Merge branch 'johan/follow'

Fixes #108

README.md

@@ -30,6 +30,7 @@ Doing the right thing includes:
 - The position in the file is always shown
 - Supports **word wrapping** (on actual word boundaries) if requested using
   `--wrap` or by pressing <kbd>w</kbd>
+- **Follows output** as long as you are on the last line, just like `tail -f`
 
 [For compatibility reasons](https://github.com/walles/moar/issues/14), `moar`
 uses the formats declared in these environment variables when viewing man pages:

m/pager.go

@@ -55,6 +55,7 @@ type Pager struct {
 	searchString   string
 	searchPattern  *regexp.Regexp
 	gotoLineString string
+	Following      bool
 
 	isShowingHelp bool
 	preHelpState  *_PreHelpState
@@ -82,6 +83,7 @@ type _PreHelpState struct {
 	reader              *Reader
 	scrollPosition      scrollPosition
 	leftColumnZeroBased int
+	following           bool
 }
 
 const _EofMarkerFormat = "\x1b[7m" // Reverse video
@@ -133,6 +135,10 @@ Source Code
 Available at https://github.com/walles/moar/.
 `)
 
+func (pm _PagerMode) isViewing() bool {
+	return pm == _Viewing || pm == _NotFound
+}
+
 // NewPager creates a new Pager
 func NewPager(r *Reader) *Pager {
 	var name string
@@ -189,6 +195,7 @@ func (p *Pager) Quit() {
 	p.reader = p.preHelpState.reader
 	p.scrollPosition = p.preHelpState.scrollPosition
 	p.leftColumnZeroBased = p.preHelpState.leftColumnZeroBased
+	p.Following = p.preHelpState.following
 	p.preHelpState = nil
 }
 
@@ -211,6 +218,14 @@ func (p *Pager) moveRight(delta int) {
 	}
 }
 
+func (p *Pager) handleScrolledUp() {
+	p.Following = false
+}
+
+func (p *Pager) handleScrolledDown() {
+	p.Following = p.isScrolledToEnd()
+}
+
 func (p *Pager) onKey(keyCode twin.KeyCode) {
 	if p.mode == _Searching {
 		p.onSearchKey(keyCode)
@@ -234,10 +249,12 @@ func (p *Pager) onKey(keyCode twin.KeyCode) {
 	case twin.KeyUp:
 		// Clipping is done in _Redraw()
 		p.scrollPosition = p.scrollPosition.PreviousLine(1)
+		p.handleScrolledUp()
 
 	case twin.KeyDown, twin.KeyEnter:
 		// Clipping is done in _Redraw()
 		p.scrollPosition = p.scrollPosition.NextLine(1)
+		p.handleScrolledDown()
 
 	case twin.KeyRight:
 		p.moveRight(16)
@@ -247,17 +264,20 @@ func (p *Pager) onKey(keyCode twin.KeyCode) {
 
 	case twin.KeyHome:
 		p.scrollPosition = newScrollPosition("Pager scroll position")
+		p.handleScrolledUp()
 
 	case twin.KeyEnd:
 		p.scrollToEnd()
 
-	case twin.KeyPgDown:
-		_, height := p.screen.Size()
-		p.scrollPosition = p.scrollPosition.NextLine(height - 1)
-
 	case twin.KeyPgUp:
 		_, height := p.screen.Size()
 		p.scrollPosition = p.scrollPosition.PreviousLine(height - 1)
+		p.handleScrolledUp()
+
+	case twin.KeyPgDown:
+		_, height := p.screen.Size()
+		p.scrollPosition = p.scrollPosition.NextLine(height - 1)
+		p.handleScrolledDown()
 
 	default:
 		log.Debugf("Unhandled key event %v", keyCode)
@@ -287,10 +307,12 @@ func (p *Pager) onRune(char rune) {
 				reader:              p.reader,
 				scrollPosition:      p.scrollPosition,
 				leftColumnZeroBased: p.leftColumnZeroBased,
+				following:           p.Following,
 			}
 			p.reader = _HelpReader
 			p.scrollPosition = newScrollPosition("Pager scroll position")
 			p.leftColumnZeroBased = 0
+			p.Following = false
 			p.isShowingHelp = true
 		}
 
@@ -300,10 +322,12 @@ func (p *Pager) onRune(char rune) {
 	case 'k', 'y':
 		// Clipping is done in _Redraw()
 		p.scrollPosition = p.scrollPosition.PreviousLine(1)
+		p.handleScrolledUp()
 
 	case 'j', 'e':
 		// Clipping is done in _Redraw()
 		p.scrollPosition = p.scrollPosition.NextLine(1)
+		p.handleScrolledDown()
 
 	case 'l':
 		// vim right
@@ -315,6 +339,7 @@ func (p *Pager) onRune(char rune) {
 
 	case '<':
 		p.scrollPosition = newScrollPosition("Pager scroll position")
+		p.handleScrolledUp()
 
 	case '>', 'G':
 		p.scrollToEnd()
@@ -322,22 +347,26 @@ func (p *Pager) onRune(char rune) {
 	case 'f', ' ':
 		_, height := p.screen.Size()
 		p.scrollPosition = p.scrollPosition.NextLine(height - 1)
+		p.handleScrolledDown()
 
 	case 'b':
 		_, height := p.screen.Size()
 		p.scrollPosition = p.scrollPosition.PreviousLine(height - 1)
+		p.handleScrolledUp()
 
 	// '\x15' = CTRL-u, should work like just 'u'.
 	// Ref: https://github.com/walles/moar/issues/90
 	case 'u', '\x15':
 		_, height := p.screen.Size()
 		p.scrollPosition = p.scrollPosition.PreviousLine(height / 2)
+		p.handleScrolledUp()
 
 	// '\x04' = CTRL-d, should work like just 'd'.
 	// Ref: https://github.com/walles/moar/issues/90
 	case 'd', '\x04':
 		_, height := p.screen.Size()
 		p.scrollPosition = p.scrollPosition.NextLine(height / 2)
+		p.handleScrolledDown()
 
 	case '/':
 		p.mode = _Searching
@@ -458,8 +487,9 @@ func (p *Pager) StartPaging(screen twin.Screen) {
 			// We'll be implicitly redrawn just by taking another lap in the loop
 
 		case eventMoreLinesAvailable:
-			// Doing nothing here is fine; screen will be refreshed on the next
-			// iteration of the main loop.
+			if p.mode.isViewing() && p.Following {
+				p.scrollToEnd()
+			}
 
 		case eventSpinnerUpdate:
 			spinner = event.spinner

m/scrollPosition.go

@@ -277,6 +277,8 @@ func (p *Pager) scrollToEnd() {
 	// Scroll down enough. We know for sure the last line won't wrap into more
 	// lines than the number of characters it contains.
 	p.scrollPosition.internalDontTouch.deltaScreenLines = len(lastInputLine.raw)
+
+	p.Following = true
 }
 
 // Can be either because Pager.scrollToEnd() was just called or because the user

m/search.go

@@ -115,6 +115,9 @@ func (p *Pager) scrollToNextSearchHit() {
 		return
 	}
 	p.scrollPosition = *firstHitPosition
+
+	// Don't let any search hit scroll out of sight
+	p.Following = false
 }
 
 func (p *Pager) scrollToPreviousSearchHit() {
@@ -150,6 +153,9 @@ func (p *Pager) scrollToPreviousSearchHit() {
 		return
 	}
 	p.scrollPosition = *firstHitPosition
+
+	// Don't let any search hit scroll out of sight
+	p.Following = false
 }
 
 func (p *Pager) updateSearchPattern() {