Provide details when reporting invalid constraints (#3281)

This also shrinks the width of the error messages a bit because now that
we use 'package:' URLs the stacks are a bit narrower.

examples/layers/rendering/src/sector_layout.dart

@@ -43,7 +43,10 @@ class SectorConstraints extends Constraints {
   bool get isNormalized => minDeltaRadius <= maxDeltaRadius && minDeltaTheta <= maxDeltaTheta;
 
   @override
-  bool debugAssertIsValid({ bool isAppliedConstraint: false }) {
+  bool debugAssertIsValid({
+    bool isAppliedConstraint: false,
+    InformationCollector informationCollector
+  }) {
     assert(isNormalized);
     return isNormalized;
   }

packages/flutter/lib/src/gestures/binding.dart

@@ -134,7 +134,7 @@ class FlutterErrorDetailsForPointerEventDispatcher extends FlutterErrorDetails {
     String context,
     this.event,
     this.hitTestEntry,
-    FlutterInformationCollector informationCollector,
+    InformationCollector informationCollector,
     bool silent: false
   }) : super(
     exception: exception,

packages/flutter/lib/src/gestures/pointer_router.dart

@@ -89,7 +89,7 @@ class FlutterErrorDetailsForPointerRouter extends FlutterErrorDetails {
     this.router,
     this.route,
     this.event,
-    FlutterInformationCollector informationCollector,
+    InformationCollector informationCollector,
     bool silent: false
   }) : super(
     exception: exception,

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

@@ -303,8 +303,17 @@ class BoxConstraints extends Constraints {
   }
 
   @override
-  bool debugAssertIsValid({ bool isAppliedConstraint: false }) {
+  bool debugAssertIsValid({
+    bool isAppliedConstraint: false,
+    InformationCollector informationCollector
+  }) {
     assert(() {
+      void throwError(String message) {
+        StringBuffer information = new StringBuffer();
+        if (informationCollector != null)
+          informationCollector(information);
+        throw new FlutterError('$message\n${information}The offending constraints were:\n  $this');
+      }
       if (minWidth.isNaN || maxWidth.isNaN || minHeight.isNaN || maxHeight.isNaN) {
         List<String> affectedFieldsList = <String>[];
         if (minWidth.isNaN)
@@ -326,27 +335,27 @@ class BoxConstraints extends Constraints {
         } else {
           whichFields = affectedFieldsList.single;
         }
-        throw new FlutterError('BoxConstraints has ${affectedFieldsList.length == 1 ? 'a NaN value' : 'NaN values' } in $whichFields.\n$this');
+        throwError('BoxConstraints has ${affectedFieldsList.length == 1 ? 'a NaN value' : 'NaN values' } in $whichFields.');
       }
       if (minWidth < 0.0 && minHeight < 0.0)
-        throw new FlutterError('BoxConstraints has both a negative minimum width and a negative minimum height.\n$this');
+        throwError('BoxConstraints has both a negative minimum width and a negative minimum height.');
       if (minWidth < 0.0)
-        throw new FlutterError('BoxConstraints has a negative minimum width.\n$this');
+        throwError('BoxConstraints has a negative minimum width.');
       if (minHeight < 0.0)
-        throw new FlutterError('BoxConstraints has a negative minimum height.\n$this');
+        throwError('BoxConstraints has a negative minimum height.');
       if (maxWidth < minWidth && maxHeight < minHeight)
-        throw new FlutterError('BoxConstraints has both width and height constraints non-normalized.\n$this');
+        throwError('BoxConstraints has both width and height constraints non-normalized.');
       if (maxWidth < minWidth)
-        throw new FlutterError('BoxConstraints has non-normalized width constraints.\n$this');
+        throwError('BoxConstraints has non-normalized width constraints.');
       if (maxHeight < minHeight)
-        throw new FlutterError('BoxConstraints has non-normalized height constraints.\n$this');
+        throwError('BoxConstraints has non-normalized height constraints.');
       if (isAppliedConstraint) {
         if (minWidth.isInfinite && minHeight.isInfinite)
-          throw new FlutterError('BoxConstraints requires infinite width and infinite height.\n$this');
+          throwError('BoxConstraints forces an infinite width and infinite height.');
         if (minWidth.isInfinite)
-          throw new FlutterError('BoxConstraints requires infinite width.\n$this');
+          throwError('BoxConstraints forces an infinite width.');
         if (minHeight.isInfinite)
-          throw new FlutterError('BoxConstraints requires infinite height.\n$this');
+          throwError('BoxConstraints forces an infinite height.');
       }
       assert(isNormalized);
       return true;

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

@@ -20,7 +20,7 @@ import 'binding.dart';
 
 export 'package:flutter/gestures.dart' show HitTestEntry, HitTestResult;
 export 'package:flutter/painting.dart';
-export 'package:flutter/services.dart' show FlutterError;
+export 'package:flutter/services.dart' show FlutterError, InformationCollector;
 
 /// Base class for data associated with a [RenderObject] by its parent.
 ///
@@ -389,7 +389,7 @@ abstract class Constraints {
   /// For example, the [BoxConstraints] subclass verifies that the
   /// constraints are not [NaN].
   ///
-  /// If the [isAppliedConstraint] argument is true, then even
+  /// If the `isAppliedConstraint` argument is true, then even
   /// stricter rules are enforced. This argument is set to true when
   /// checking constraints that are about to be applied to a
   /// [RenderObject] during layout, as opposed to constraints that may
@@ -399,8 +399,16 @@ abstract class Constraints {
   /// argument, but the asserts for verifying the argument passed to
   /// the [layout] method do.
   ///
+  /// The `informationCollector` argument takes an optional callback
+  /// which is called when an exception is to be thrown. The collected
+  /// information is then included in the message after the error
+  /// line.
+  ///
   /// Returns the same as [isNormalized] if asserts are disabled.
-  bool debugAssertIsValid({ bool isAppliedConstraint: false });
+  bool debugAssertIsValid({
+    bool isAppliedConstraint: false,
+    InformationCollector informationCollector
+  });
 }
 
 typedef void RenderObjectVisitor(RenderObject child);
@@ -900,13 +908,13 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
       context: 'during $method()',
       renderObject: this,
       informationCollector: (StringBuffer information) {
-        information.writeln('The following RenderObject was being processed when the exception was fired:\n${this}');
+        information.writeln('The following RenderObject was being processed when the exception was fired:\n  $this');
         if (debugCreator != null)
-          information.writeln('This RenderObject had the following creator:\n  $debugCreator');
+          information.writeln('This RenderObject had the following creator information:\n  $debugCreator');
         List<String> descendants = <String>[];
         const int maxDepth = 5;
         int depth = 0;
-        const int maxLines = 30;
+        const int maxLines = 25;
         int lines = 0;
         void visitor(RenderObject child) {
           if (lines < maxLines) {
@@ -1147,12 +1155,39 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
   /// override performResize and/or performLayout.
   ///
   /// The parent's performLayout method should call the layout of all its
-  /// children unconditionally. It is the layout functions's responsibility (as
+  /// children unconditionally. It is the layout function's responsibility (as
   /// implemented here) to return early if the child does not need to do any
   /// work to update its layout information.
   void layout(Constraints constraints, { bool parentUsesSize: false }) {
     assert(constraints != null);
-    assert(constraints.debugAssertIsValid(isAppliedConstraint: true));
+    assert(constraints.debugAssertIsValid(
+      isAppliedConstraint: true,
+      informationCollector: (StringBuffer information) {
+        List<String> stack = StackTrace.current.toString().split('\n');
+        int targetFrame;
+        Pattern layoutFramePattern = new RegExp(r'^#[0-9]+ +RenderObject.layout \(');
+        for (int i = 0; i < stack.length; i += 1) {
+          if (layoutFramePattern.matchAsPrefix(stack[i]) != null) {
+            targetFrame = i + 1;
+            break;
+          }
+        }
+        if (targetFrame != null && targetFrame < stack.length) {
+          information.writeln(
+            'These invalid constraints were provided to $runtimeType\'s method() ' 
+            'function by the following function, which probably computed the '
+            'invalid constraints in question:'
+          );
+          Pattern targetFramePattern = new RegExp(r'^#[0-9]+ +(.+)$');
+          Match targetFrameMatch = targetFramePattern.matchAsPrefix(stack[targetFrame]);
+          if (targetFrameMatch != null && targetFrameMatch.groupCount > 0) {
+            information.writeln('  ${targetFrameMatch.group(1)}');
+          } else {
+            information.writeln(stack[targetFrame]);
+          }
+        }
+      }
+    ));
     assert(!_debugDoingThisResize);
     assert(!_debugDoingThisLayout);
     final RenderObject parent = this.parent;
@@ -2189,7 +2224,7 @@ class FlutterErrorDetailsForRendering extends FlutterErrorDetails {
     String library,
     String context,
     this.renderObject,
-    FlutterInformationCollector informationCollector,
+    InformationCollector informationCollector,
     bool silent: false
   }) : super(
     exception: exception,

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

@@ -7,11 +7,9 @@ import 'print.dart';
 /// Signature for [FlutterError.onException] handler.
 typedef void FlutterExceptionHandler(FlutterErrorDetails details);
 
-/// Signature for [FlutterErrorDetails.informationCollector] callback.
-///
-/// The text written to the information argument may contain newlines but should
-/// not end with a newline.
-typedef void FlutterInformationCollector(StringBuffer information);
+/// Signature for [FlutterErrorDetails.informationCollector] callback
+/// and other callbacks that collect information into a string buffer.
+typedef void InformationCollector(StringBuffer information);
 
 /// Class for information provided to [FlutterExceptionHandler] callbacks.
 ///
@@ -56,7 +54,10 @@ class FlutterErrorDetails {
   ///
   /// Information collector callbacks can be expensive, so the generated information
   /// should be cached, rather than the callback being invoked multiple times.
-  final FlutterInformationCollector informationCollector;
+  ///
+  /// The text written to the information argument may contain newlines but should
+  /// not end with a newline.
+  final InformationCollector informationCollector;
 
   /// Whether this error should be ignored by the default error reporting
   /// behavior in release mode.
@@ -124,7 +125,7 @@ class FlutterError extends AssertionError {
 
   static int _errorCount = 0;
 
-  static const int _kWrapWidth = 120;
+  static const int _kWrapWidth = 100;
 
   /// Prints the given exception details to the console.
   ///

packages/flutter/test/rendering/constraints_test.dart

@@ -43,7 +43,8 @@ void main() {
     }
     expect(result, equals(
       'BoxConstraints has NaN values in minWidth, maxWidth, and maxHeight.\n'
-      'BoxConstraints(NaN<=w<=NaN, 2.0<=h<=NaN; NOT NORMALIZED)'
+      'The offending constraints were:\n'
+      '  BoxConstraints(NaN<=w<=NaN, 2.0<=h<=NaN; NOT NORMALIZED)'
     ));
 
     result = 'no exception';
@@ -55,7 +56,8 @@ void main() {
     }
     expect(result, equals(
       'BoxConstraints has a NaN value in minHeight.\n'
-      'BoxConstraints(0.0<=w<=Infinity, NaN<=h<=Infinity; NOT NORMALIZED)'
+      'The offending constraints were:\n'
+      '  BoxConstraints(0.0<=w<=Infinity, NaN<=h<=Infinity; NOT NORMALIZED)'
     ));
 
     result = 'no exception';
@@ -67,7 +69,8 @@ void main() {
     }
     expect(result, equals(
       'BoxConstraints has NaN values in maxWidth and minHeight.\n'
-      'BoxConstraints(0.0<=w<=NaN, NaN<=h<=Infinity; NOT NORMALIZED)'
+      'The offending constraints were:\n'
+      '  BoxConstraints(0.0<=w<=NaN, NaN<=h<=Infinity; NOT NORMALIZED)'
     ));
   });
 }