Migration: handle an assignment from a type parameter's bound to its type.

stereotype441 · commit-bot@chromium.org · commit 83ab0a5ea962 · 2019-08-07T15:15:00.000Z
Change-Id: Iceda253691735fa3b8104f76f14b596aa4bd621a Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/112145 Reviewed-by: Dan Rubel <danrubel@google.com> Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
diff --git a/pkg/nnbd_migration/lib/src/edge_builder.dart b/pkg/nnbd_migration/lib/src/edge_builder.dart
@@ -1438,6 +1438,8 @@ $stackTrace''');
 mixin _AssignmentChecker {
   DecoratedClassHierarchy get _decoratedClassHierarchy;
 
+  NullabilityGraph get _graph;
+
   TypeSystem get _typeSystem;
 
   /// Creates the necessary constraint(s) for an assignment from [source] to
@@ -1470,6 +1472,14 @@ mixin _AssignmentChecker {
             hard: false);
         return;
       }
+    } else if (destinationType is TypeParameterType) {
+      // Effectively this is a downcast assignment from the source type to the
+      // type parameter's bound.
+      _checkAssignment(origin,
+          source: source,
+          destination:
+              _getTypeParameterTypeBound(destination).withNode(_graph.always),
+          hard: false);
     } else if (sourceType is InterfaceType &&
         destinationType is InterfaceType) {
       if (_typeSystem.isSubtypeOf(sourceType, destinationType)) {
diff --git a/pkg/nnbd_migration/test/edge_builder_test.dart b/pkg/nnbd_migration/test/edge_builder_test.dart
@@ -134,6 +134,19 @@ class AssignmentCheckerTest extends Object with EdgeTester {
     assertEdge(never, t.node, hard: false);
   }
 
+  void test_complex_to_typeParam() {
+    var bound = list(object());
+    var t = TypeParameterElementImpl.synthetic('T')..bound = bound.type;
+    checker.bounds[t] = bound;
+    var t1 = list(object());
+    var t2 = typeParameterType(t);
+    assign(t1, t2, hard: true);
+    assertEdge(t1.node, t2.node, hard: true);
+    assertNoEdge(t1.node, bound.node);
+    assertEdge(t1.typeArguments[0].node, bound.typeArguments[0].node,
+        hard: false);
+  }
+
   void test_dynamic_to_dynamic() {
     assign(dynamic_, dynamic_);
     // Note: no assertions to do; just need to make sure there wasn't a crash.
@@ -411,6 +424,22 @@ void f(int i) {
     assertEdge(decoratedTypeAnnotation('int i').node, never, hard: true);
   }
 
+  test_assign_bound_to_type_parameter() async {
+    await analyze('''
+class C<T extends List<int>> {
+  T f(List<int> x) => x;
+}
+''');
+    var boundType = decoratedTypeAnnotation('List<int>>');
+    var parameterType = decoratedTypeAnnotation('List<int> x');
+    var tType = decoratedTypeAnnotation('T f');
+    assertEdge(parameterType.node, tType.node, hard: true);
+    assertNoEdge(parameterType.node, boundType.node);
+    assertEdge(
+        parameterType.typeArguments[0].node, boundType.typeArguments[0].node,
+        hard: false);
+  }
+
   test_assign_null_to_generic_type() async {
     await analyze('''
 main() {
