Add UnlinkedConst.isValid and set it during summarizing.

pkg/analyzer/lib/src/summary/format.dart

Index: pkg/analyzer/lib/src/summary/format.dart
diff --git a/pkg/analyzer/lib/src/summary/format.dart b/pkg/analyzer/lib/src/summary/format.dart
index 4dc69dc7e194947bed0fb696e4adc0120baf2d9e..020e4faa926cea3a4b2bc4c5514e9e9dc06d7ef0 100644
--- a/pkg/analyzer/lib/src/summary/format.dart
+++ b/pkg/analyzer/lib/src/summary/format.dart
@@ -1623,6 +1623,7 @@ abstract class _UnlinkedCombinatorMixin implements idl.UnlinkedCombinator {
 class UnlinkedConstBuilder extends Object with _UnlinkedConstMixin implements idl.UnlinkedConst {
   bool _finished = false;
 
+  bool _isValid;
   List<idl.UnlinkedConstOperation> _operations;
   List<int> _ints;
   List<double> _doubles;
@@ -1630,6 +1631,18 @@ class UnlinkedConstBuilder extends Object with _UnlinkedConstMixin implements id
   List<EntityRefBuilder> _references;
 
   @override
+  bool get isValid => _isValid ??= false;
+
+  /**
+   * Indicates whether the expression is a valid potentially constant
+   * expression.
+   */
+  void set isValid(bool _value) {
+    assert(!_finished);
+    _isValid = _value;
+  }
+
+  @override
   List<idl.UnlinkedConstOperation> get operations => _operations ??= <idl.UnlinkedConstOperation>[];
 
   /**
@@ -1692,8 +1705,9 @@ class UnlinkedConstBuilder extends Object with _UnlinkedConstMixin implements id
     _references = _value;
   }
 
-  UnlinkedConstBuilder({List<idl.UnlinkedConstOperation> operations, List<int> ints, List<double> doubles, List<String> strings, List<EntityRefBuilder> references})
-    : _operations = operations,
+  UnlinkedConstBuilder({bool isValid, List<idl.UnlinkedConstOperation> operations, List<int> ints, List<double> doubles, List<String> strings, List<EntityRefBuilder> references})
+    : _isValid = isValid,
+      _operations = operations,
       _ints = ints,
       _doubles = doubles,
       _strings = strings,
@@ -1723,20 +1737,23 @@ class UnlinkedConstBuilder extends Object with _UnlinkedConstMixin implements id
       offset_references = fbBuilder.writeList(_references.map((b) => b.finish(fbBuilder)).toList());
     }
     fbBuilder.startTable();
+    if (_isValid == true) {
+      fbBuilder.addBool(0, true);
+    }
     if (offset_operations != null) {
-      fbBuilder.addOffset(0, offset_operations);
+      fbBuilder.addOffset(1, offset_operations);
     }
     if (offset_ints != null) {
-      fbBuilder.addOffset(1, offset_ints);
+      fbBuilder.addOffset(2, offset_ints);
     }
     if (offset_doubles != null) {
-      fbBuilder.addOffset(2, offset_doubles);
+      fbBuilder.addOffset(3, offset_doubles);
     }
     if (offset_strings != null) {
-      fbBuilder.addOffset(3, offset_strings);
+      fbBuilder.addOffset(4, offset_strings);
     }
     if (offset_references != null) {
-      fbBuilder.addOffset(4, offset_references);
+      fbBuilder.addOffset(5, offset_references);
     }
     return fbBuilder.endTable();
   }
@@ -1754,6 +1771,7 @@ class _UnlinkedConstImpl extends Object with _UnlinkedConstMixin implements idl.
 
   _UnlinkedConstImpl(this._bp);
 
+  bool _isValid;
   List<idl.UnlinkedConstOperation> _operations;
   List<int> _ints;
   List<double> _doubles;
@@ -1761,32 +1779,38 @@ class _UnlinkedConstImpl extends Object with _UnlinkedConstMixin implements idl.
   List<idl.EntityRef> _references;
 
   @override
+  bool get isValid {
+    _isValid ??= const fb.BoolReader().vTableGet(_bp, 0, false);
+    return _isValid;
+  }
+
+  @override
   List<idl.UnlinkedConstOperation> get operations {
-    _operations ??= const fb.ListReader<idl.UnlinkedConstOperation>(const _UnlinkedConstOperationReader()).vTableGet(_bp, 0, const <idl.UnlinkedConstOperation>[]);
+    _operations ??= const fb.ListReader<idl.UnlinkedConstOperation>(const _UnlinkedConstOperationReader()).vTableGet(_bp, 1, const <idl.UnlinkedConstOperation>[]);
     return _operations;
   }
 
   @override
   List<int> get ints {
-    _ints ??= const fb.ListReader<int>(const fb.Uint32Reader()).vTableGet(_bp, 1, const <int>[]);
+    _ints ??= const fb.ListReader<int>(const fb.Uint32Reader()).vTableGet(_bp, 2, const <int>[]);
     return _ints;
   }
 
   @override
   List<double> get doubles {
-    _doubles ??= const fb.Float64ListReader().vTableGet(_bp, 2, const <double>[]);
+    _doubles ??= const fb.Float64ListReader().vTableGet(_bp, 3, const <double>[]);
     return _doubles;
   }
 
   @override
   List<String> get strings {
-    _strings ??= const fb.ListReader<String>(const fb.StringReader()).vTableGet(_bp, 3, const <String>[]);
+    _strings ??= const fb.ListReader<String>(const fb.StringReader()).vTableGet(_bp, 4, const <String>[]);
     return _strings;
   }
 
   @override
   List<idl.EntityRef> get references {
-    _references ??= const fb.ListReader<idl.EntityRef>(const _EntityRefReader()).vTableGet(_bp, 4, const <idl.EntityRef>[]);
+    _references ??= const fb.ListReader<idl.EntityRef>(const _EntityRefReader()).vTableGet(_bp, 5, const <idl.EntityRef>[]);
     return _references;
   }
 }
@@ -1794,6 +1818,7 @@ class _UnlinkedConstImpl extends Object with _UnlinkedConstMixin implements idl.
 abstract class _UnlinkedConstMixin implements idl.UnlinkedConst {
   @override
   Map<String, Object> toMap() => {
+    "isValid": isValid,
     "operations": operations,
     "ints": ints,
     "doubles": doubles,
@@ -3154,8 +3179,9 @@ class UnlinkedParamBuilder extends Object with _UnlinkedParamMixin implements id
   UnlinkedConstBuilder get defaultValue => _defaultValue;
 
   /**
-   * If the parameter has a default value the constant expression in the
-   * default value.
+   * If the parameter has a default value, the constant expression in the
+   * default value.  Note that the presence of this expression does not mean
+   * that it is a valid , check [UnlinkedConst.isValid].
    */
   void set defaultValue(UnlinkedConstBuilder _value) {
     assert(!_finished);
@@ -4587,7 +4613,8 @@ class UnlinkedVariableBuilder extends Object with _UnlinkedVariableMixin impleme
 
   /**
    * If [isConst] is true, and the variable has an initializer, the constant
-   * expression in the initializer.
+   * expression in the initializer.  Note that the presence of this expression
+   * does not mean that it is a valid, check [UnlinkedConst.isValid].
    */
   void set constExpr(UnlinkedConstBuilder _value) {
     assert(!_finished);