Feature: Allow `minLines` in `SelectableText` (#50750)

* Feature: allow minLines in SelectableText

packages/flutter/lib/src/material/selectable_text.dart

@@ -205,6 +205,7 @@ class SelectableText extends StatefulWidget {
     this.showCursor = false,
     this.autofocus = false,
     ToolbarOptions toolbarOptions,
+    this.minLines,
     this.maxLines,
     this.cursorWidth = 2.0,
     this.cursorRadius,
@@ -218,6 +219,11 @@ class SelectableText extends StatefulWidget {
         assert(autofocus != null),
         assert(dragStartBehavior != null),
         assert(maxLines == null || maxLines > 0),
+        assert(minLines == null || minLines > 0),
+        assert(
+          (maxLines == null) || (minLines == null) || (maxLines >= minLines),
+          'minLines can\'t be greater than maxLines',
+        ),
         assert(
           data != null,
           'A non-null String must be provided to a SelectableText widget.',
@@ -248,6 +254,7 @@ class SelectableText extends StatefulWidget {
     this.showCursor = false,
     this.autofocus = false,
     ToolbarOptions toolbarOptions,
+    this.minLines,
     this.maxLines,
     this.cursorWidth = 2.0,
     this.cursorRadius,
@@ -261,6 +268,11 @@ class SelectableText extends StatefulWidget {
     assert(autofocus != null),
     assert(dragStartBehavior != null),
     assert(maxLines == null || maxLines > 0),
+    assert(minLines == null || minLines > 0),
+    assert(
+      (maxLines == null) || (minLines == null) || (maxLines >= minLines),
+      'minLines can\'t be greater than maxLines',
+    ),
     assert(
       textSpan != null,
       'A non-null TextSpan must be provided to a SelectableText.rich widget.',
@@ -329,6 +341,9 @@ class SelectableText extends StatefulWidget {
   /// {@macro flutter.widgets.editableText.autofocus}
   final bool autofocus;
 
+  /// {@macro flutter.widgets.editableText.minLines}
+  final int minLines;
+
   /// {@macro flutter.widgets.editableText.maxLines}
   final int maxLines;
 
@@ -398,6 +413,7 @@ class SelectableText extends StatefulWidget {
     properties.add(DiagnosticsProperty<TextStyle>('style', style, defaultValue: null));
     properties.add(DiagnosticsProperty<bool>('autofocus', autofocus, defaultValue: false));
     properties.add(DiagnosticsProperty<bool>('showCursor', showCursor, defaultValue: false));
+    properties.add(IntProperty('minLines', minLines, defaultValue: null));
     properties.add(IntProperty('maxLines', maxLines, defaultValue: null));
     properties.add(EnumProperty<TextAlign>('textAlign', textAlign, defaultValue: null));
     properties.add(EnumProperty<TextDirection>('textDirection', textDirection, defaultValue: null));
@@ -582,6 +598,7 @@ class _SelectableTextState extends State<SelectableText> with AutomaticKeepAlive
         autofocus: widget.autofocus,
         forceLine: false,
         toolbarOptions: widget.toolbarOptions,
+        minLines: widget.minLines,
         maxLines: widget.maxLines ?? defaultTextStyle.maxLines,
         selectionColor: themeData.textSelectionColor,
         selectionControls: widget.selectionEnabled ? textSelectionControls : null,

packages/flutter/test/widgets/selectable_text_test.dart

@@ -177,12 +177,17 @@ void main() {
     debugResetSemanticsIdCounter();
   });
 
-  Widget selectableTextBuilder({String text = '', int maxLines = 1}) {
+  Widget selectableTextBuilder({
+    String text = '',
+    int maxLines = 1,
+    int minLines,
+  }) {
     return boilerplate(
       child: SelectableText(
         text,
         style: const TextStyle(color: Colors.black, fontSize: 34.0),
         maxLines: maxLines,
+        minLines: minLines,
       ),
     );
   }
@@ -1155,6 +1160,41 @@ void main() {
     expect(inputBox.hitTest(BoxHitTestResult(), position: inputBox.globalToLocal(newFourthPos)), isFalse);
   });
 
+  testWidgets('minLines cannot be greater than maxLines', (WidgetTester tester) async {
+    try {
+      await tester.pumpWidget(
+        overlay(
+          child: Container(
+            width: 300.0,
+            child: SelectableText(
+              'abcd',
+              minLines: 4,
+              maxLines: 3,
+            ),
+          ),
+        ),
+      );
+    } on AssertionError catch (e) {
+      expect(e.toString(), contains("minLines can't be greater than maxLines"));
+      return;
+    }
+    fail('An assert should be triggered when minLines is greater than maxLines');
+  });
+
+  testWidgets('Selectable height with minLine', (WidgetTester tester) async {
+    await tester.pumpWidget(selectableTextBuilder());
+
+    RenderBox findTextBox() => tester.renderObject(find.byType(SelectableText));
+
+    final RenderBox textBox = findTextBox();
+    final Size emptyInputSize = textBox.size;
+
+    // Even if the text is a one liner, minimum height of SelectableText will determined by minLines
+    await tester.pumpWidget(selectableTextBuilder(text: 'No wrapping here.', minLines: 2, maxLines: 3));
+    expect(findTextBox(), equals(textBox));
+    expect(textBox.size.height, emptyInputSize.height * 2);
+  });
+
   testWidgets('Can align to center', (WidgetTester tester) async {
     await tester.pumpWidget(
       overlay(
@@ -3189,6 +3229,7 @@ void main() {
       textScaleFactor: 1.0,
       autofocus: true,
       showCursor: true,
+      minLines: 2,
       maxLines: 10,
       cursorWidth: 1.0,
       cursorRadius: Radius.zero,
@@ -3206,6 +3247,7 @@ void main() {
       'style: TextStyle(inherit: true, color: Color(0xff00ff00))',
       'autofocus: true',
       'showCursor: true',
+      'minLines: 2',
       'maxLines: 10',
       'textAlign: end',
       'textDirection: ltr',