Reduce Flickering Text

internal/completion/display.go

@@ -15,8 +15,6 @@ import (
 func Display(eng *Engine, maxRows int) {
 	eng.usedY = 0
 
-	defer fmt.Print(term.ClearScreenBelow)
-
 	// The completion engine might be inactive but still having
 	// a non-empty list of completions. This is on purpose, as
 	// sometimes it's better to keep completions printed for a

internal/completion/engine.go

@@ -288,6 +288,16 @@ func (e *Engine) Matches() int {
 	return comps
 }
 
+// DisplaySkipped reports whether completion display is suppressed.
+func (e *Engine) DisplaySkipped() bool {
+	return e.skipDisplay
+}
+
+// ResetUsedRows clears the cached displayed row count.
+func (e *Engine) ResetUsedRows() {
+	e.usedY = 0
+}
+
 // Line returns the relevant input line at the time this function is called:
 // if a candidate is currently selected, the line returned is the one containing
 // the candidate. If no candidate is selected, the normal input line is returned.

internal/display/engine.go

@@ -92,9 +92,13 @@ func (e *Engine) Refresh() {
 
 	// Display hints and completions, go back
 	// to the start of the line, then to cursor.
-	e.displayHelpers()
-	e.cursorHintToLineStart()
-	e.lineStartToCursorPos()
+	helpersMoved := e.displayHelpers()
+	if helpersMoved {
+		e.cursorHintToLineStart()
+		e.lineStartToCursorPos()
+	} else {
+		e.lineEndToCursorPos()
+	}
 	fmt.Print(term.ShowCursor)
 }
 
@@ -294,22 +298,55 @@ func (e *Engine) displayMultilinePrompts() {
 // displayHelpers renders the hint and completion sections.
 // It assumes that the cursor is on the last line of input,
 // and goes back to this same line after displaying this.
-func (e *Engine) displayHelpers() {
-	fmt.Print(term.NewlineReturn)
-
+func (e *Engine) displayHelpers() bool {
 	// Recompute completions and hints if autocompletion is on.
 	e.completer.Autocomplete()
 
+	hintRows := ui.CoordinatesHint(e.hint)
+	compMatches := e.completer.Matches()
+	compSkip := e.completer.DisplaySkipped()
+
+	if e.hintRows == 0 && e.compRows == 0 && hintRows == 0 && (compMatches == 0 || compSkip) {
+		return false
+	}
+
+	fmt.Print(term.NewlineReturn)
+
+	prevHintRows := e.hintRows
+	prevCompRows := e.compRows
+
 	// Display hint and completions.
 	ui.DisplayHint(e.hint)
 	e.hintRows = ui.CoordinatesHint(e.hint)
-	completion.Display(e.completer, e.AvailableHelperLines())
-	e.compRows = completion.Coordinates(e.completer)
+	if compMatches > 0 && !compSkip {
+		completion.Display(e.completer, e.AvailableHelperLines())
+		e.compRows = completion.Coordinates(e.completer)
+	} else {
+		e.completer.ResetUsedRows()
+		e.compRows = 0
+	}
+
+	if e.hintRows+e.compRows < prevHintRows+prevCompRows {
+		fmt.Print(term.ClearScreenBelow)
+	}
 
 	// Go back to the first line below the input line.
 	term.MoveCursorBackwards(term.GetWidth())
 	term.MoveCursorUp(e.compRows)
-	term.MoveCursorUp(ui.CoordinatesHint(e.hint))
+	term.MoveCursorUp(e.hintRows)
+
+	return true
+}
+
+// lineEndToCursorPos moves the cursor from the end of the input line
+// to the current cursor position.
+func (e *Engine) lineEndToCursorPos() {
+	if e.lineRows > e.cursorRow {
+		term.MoveCursorUp(e.lineRows - e.cursorRow)
+	}
+
+	term.MoveCursorBackwards(term.GetWidth())
+	term.MoveCursorForwards(e.cursorCol)
 }
 
 // AvailableHelperLines returns the number of lines available below the hint section.