Migration: make an edge origin for assignments of dynamic.

Change-Id: I75d037aa7ee890488a92e113f58094b5733a9b8f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/125004
Reviewed-by: Mike Fairhurst <mfairhurst@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>

Author: stereotype441

pkg/nnbd_migration/lib/instrumentation.dart

@@ -128,6 +128,7 @@ enum EdgeOriginKind {
   alwaysNullableType,
   compoundAssignment,
   defaultValue,
+  dynamicAssignment,
   expressionChecks,
   fieldFormalParameter,
   forEachVariable,

pkg/nnbd_migration/lib/src/edge_builder.dart

@@ -1626,7 +1626,9 @@ class EdgeBuilder extends GeneralizingAstVisitor<DecoratedType>
             '(${expression.toSource()}) offset=${expression.offset}');
       }
       EdgeOrigin edgeOrigin;
-      if (!sourceType.type.isDynamic) {
+      if (sourceType.type.isDynamic) {
+        edgeOrigin = DynamicAssignmentOrigin(source, expression);
+      } else {
         if (fromDefaultValue) {
           edgeOrigin = DefaultValueOrigin(source, expression);
         } else {

pkg/nnbd_migration/lib/src/edge_origin.dart

@@ -70,6 +70,15 @@ class DefaultValueOrigin extends EdgeOrigin {
   EdgeOriginKind get kind => EdgeOriginKind.defaultValue;
 }
 
+/// An edge origin used for edges that originated because of an assignment
+/// involving a value with a dynamic type.
+class DynamicAssignmentOrigin extends EdgeOrigin {
+  DynamicAssignmentOrigin(Source source, AstNode node) : super(source, node);
+
+  @override
+  EdgeOriginKind get kind => EdgeOriginKind.dynamicAssignment;
+}
+
 /// Common interface for classes providing information about how an edge came
 /// to be; that is, what was found in the source code that led the migration
 /// tool to create the edge.

pkg/nnbd_migration/test/instrumentation_test.dart

@@ -407,6 +407,21 @@ int f(int x) => x;
     expect(origin.node, findNode.simple('x;'));
   }
 
+  test_graphEdge_origin_dynamic_assignment() async {
+    await analyze('''
+int f(dynamic x) => x;
+''');
+    var xNode = explicitTypeNullability[findNode.typeAnnotation('dynamic x')];
+    var returnNode = explicitTypeNullability[findNode.typeAnnotation('int f')];
+    var matchingEdges = edges
+        .where((e) => e.sourceNode == xNode && e.destinationNode == returnNode)
+        .toList();
+    var origin = edgeOrigin[matchingEdges.single];
+    expect(origin.kind, EdgeOriginKind.dynamicAssignment);
+    expect(origin.source, source);
+    expect(origin.node, findNode.simple('x;'));
+  }
+
   test_graphEdge_soft() async {
     await analyze('''
 int f(int x, bool b) {