Add a hint on static uses of fuzzy arrows.

pkg/analyzer/lib/src/generated/type_system.dart

Index: pkg/analyzer/lib/src/generated/type_system.dart
diff --git a/pkg/analyzer/lib/src/generated/type_system.dart b/pkg/analyzer/lib/src/generated/type_system.dart
index 1ed098dd935d46568487bf3b8e8d3eba1d188225..931764d34e980e325562a41500e5ecc214a00a01 100644
--- a/pkg/analyzer/lib/src/generated/type_system.dart
+++ b/pkg/analyzer/lib/src/generated/type_system.dart
@@ -47,6 +47,8 @@ typedef bool _GuardedSubtypeChecker<T>(T t1, T t2, Set<TypeImpl> visitedTypes);
 class StrongTypeSystemImpl extends TypeSystem {
   static bool _comparingTypeParameterBounds = false;
 
+  bool allowDynamicAsBottom = true;
+
   /**
    * True if declaration casts should be allowed, otherwise false.
    *
@@ -135,6 +137,8 @@ class StrongTypeSystemImpl extends TypeSystem {
   /// Computes the greatest lower bound of [type1] and [type2].
   DartType getGreatestLowerBound(DartType type1, DartType type2,
       {dynamicIsBottom: false}) {
+    dynamicIsBottom = dynamicIsBottom && allowDynamicAsBottom;
+
     // The greatest lower bound relation is reflexive.
     if (identical(type1, type2)) {
       return type1;
@@ -211,6 +215,8 @@ class StrongTypeSystemImpl extends TypeSystem {
   @override
   DartType getLeastUpperBound(DartType type1, DartType type2,
       {bool dynamicIsBottom: false}) {
+    dynamicIsBottom = dynamicIsBottom && allowDynamicAsBottom;
+
     if (isNullableType(type1) && isNonNullableType(type2)) {
       assert(type2 is InterfaceType);
       type2 = getLeastNullableSupertype(type2 as InterfaceType);
@@ -476,7 +482,8 @@ class StrongTypeSystemImpl extends TypeSystem {
 
     if (t is FunctionType) {
       if (!_isTop(t.returnType) ||
-          anyParameterType(t, (pt) => !_isBottom(pt, dynamicIsBottom: true))) {
+          anyParameterType(t,
+              (pt) => !_isBottom(pt, dynamicIsBottom: allowDynamicAsBottom))) {
         return false;
       } else {
         return true;
@@ -645,7 +652,8 @@ class StrongTypeSystemImpl extends TypeSystem {
       DartType paramType;
       if (fType != null && gType != null) {
         // If both functions have this parameter, include both of their types.
-        paramType = getLeastUpperBound(fType, gType, dynamicIsBottom: true);
+        paramType = getLeastUpperBound(fType, gType,
+            dynamicIsBottom: allowDynamicAsBottom);
       } else {
         paramType = fType ?? gType;
       }
@@ -727,7 +735,7 @@ class StrongTypeSystemImpl extends TypeSystem {
 
   @override
   DartType _functionParameterBound(DartType f, DartType g) =>
-      getGreatestLowerBound(f, g, dynamicIsBottom: true);
+      getGreatestLowerBound(f, g, dynamicIsBottom: allowDynamicAsBottom);
 
   /// Given a type return its name prepended with the URI to its containing
   /// library and separated by a comma.
@@ -811,7 +819,7 @@ class StrongTypeSystemImpl extends TypeSystem {
     return FunctionTypeImpl.relate(f1, f2, isSubtypeOf, instantiateToBounds,
         parameterRelation: (p1, p2) => _isSubtypeOf(
             p2.type, p1.type, visitedTypes,
-            dynamicIsBottom: true));
+            dynamicIsBottom: allowDynamicAsBottom));
   }
 
   bool _isInterfaceSubtypeOf(
@@ -870,6 +878,8 @@ class StrongTypeSystemImpl extends TypeSystem {
 
   bool _isSubtypeOf(DartType t1, DartType t2, Set<TypeImpl> visitedTypes,
       {bool dynamicIsBottom: false}) {
+    dynamicIsBottom = dynamicIsBottom && allowDynamicAsBottom;
+
     if (identical(t1, t2)) {
       return true;
     }
@@ -980,6 +990,8 @@ class StrongTypeSystemImpl extends TypeSystem {
 
   DartType _substituteForUnknownType(DartType type,
       {bool lowerBound: false, dynamicIsBottom: false}) {
+    dynamicIsBottom = dynamicIsBottom && allowDynamicAsBottom;
+
     if (identical(type, UnknownInferredType.instance)) {
       if (lowerBound && !dynamicIsBottom) {
         // TODO(jmesserly): this should be the bottom type, once i can be
@@ -1003,7 +1015,7 @@ class StrongTypeSystemImpl extends TypeSystem {
         // Parameters are contravariant, so flip the constraint direction.
         // Also pass dynamicIsBottom, because this is a fuzzy arrow.
         var newType = _substituteForUnknownType(p.type,
-            lowerBound: !lowerBound, dynamicIsBottom: true);
+            lowerBound: !lowerBound, dynamicIsBottom: allowDynamicAsBottom);
         return new ParameterElementImpl.synthetic(
             p.name, newType, p.parameterKind);
       });