fix: subtract trailing padding in editor intrinsic size computations

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Fixed an issue where bullet points became visually detached from the text body when toggling text direction formatting (RTL) by locking the list leading block to the editor's base text direction.
 - Fixed typed text being inserted at the previous caret position on Android after moving the caret with a tap/mouse by keeping the platform IME's editing state in sync with the selection even when the keyboard is hidden.
+- Fixed the editor's intrinsic size adding the trailing padding instead of subtracting it, which made `IntrinsicHeight`/`IntrinsicWidth` measure the content at the undeflated size and overflow by one line at the exact moment a line wraps.
 
 ### Removed
 

lib/src/editor/editor.dart

@@ -1850,7 +1850,7 @@ class RenderEditableContainerBox extends RenderBox
     return _getIntrinsicCrossAxis((child) {
       final childHeight = math.max<double>(
         0,
-        height - _resolvedPadding!.top + _resolvedPadding!.bottom,
+        height - _resolvedPadding!.vertical,
       );
       return child.getMinIntrinsicWidth(childHeight) +
           _resolvedPadding!.left +
@@ -1864,7 +1864,7 @@ class RenderEditableContainerBox extends RenderBox
     return _getIntrinsicCrossAxis((child) {
       final childHeight = math.max<double>(
         0,
-        height - _resolvedPadding!.top + _resolvedPadding!.bottom,
+        height - _resolvedPadding!.vertical,
       );
       return child.getMaxIntrinsicWidth(childHeight) +
           _resolvedPadding!.left +
@@ -1878,7 +1878,7 @@ class RenderEditableContainerBox extends RenderBox
     return _getIntrinsicMainAxis((child) {
       final childWidth = math.max<double>(
         0,
-        width - _resolvedPadding!.left + _resolvedPadding!.right,
+        width - _resolvedPadding!.horizontal,
       );
       return child.getMinIntrinsicHeight(childWidth) +
           _resolvedPadding!.top +
@@ -1892,7 +1892,7 @@ class RenderEditableContainerBox extends RenderBox
     return _getIntrinsicMainAxis((child) {
       final childWidth = math.max<double>(
         0,
-        width - _resolvedPadding!.left + _resolvedPadding!.right,
+        width - _resolvedPadding!.horizontal,
       );
       return child.getMaxIntrinsicHeight(childWidth) +
           _resolvedPadding!.top +

test/bug_fix_test.dart

@@ -242,4 +242,63 @@ void main() {
       );
     },
   );
+
+  group('2748 - RenderEditableContainerBox intrinsics add trailing padding '
+      'instead of subtracting it', () {
+    testWidgets(
+      'intrinsic height matches laid-out height with horizontal padding',
+      (tester) async {
+        const editorWidth = 400.0;
+        const padding = EdgeInsets.symmetric(horizontal: 100, vertical: 10);
+
+        // Measure the test font's glyph advance, then build a single word
+        // sized to fill one full editor width: it fits on one line at the
+        // undeflated width (the buggy intrinsic measure) but must wrap once
+        // laid out at the padding-deflated width.
+        final glyphPainter = TextPainter(
+          text: const TextSpan(text: 'a', style: TextStyle(fontSize: 16)),
+          textDirection: TextDirection.ltr,
+        )..layout();
+        final word = 'a' * (editorWidth ~/ glyphPainter.width);
+
+        final controller = QuillController.basic()..document.insert(0, word);
+
+        await tester.pumpWidget(
+          QuillTestApp.withScaffold(
+            Align(
+              alignment: Alignment.topLeft,
+              child: SizedBox(
+                width: editorWidth,
+                child: QuillEditor.basic(
+                  controller: controller,
+                  config: const QuillEditorConfig(padding: padding),
+                ),
+              ),
+            ),
+          ),
+        );
+
+        final renderEditor = tester.allRenderObjects
+            .whereType<RenderEditor>()
+            .single;
+        final laidOutHeight = renderEditor.size.height;
+
+        // Guard: the word must actually wrap at the deflated width,
+        // otherwise the intrinsic and layout widths are indistinguishable.
+        expect(
+          laidOutHeight,
+          greaterThan(padding.vertical + glyphPainter.height * 1.5),
+        );
+
+        expect(
+          renderEditor.getMaxIntrinsicHeight(editorWidth),
+          moreOrLessEquals(laidOutHeight),
+        );
+        expect(
+          renderEditor.getMinIntrinsicHeight(editorWidth),
+          moreOrLessEquals(laidOutHeight),
+        );
+      },
+    );
+  });
 }