusOutput{
 		writer:    w,
 		formatter: formatter,
 
 		haveBlankLine: true,
 
-		tableMode:            tableHeight > 0,
-		requestedTableHeight: tableHeight,
+		tableMode: true,
 
 		done:     make(chan bool),
 		sigwinch: make(chan os.Signal),
 	}
 
+	if env, ok := os.LookupEnv(tableHeightEnVar); ok {
+		h, _ := strconv.Atoi(env)
+		s.tableMode = h > 0
+		s.requestedTableHeight = h
+	}
+
 	s.updateTermSize()
 
 	if s.tableMode {
@@ -297,6 +300,14 @@ func (s *smartStatusOutput) updateTermSize() {
 
 		if s.tableMode {
 			tableHeight := s.requestedTableHeight
+			if tableHeight == 0 {
+				tableHeight = s.termHeight / 4
+				if tableHeight < 1 {
+					tableHeight = 1
+				} else if tableHeight > 10 {
+					tableHeight = 10
+				}
+			}
 			if tableHeight > s.termHeight-1 {
 				tableHeight = s.termHeight - 1
 			}