Introduce ParagraphBoundary subclass for text editing (#116549)

* attempt to extend to paragraph

* second attempt

* clean up implementation

* clean up

* updates

* updates

* Fix implementation

* remove old

* update docs

* update docs

* fix analyzer

* Fix bug where new line character was selected and backwards selection failed

* remove print

* Add test for paragraph boundary

* Add text editing test for extending selection to paragraph for mac and ios

* rename to ExtendSelectionToParagraphBoundaryIntent

* fix analyzer

* Should default to downstream when collapsing selection

* get rid of _getParagraphAtOffset and move into getTextBoundaryAt

* Search for all line terminators

* iterate through code units instead of characters

* Address some reviewer comments"

* Add separate implementations for leading and trailing paragraph boundary methods

* Do not break after a carriage return if it is followed by a line feed

* test carriage return followed by a line feed

* more tests

* Do not continue if the line terminator is at the target text offset

* add hack to extend highlight to line terminator

* Revert "add hack to extend highlight to line terminator"

This reverts commit b4d3c434539b66c3c81c215e87c645b425902825.

* Revert "Do not continue if the line terminator is at the target text offset"

This reverts commit 789e1b838e54e7c25600bfa8852e59431ccaf5dc.

* Update ParagraphBoundary with latest TextBoundary changes

* Update implementation to iterate through indexes

* update getTrailingTextBoundaryAt to include the line terminator

* Updates

* more updates

* more updates

* updates

* updates

* Lets try this again

* clean up

* updates

* more updates

* updates

* fix

* Re-implement using custom paragraph boundary applying method

* Revert "Re-implement using custom paragraph boundary applying method"

This reverts commit cd2f7f4b6eb6726b28f82a43708812e06a49df95.

* Revert "fix"

This reverts commit 8ec1f8f58935cfb3eb86dc6afd2894537af4cf7b.

* updates

* Revert "updates"

This reverts commit 9dcca4a0031fe18ada9d6ffbbe77ba09918e82ae.

* Revert "Revert "fix""

This reverts commit 9cc1332cd3041badc472d0d223a106203e46afb8.

* Revert "Revert "Re-implement using custom paragraph boundary applying method""

This reverts commit 1acb606fb743fd840da20cca26d9a7c26accb71d.

* Fix paragraph boundaries

* Add failing test

* Address some comments

* group tests and fix analyzer

* fix typo

* fix remaining test

* updates

* more fixes and logs

* clean up and add another test

* Fix last test

* Add new test

* Clean up

* more clean up

* clean up comments

* address comments

* updates

* return null when position is out of bounds and 0 or end of text if appropriate

* Clean up cases

* Do not return null when OOB in the direction of iteration

* clean up

* simplify implementation thanks to LongCatIsLooong feedback

* Address comments

* Add line and paragraph separator

* Use _moveBeyondTextBoundary instead of custom _moveToParagraphBoundary

* Change some intent names and revert fromPosition change

* clean up docs

---------

Co-authored-by: Renzo Olivares <roliv@google.com>

Author: Renzo-Olivares

packages/flutter/lib/src/services/text_boundary.dart

@@ -123,9 +123,87 @@ class LineBoundary extends TextBoundary {
   TextRange getTextBoundaryAt(int position) => _textLayout.getLineAtOffset(TextPosition(offset: max(position, 0)));
 }
 
+/// A text boundary that uses paragraphs as logical boundaries.
+///
+/// A paragraph is defined as the range between line terminators. If no
+/// line terminators exist then the paragraph boundary is the entire document.
+class ParagraphBoundary extends TextBoundary {
+  /// Creates a [ParagraphBoundary] with the text.
+  const ParagraphBoundary(this._text);
+
+  final String _text;
+
+  /// Returns the [int] representing the start position of the paragraph that
+  /// bounds the given `position`. The returned [int] is the position of the code unit
+  /// that follows the line terminator that encloses the desired paragraph.
+  @override
+  int? getLeadingTextBoundaryAt(int position) {
+    if (position < 0 || _text.isEmpty) {
+      return null;
+    }
+
+    if (position >= _text.length) {
+      return _text.length;
+    }
+
+    if (position == 0) {
+      return 0;
+    }
+
+    final List<int> codeUnits = _text.codeUnits;
+    int index = position;
+
+    if (index > 1 && codeUnits[index] == 0xA && codeUnits[index - 1] == 0xD) {
+      index -= 2;
+    } else if (TextLayoutMetrics.isLineTerminator(codeUnits[index])) {
+      index -= 1;
+    }
+
+    while (index > 0) {
+      if (TextLayoutMetrics.isLineTerminator(codeUnits[index])) {
+        return index + 1;
+      }
+      index -= 1;
+    }
+
+    return max(index, 0);
+  }
+
+  /// Returns the [int] representing the end position of the paragraph that
+  /// bounds the given `position`. The returned [int] is the position of the
+  /// code unit representing the trailing line terminator that encloses the
+  /// desired paragraph.
+  @override
+  int? getTrailingTextBoundaryAt(int position) {
+    if (position >= _text.length || _text.isEmpty) {
+      return null;
+    }
+
+    if (position < 0) {
+      return 0;
+    }
+
+    final List<int> codeUnits = _text.codeUnits;
+    int index = position;
+
+    while (!TextLayoutMetrics.isLineTerminator(codeUnits[index])) {
+      index += 1;
+      if (index == codeUnits.length) {
+        return index;
+      }
+    }
+
+    return index < codeUnits.length - 1
+                && codeUnits[index] == 0xD
+                && codeUnits[index + 1] == 0xA
+                ? index + 2
+                : index + 1;
+  }
+}
+
 /// A text boundary that uses the entire document as logical boundary.
 class DocumentBoundary extends TextBoundary {
-  /// Creates a [DocumentBoundary] with the text
+  /// Creates a [DocumentBoundary] with the text.
   const DocumentBoundary(this._text);
 
   final String _text;

packages/flutter/lib/src/services/text_layout_metrics.dart

@@ -54,6 +54,25 @@ abstract class TextLayoutMetrics {
     return true;
   }
 
+  /// Check if the given code unit is a line terminator character.
+  ///
+  /// Includes newline characters from ASCII
+  /// (https://www.unicode.org/standard/reports/tr13/tr13-5.html).
+  static bool isLineTerminator(int codeUnit) {
+    switch (codeUnit) {
+      case 0xA: // line feed
+      case 0xB: // vertical feed
+      case 0xC: // form feed
+      case 0xD: // carriage return
+      case 0x85: // new line
+      case 0x2028: // line separator
+      case 0x2029: // paragraph separator
+        return true;
+      default:
+        return false;
+    }
+  }
+
   /// {@template flutter.services.TextLayoutMetrics.getLineAtOffset}
   /// Return a [TextSelection] containing the line of the given [TextPosition].
   /// {@endtemplate}

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

@@ -303,8 +303,8 @@ class DefaultTextEditingShortcuts extends StatelessWidget {
 
     const SingleActivator(LogicalKeyboardKey.arrowLeft, shift: true, alt: true): const ExtendSelectionToNextWordBoundaryOrCaretLocationIntent(forward: false),
     const SingleActivator(LogicalKeyboardKey.arrowRight, shift: true, alt: true): const ExtendSelectionToNextWordBoundaryOrCaretLocationIntent(forward: true),
-    const SingleActivator(LogicalKeyboardKey.arrowUp, shift: true, alt: true): const ExtendSelectionVerticallyToAdjacentLineIntent(forward: false, collapseSelection: false),
-    const SingleActivator(LogicalKeyboardKey.arrowDown, shift: true, alt: true): const ExtendSelectionVerticallyToAdjacentLineIntent(forward: true, collapseSelection: false),
+    const SingleActivator(LogicalKeyboardKey.arrowUp, shift: true, alt: true): const ExtendSelectionToNextParagraphBoundaryOrCaretLocationIntent(forward: false),
+    const SingleActivator(LogicalKeyboardKey.arrowDown, shift: true, alt: true): const ExtendSelectionToNextParagraphBoundaryOrCaretLocationIntent(forward: true),
 
     const SingleActivator(LogicalKeyboardKey.arrowLeft, meta: true): const ExtendSelectionToLineBreakIntent(forward: false, collapseSelection: true),
     const SingleActivator(LogicalKeyboardKey.arrowRight, meta: true): const ExtendSelectionToLineBreakIntent(forward: true, collapseSelection: true),
@@ -560,8 +560,8 @@ Intent? intentForMacOSSelector(String selectorName) {
 
     'moveWordLeftAndModifySelection:': ExtendSelectionToNextWordBoundaryOrCaretLocationIntent(forward: false),
     'moveWordRightAndModifySelection:': ExtendSelectionToNextWordBoundaryOrCaretLocationIntent(forward: true),
-    'moveParagraphBackwardAndModifySelection:': ExtendSelectionToLineBreakIntent(forward: false, collapseSelection: false, collapseAtReversal: true),
-    'moveParagraphForwardAndModifySelection:': ExtendSelectionToLineBreakIntent(forward: true, collapseSelection: false, collapseAtReversal: true),
+    'moveParagraphBackwardAndModifySelection:': ExtendSelectionToNextParagraphBoundaryOrCaretLocationIntent(forward: false),
+    'moveParagraphForwardAndModifySelection:': ExtendSelectionToNextParagraphBoundaryOrCaretLocationIntent(forward: true),
 
     'moveToLeftEndOfLine:': ExtendSelectionToLineBreakIntent(forward: false, collapseSelection: true),
     'moveToRightEndOfLine:': ExtendSelectionToLineBreakIntent(forward: true, collapseSelection: true),

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

@@ -3978,6 +3978,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
   TextBoundary _characterBoundary() => widget.obscureText ? _CodeUnitBoundary(_value.text) : CharacterBoundary(_value.text);
   TextBoundary _nextWordBoundary() => widget.obscureText ? _documentBoundary() : renderEditable.wordBoundaries.moveByWordBoundary;
   TextBoundary _linebreak() => widget.obscureText ? _documentBoundary() : LineBoundary(renderEditable);
+  TextBoundary _paragraphBoundary() => ParagraphBoundary(_value.text);
   TextBoundary _documentBoundary() => DocumentBoundary(_value.text);
 
   Action<T> _makeOverridable<T extends Intent>(Action<T> defaultAction) {
@@ -4218,6 +4219,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
     ExtendSelectionToLineBreakIntent: _makeOverridable(_UpdateTextSelectionAction<ExtendSelectionToLineBreakIntent>(this, _linebreak, _moveToTextBoundary, ignoreNonCollapsedSelection: true)),
     ExtendSelectionVerticallyToAdjacentLineIntent: _makeOverridable(_verticalSelectionUpdateAction),
     ExtendSelectionVerticallyToAdjacentPageIntent: _makeOverridable(_verticalSelectionUpdateAction),
+    ExtendSelectionToNextParagraphBoundaryOrCaretLocationIntent: _makeOverridable(_UpdateTextSelectionAction<ExtendSelectionToNextParagraphBoundaryOrCaretLocationIntent>(this, _paragraphBoundary, _moveBeyondTextBoundary, ignoreNonCollapsedSelection: true)),
     ExtendSelectionToDocumentBoundaryIntent: _makeOverridable(_UpdateTextSelectionAction<ExtendSelectionToDocumentBoundaryIntent>(this, _documentBoundary, _moveBeyondTextBoundary, ignoreNonCollapsedSelection: true)),
     ExtendSelectionToNextWordBoundaryOrCaretLocationIntent: _makeOverridable(_UpdateTextSelectionAction<ExtendSelectionToNextWordBoundaryOrCaretLocationIntent>(this, _nextWordBoundary, _moveBeyondTextBoundary, ignoreNonCollapsedSelection: true)),
     ScrollToDocumentBoundaryIntent: _makeOverridable(CallbackAction<ScrollToDocumentBoundaryIntent>(onInvoke: _scrollToDocumentBoundary)),

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

@@ -221,6 +221,21 @@ class ExtendSelectionVerticallyToAdjacentPageIntent extends DirectionalCaretMove
   }) : super(forward, collapseSelection);
 }
 
+/// Extends, or moves the current selection from the current
+/// [TextSelection.extent] position to the previous or the next paragraph
+/// boundary depending on the [forward] parameter.
+///
+/// This [Intent] collapses the selection when the order of [TextSelection.base]
+/// and [TextSelection.extent] would reverse.
+///
+/// This is typically only used on MacOS.
+class ExtendSelectionToNextParagraphBoundaryOrCaretLocationIntent extends DirectionalCaretMovementIntent {
+  /// Creates an [ExtendSelectionToNextParagraphBoundaryOrCaretLocationIntent].
+  const ExtendSelectionToNextParagraphBoundaryOrCaretLocationIntent({
+    required bool forward,
+  }) : super(forward, false, true);
+}
+
 /// Extends, or moves the current selection from the current
 /// [TextSelection.extent] position to the start or the end of the document.
 ///

packages/flutter/test/services/text_boundary_test.dart

@@ -146,6 +146,113 @@ void main() {
     expect(boundary.getTextBoundaryAt(3), TestTextLayoutMetrics.lineAt3);
   });
 
+  group('paragraph boundary', () {
+    test('works for simple cases', () {
+      const String textA= 'abcd efg hi\njklmno\npqrstuv';
+      const ParagraphBoundary boundaryA = ParagraphBoundary(textA);
+
+      // Position enclosed inside of paragraph, 'abcd efg h|i\n'.
+      const int position = 10;
+
+      // The range includes the line terminator.
+      expect(boundaryA.getLeadingTextBoundaryAt(position), 0);
+      expect(boundaryA.getTrailingTextBoundaryAt(position), 12);
+
+      // This text includes a carriage return followed by a line feed.
+      const String textB = 'abcd efg hi\r\njklmno\npqrstuv';
+      const ParagraphBoundary boundaryB = ParagraphBoundary(textB);
+      expect(boundaryB.getLeadingTextBoundaryAt(position), 0);
+      expect(boundaryB.getTrailingTextBoundaryAt(position), 13);
+
+      const String textF = 'Now is the time for\n' // 20
+          'all good people\n'                         // 20 + 16 => 36
+          'to come to the aid\n'                      // 36 + 19 => 55
+          'of their country.';                        // 55 + 17 => 72
+      const ParagraphBoundary boundaryF = ParagraphBoundary(textF);
+      const int positionF = 11;
+      expect(boundaryF.getLeadingTextBoundaryAt(positionF), 0);
+      expect(boundaryF.getTrailingTextBoundaryAt(positionF), 20);
+    });
+
+    test('works for consecutive line terminators involving CRLF', () {
+      const String textI = 'Now is the time for\n' // 20
+          'all good people\n\r\n'                         // 20 + 16 => 38
+          'to come to the aid\n'                      // 38 + 19 => 57
+          'of their country.';                        // 57 + 17 => 74
+      const ParagraphBoundary boundaryI = ParagraphBoundary(textI);
+      const int positionI = 56;// \n at the end of the third line.
+      const int positionJ = 38;// t at beginning of third line.
+      const int positionK = 37;// \n at end of second line.
+      expect(boundaryI.getLeadingTextBoundaryAt(positionI), 38);
+      expect(boundaryI.getTrailingTextBoundaryAt(positionI), 57);
+      expect(boundaryI.getLeadingTextBoundaryAt(positionJ), 38);
+      expect(boundaryI.getTrailingTextBoundaryAt(positionJ), 57);
+      expect(boundaryI.getLeadingTextBoundaryAt(positionK), 36);
+      expect(boundaryI.getTrailingTextBoundaryAt(positionK), 38);
+    });
+
+    test('works for consecutive line terminators', () {
+      const String textI = 'Now is the time for\n' // 20
+          'all good people\n\n'                         // 20 + 16 => 37
+          'to come to the aid\n'                      // 37 + 19 => 56
+          'of their country.';                        // 56 + 17 => 73
+      const ParagraphBoundary boundaryI = ParagraphBoundary(textI);
+      const int positionI = 55;// \n at the end of the third line.
+      const int positionJ = 37;// t at beginning of third line.
+      const int positionK = 36;// \n at end of second line.
+      expect(boundaryI.getLeadingTextBoundaryAt(positionI), 37);
+      expect(boundaryI.getTrailingTextBoundaryAt(positionI), 56);
+      expect(boundaryI.getLeadingTextBoundaryAt(positionJ), 37);
+      expect(boundaryI.getTrailingTextBoundaryAt(positionJ), 56);
+      expect(boundaryI.getLeadingTextBoundaryAt(positionK), 36);
+      expect(boundaryI.getTrailingTextBoundaryAt(positionK), 37);
+    });
+
+    test('leading boundary works for consecutive CRLF', () {
+      // This text includes multiple consecutive carriage returns followed by line feeds (CRLF).
+      const String textH = 'abcd efg hi\r\n\r\n\r\n\r\n\r\n\r\n\r\n\n\n\n\n\njklmno\npqrstuv';
+      const ParagraphBoundary boundaryH = ParagraphBoundary(textH);
+      const int positionH = 18;
+      expect(boundaryH.getLeadingTextBoundaryAt(positionH), 17);
+      expect(boundaryH.getTrailingTextBoundaryAt(positionH), 19);
+    });
+
+    test('trailing boundary works for consecutive CRLF', () {
+      // This text includes multiple consecutive carriage returns followed by line feeds (CRLF).
+      const String textG = 'abcd efg hi\r\n\n\n\n\n\n\r\n\r\n\r\n\r\n\n\n\n\n\njklmno\npqrstuv';
+      const ParagraphBoundary boundaryG = ParagraphBoundary(textG);
+      const int positionG = 18;
+      expect(boundaryG.getLeadingTextBoundaryAt(positionG), 18);
+      expect(boundaryG.getTrailingTextBoundaryAt(positionG), 20);
+    });
+
+    test('works when position is between two CRLF', () {
+      const String textE = 'abcd efg hi\r\nhello\r\n\n';
+      const ParagraphBoundary boundaryE = ParagraphBoundary(textE);
+      // Position enclosed inside of paragraph, 'abcd efg hi\r\nhello\r\n\n'.
+      const int positionE = 16;
+      expect(boundaryE.getLeadingTextBoundaryAt(positionE), 13);
+      expect(boundaryE.getTrailingTextBoundaryAt(positionE), 20);
+    });
+
+    test('works for multiple consecutive line terminators', () {
+      // This text includes multiple consecutive line terminators.
+      const String textC = 'abcd efg hi\r\n\n\n\n\n\n\n\n\n\n\n\njklmno\npqrstuv';
+      const ParagraphBoundary boundaryC = ParagraphBoundary(textC);
+      // Position enclosed inside of paragraph, 'abcd efg hi\r\n\n\n\n\n\n|\n\n\n\n\n\njklmno\npqrstuv'.
+      const int positionC = 18;
+      expect(boundaryC.getLeadingTextBoundaryAt(positionC), 18);
+      expect(boundaryC.getTrailingTextBoundaryAt(positionC), 19);
+
+      const String textD = 'abcd efg hi\r\n\n\n\n';
+      const ParagraphBoundary boundaryD = ParagraphBoundary(textD);
+      // Position enclosed inside of paragraph, 'abcd efg hi\r\n\n|\n\n'.
+      const int positionD = 14;
+      expect(boundaryD.getLeadingTextBoundaryAt(positionD), 14);
+      expect(boundaryD.getTrailingTextBoundaryAt(positionD), 15);
+    });
+  });
+
   test('document boundary works', () {
     const String text = 'abcd efg hi\njklmno\npqrstuv';
     const DocumentBoundary boundary = DocumentBoundary(text);