Refactor fuzzy arrow hints.

pkg/analyzer/lib/src/task/strong/checker.dart

Index: pkg/analyzer/lib/src/task/strong/checker.dart
diff --git a/pkg/analyzer/lib/src/task/strong/checker.dart b/pkg/analyzer/lib/src/task/strong/checker.dart
index e09f6af3f3b8fec50d6c82c46e312c3ac9826b7d..505f549b3ce82e74d4d8a0decd008852096e7daf 100644
--- a/pkg/analyzer/lib/src/task/strong/checker.dart
+++ b/pkg/analyzer/lib/src/task/strong/checker.dart
@@ -772,6 +772,8 @@ class CodeChecker extends RecursiveAstVisitor {
       {DartType from, bool opAssign: false, bool isDeclarationCast: false}) {
     from ??= _getDefiniteType(expr);
 
+    _hintOnFuzzyArrows(expr, to, from);
+
     if (_needsImplicitCast(expr, to,
             from: from, isDeclarationCast: isDeclarationCast) ==
         true) {
@@ -1075,6 +1077,19 @@ class CodeChecker extends RecursiveAstVisitor {
     return rules.anyParameterType(ft, (pt) => pt.isDynamic);
   }
 
+  void _hintOnFuzzyArrows(Expression expr, DartType to, DartType from) {
+    // If it is a subtype with fuzzy arrows on,
+    // check to see if it still is with them off.
+    if (rules.isSubtypeOf(from, to)) {
+      // Remove fuzzy arrows
+      var cFrom = rules.typeToConcreteType(from);
+      var cTo = rules.typeToConcreteType(to);
+      // If still true, no warning needed
+      if (rules.isSubtypeOf(cFrom, cTo)) return;
+      _recordMessage(expr, HintCode.USES_DYNAMIC_AS_BOTTOM, [from, to]);
+    }
+  }
+
   /// Returns true if we need an implicit cast of [expr] from [from] type to
   /// [to] type, returns false if no cast is needed, and returns null if the
   /// types are statically incompatible.
@@ -1224,7 +1239,9 @@ class CodeChecker extends RecursiveAstVisitor {
         errorCode.name.startsWith('STRONG_MODE_TOP_LEVEL_')) {
       severity = ErrorSeverity.ERROR;
     }
-    if (severity != ErrorSeverity.INFO || _options.strongModeHints) {
+    if (severity != ErrorSeverity.INFO ||
+        _options.strongModeHints ||
+        errorCode == HintCode.USES_DYNAMIC_AS_BOTTOM) {
       int begin = node is AnnotatedNode
           ? node.firstTokenAfterCommentAndMetadata.offset
           : node.offset;