Add a maxLines parameter for multiline Input. (#6328)

If maxLines is 1, it's a single line Input that scrolls horizontally.
Otherwise, overflowed text wraps and scrolls vertically, taking up at
most `maxLines`.

Also fixed scrolling behavior so that the Input scrolls ensuring the
cursor is always visible.

Fixes https://github.com/flutter/flutter/issues/6271

packages/flutter/lib/src/rendering/editable_line.dart

@@ -184,7 +184,7 @@ class RenderEditable extends RenderBox {
     if (selection.isCollapsed) {
       // TODO(mpcomplete): This doesn't work well at an RTL/LTR boundary.
       Offset caretOffset = _textPainter.getOffsetForCaret(selection.extent, _caretPrototype);
-      Point start = new Point(0.0, constraints.constrainHeight(_preferredLineHeight)) + caretOffset + offset;
+      Point start = new Point(0.0, _preferredLineHeight) + caretOffset + offset;
       return <TextSelectionPoint>[new TextSelectionPoint(localToGlobal(start), null)];
     } else {
       List<ui.TextBox> boxes = _textPainter.getBoxesForSelection(selection);
@@ -206,10 +206,9 @@ class RenderEditable extends RenderBox {
   /// Returns the Rect in local coordinates for the caret at the given text
   /// position.
   Rect getLocalRectForCaret(TextPosition caretPosition) {
-    double lineHeight = constraints.constrainHeight(_preferredLineHeight);
     Offset caretOffset = _textPainter.getOffsetForCaret(caretPosition, _caretPrototype);
     // This rect is the same as _caretPrototype but without the vertical padding.
-    return new Rect.fromLTWH(0.0, 0.0, _kCaretWidth, lineHeight).shift(caretOffset + _paintOffset);
+    return new Rect.fromLTWH(0.0, 0.0, _kCaretWidth, _preferredLineHeight).shift(caretOffset + _paintOffset);
   }
 
   Size _contentSize;
@@ -223,7 +222,7 @@ class RenderEditable extends RenderBox {
       // TODO(abarth): ParagraphBuilder#build's argument should be optional.
       // TODO(abarth): These min/max values should be the default for ui.Paragraph.
       _layoutTemplate = builder.build(new ui.ParagraphStyle())
-        ..layout(new ui.ParagraphConstraints(width: _maxContentWidth));
+        ..layout(new ui.ParagraphConstraints(width: double.INFINITY));
     }
     return _layoutTemplate.height;
   }
@@ -241,7 +240,7 @@ class RenderEditable extends RenderBox {
 
   @override
   double computeMaxIntrinsicHeight(double width) {
-    return _preferredLineHeight;
+    return _preferredLineHeight * maxLines;
   }
 
   @override
@@ -303,12 +302,11 @@ class RenderEditable extends RenderBox {
   @override
   void performLayout() {
     Size oldSize = hasSize ? size : null;
-    double lineHeight = constraints.constrainHeight(_preferredLineHeight);
-    _caretPrototype = new Rect.fromLTWH(0.0, _kCaretHeightOffset, _kCaretWidth, lineHeight - 2.0 * _kCaretHeightOffset);
+    _caretPrototype = new Rect.fromLTWH(0.0, _kCaretHeightOffset, _kCaretWidth, _preferredLineHeight - 2.0 * _kCaretHeightOffset);
     _selectionRects = null;
     _textPainter.layout(maxWidth: _maxContentWidth);
     size = new Size(constraints.maxWidth, constraints.constrainHeight(
-      _textPainter.height.clamp(lineHeight, lineHeight * _maxLines)
+      _textPainter.height.clamp(_preferredLineHeight, _preferredLineHeight * _maxLines)
     ));
     Size contentSize = new Size(_textPainter.width + _kCaretGap + _kCaretWidth, _textPainter.height);
     assert(_selection != null);

packages/flutter/lib/src/widgets/scrollable.dart

@@ -513,6 +513,11 @@ class ScrollableState<T extends Scrollable> extends State<T> with SingleTickerPr
   /// If there are no in-progress scrolling physics, this function scrolls to
   /// the given offset instead.
   void didUpdateScrollBehavior(double newScrollOffset) {
+    _setStateMaybeDuringBuild(() {
+      _contentExtent = scrollBehavior.contentExtent;
+      _containerExtent = scrollBehavior.containerExtent;
+    });
+
     // This does not call setState, because if anything below actually
     // changes our build, it will itself independently trigger a frame.
     assert(_controller.isAnimating || _simulation == null);
@@ -536,8 +541,6 @@ class ScrollableState<T extends Scrollable> extends State<T> with SingleTickerPr
   ///     [didUpdateScrollBehavior].
   ///  3. Updating this object's gesture detector with [updateGestureDetector].
   void handleExtentsChanged(double contentExtent, double containerExtent) {
-    _contentExtent = contentExtent;
-    _containerExtent = containerExtent;
     didUpdateScrollBehavior(scrollBehavior.updateExtents(
       contentExtent: contentExtent,
       containerExtent: containerExtent,

packages/flutter/test/widget/input_test.dart

@@ -311,7 +311,7 @@ void main() {
     await gesture.moveTo(newHandlePos);
     await tester.pump();
     await gesture.up();
-    await tester.pump();
+    await tester.pumpWidget(builder());
 
     expect(inputValue.selection.baseOffset, selection.baseOffset);
     expect(inputValue.selection.extentOffset, selection.extentOffset+2);
@@ -565,7 +565,7 @@ void main() {
     await gesture.moveTo(newHandlePos);
     await tester.pump();
     await gesture.up();
-    await tester.pump();
+    await tester.pumpWidget(builder());
 
     expect(inputValue.selection.baseOffset, 76);
     expect(inputValue.selection.extentOffset, 108);
@@ -635,7 +635,11 @@ void main() {
     TestGesture gesture = await tester.startGesture(firstPos, pointer: 7);
     await tester.pump();
     await gesture.moveBy(new Offset(0.0, -1000.0));
-    await tester.pump();
+    await tester.pump(const Duration(seconds: 2));
+    // Wait and drag again to trigger https://github.com/flutter/flutter/issues/6329
+    // (No idea why this is necessary, but the bug wouldn't repro without it.)
+    await gesture.moveBy(new Offset(0.0, -1000.0));
+    await tester.pump(const Duration(seconds: 2));
     await gesture.up();
     await tester.pump();
 
@@ -679,5 +683,4 @@ void main() {
     expect(inputBox.hitTest(new HitTestResult(), position: inputBox.globalToLocal(newFirstPos)), isTrue);
     expect(inputBox.hitTest(new HitTestResult(), position: inputBox.globalToLocal(newFourthPos)), isFalse);
   });
-
 }