From 786d0306dbd4c354f8e1f69e18580452e7308d24 Mon Sep 17 00:00:00 2001
From: Michael Goderbauer <goderbauer@google.com>
Date: Tue, 10 Nov 2020 14:29:41 -0800
Subject: [PATCH] Assert for RenderFlex intrinsics if using baseline alignment
 (#70139)

---
 packages/flutter/lib/src/rendering/flex.dart  | 10 +++++++
 .../flutter/test/rendering/flex_test.dart     | 26 +++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/packages/flutter/lib/src/rendering/flex.dart b/packages/flutter/lib/src/rendering/flex.dart
index fc4329cf60..a3a464d523 100644
--- a/packages/flutter/lib/src/rendering/flex.dart
+++ b/packages/flutter/lib/src/rendering/flex.dart
@@ -512,6 +512,16 @@ class RenderFlex extends RenderBox with ContainerRenderObjectMixin<RenderBox, Fl
     required double extent, // the extent in the direction that isn't the sizing direction
     required _ChildSizingFunction childSize, // a method to find the size in the sizing direction
   }) {
+    if (crossAxisAlignment == CrossAxisAlignment.baseline) {
+      // Intrinsics cannot be calculated without a full layout for
+      // baseline alignment. Throw an assertion and return 0.0 as documented
+      // on [RenderBox.computeMinIntrinsicWidth].
+      assert(
+        RenderObject.debugCheckingIntrinsics,
+        'Intrinsics are not available for CrossAxisAlignment.baseline.'
+      );
+      return 0.0;
+    }
     if (_direction == sizingDirection) {
       // INTRINSIC MAIN SIZE
       // Intrinsic main size is the smallest size the flex container can take
diff --git a/packages/flutter/test/rendering/flex_test.dart b/packages/flutter/test/rendering/flex_test.dart
index f49ef6bd94..3d5f2718f5 100644
--- a/packages/flutter/test/rendering/flex_test.dart
+++ b/packages/flutter/test/rendering/flex_test.dart
@@ -606,4 +606,30 @@ void main() {
     expect(box2.size, const Size(100.0, 100.0));
     expect(box3.size, const Size(100.0, 100.0));
   });
+
+  test('Intrinsics throw if alignment is baseline', () {
+    final RenderDecoratedBox box = RenderDecoratedBox(
+      decoration: const BoxDecoration(),
+    );
+    final RenderFlex flex = RenderFlex(
+      textDirection: TextDirection.ltr,
+      children: <RenderBox>[box],
+      crossAxisAlignment: CrossAxisAlignment.baseline,
+      textBaseline: TextBaseline.alphabetic,
+    );
+    layout(flex, constraints: const BoxConstraints(
+      minWidth: 200.0, maxWidth: 200.0, minHeight: 200.0, maxHeight: 200.0,
+    ));
+
+    final Matcher cannotCalculateIntrinsics = throwsA(isAssertionError.having(
+      (AssertionError e) => e.message,
+      'message',
+      'Intrinsics are not available for CrossAxisAlignment.baseline.',
+    ));
+
+    expect(() => flex.getMaxIntrinsicHeight(100), cannotCalculateIntrinsics);
+    expect(() => flex.getMinIntrinsicHeight(100), cannotCalculateIntrinsics);
+    expect(() => flex.getMaxIntrinsicWidth(100), cannotCalculateIntrinsics);
+    expect(() => flex.getMinIntrinsicWidth(100), cannotCalculateIntrinsics);
+  });
 }