RenderEditable WidgetSpan intrinsics (#136979)

Update the `RenderEditable` implementation to match `RenderParagraph`. Fixes https://github.com/flutter/flutter/issues/136596

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

@@ -1817,12 +1817,28 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin,
 
   @override
   double computeMinIntrinsicWidth(double height) {
+    if (!_canComputeIntrinsics) {
+      return 0.0;
+    }
+    _textPainter.setPlaceholderDimensions(layoutInlineChildren(
+      double.infinity,
+      (RenderBox child, BoxConstraints constraints) => Size(child.getMinIntrinsicWidth(double.infinity), 0.0),
+    ));
     _layoutText();
     return _textPainter.minIntrinsicWidth;
   }
 
   @override
   double computeMaxIntrinsicWidth(double height) {
+    if (!_canComputeIntrinsics) {
+      return 0.0;
+    }
+    _textPainter.setPlaceholderDimensions(layoutInlineChildren(
+      double.infinity,
+      // Height and baseline is irrelevant as all text will be laid
+      // out in a single line. Therefore, using 0.0 as a dummy for the height.
+      (RenderBox child, BoxConstraints constraints) => Size(child.getMaxIntrinsicWidth(double.infinity), 0.0),
+    ));
     _layoutText();
     return _textPainter.maxIntrinsicWidth + _caretMargin;
   }
@@ -1890,12 +1906,14 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin,
   }
 
   @override
-  double computeMinIntrinsicHeight(double width) {
-    return _preferredHeight(width);
-  }
+  double computeMinIntrinsicHeight(double width) => computeMaxIntrinsicHeight(width);
 
   @override
   double computeMaxIntrinsicHeight(double width) {
+    if (!_canComputeIntrinsics) {
+      return 0.0;
+    }
+    _textPainter.setPlaceholderDimensions(layoutInlineChildren(width, ChildLayoutHelper.dryLayoutChild));
     return _preferredHeight(width);
   }
 

packages/flutter/test/rendering/editable_test.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:math' as math;
 import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
@@ -1632,7 +1633,20 @@ void main() {
         children: renderBoxes,
       );
       _applyParentData(renderBoxes, editable.text!);
+      // Intrinsics can be computed without doing layout.
+      expect(editable.computeMaxIntrinsicWidth(fixedHeight),
+        2.0 * 10.0 * 4 + 14.0 * 7 + 1.0,
+        reason: "intrinsic width = scale factor * width of 'test' + width of 'one two' + _caretMargin",
+      );
+      expect(editable.computeMinIntrinsicWidth(fixedHeight),
+        math.max(math.max(2.0 * 10.0 * 4, 14.0 * 3), 14.0 * 3),
+        reason: "intrinsic width = max(scale factor * width of 'test', width of 'one', width of 'two')",
+      );
+      expect(editable.computeMaxIntrinsicHeight(fixedHeight), 40.0);
+      expect(editable.computeMinIntrinsicHeight(fixedHeight), 40.0);
+
       layout(editable, constraints: const BoxConstraints(maxWidth: screenWidth));
+      // Intrinsics can be computed after layout.
       expect(editable.computeMaxIntrinsicWidth(fixedHeight),
         2.0 * 10.0 * 4 + 14.0 * 7 + 1.0,
         reason: "intrinsic width = scale factor * width of 'test' + width of 'one two' + _caretMargin",