Migration: add edge builder support for generic method invocations.

This should address ~25 exceptions whose stack trace includes the line:

EdgeBuilder.visitMethodDeclaration (package:nnbd_migration/src/edge_builder.dart:843:7)

Change-Id: I0076592f43f18c68f499fc9a80347a73033f8919
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/115802
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>

pkg/nnbd_migration/lib/src/edge_builder.dart

@@ -839,9 +839,6 @@ class EdgeBuilder extends GeneralizingAstVisitor<DecoratedType>
 
   @override
   DecoratedType visitMethodDeclaration(MethodDeclaration node) {
-    if (node.typeParameters != null) {
-      _unimplemented(node, 'Generic method');
-    }
     _handleExecutableDeclaration(node, node.declaredElement, node.metadata,
         node.returnType, node.parameters, null, node.body, null);
     return null;

pkg/nnbd_migration/test/edge_builder_test.dart

@@ -1749,6 +1749,29 @@ int/*2*/ g() {
             hard: false));
   }
 
+  test_genericMethodInvocation() async {
+    await analyze('''
+class Base {
+  T foo<T>(T x) => x;
+}
+class Derived extends Base {}
+int bar(Derived d, int i) => d.foo(i);
+''');
+    var implicitTypeArgumentMatcher = anyNode;
+    assertEdge(
+        decoratedTypeAnnotation('int i').node,
+        substitutionNode(
+            implicitTypeArgumentMatcher, decoratedTypeAnnotation('T x').node),
+        hard: true);
+    var implicitTypeArgumentNullability =
+        implicitTypeArgumentMatcher.matchingNode;
+    assertEdge(
+        substitutionNode(implicitTypeArgumentNullability,
+            decoratedTypeAnnotation('T foo').node),
+        decoratedTypeAnnotation('int bar').node,
+        hard: false);
+  }
+
   test_if_condition() async {
     await analyze('''
 void f(bool b) {

pkg/nnbd_migration/test/migration_visitor_test_base.dart

@@ -21,6 +21,19 @@ import 'package:test/test.dart';
 
 import 'abstract_single_unit.dart';
 
+/// A [NodeMatcher] that matches any node, and records what node it matched to.
+class AnyNodeMatcher implements NodeMatcher {
+  final List<NullabilityNode> _matchingNodes = [];
+
+  NullabilityNode get matchingNode => _matchingNodes.single;
+
+  @override
+  bool matches(NullabilityNode node) {
+    _matchingNodes.add(node);
+    return true;
+  }
+}
+
 /// Mixin allowing unit tests to create decorated types easily.
 mixin DecoratedTypeTester implements DecoratedTypeTesterBase {
   int _offset = 0;
@@ -114,7 +127,7 @@ class EdgeBuilderTestBase extends MigrationVisitorTestBase {
 /// Mixin allowing unit tests to check for the presence of graph edges.
 mixin EdgeTester {
   /// Returns a [NodeMatcher] that matches any node whatsoever.
-  NodeMatcher get anyNode => const _AnyNodeMatcher();
+  AnyNodeMatcher get anyNode => AnyNodeMatcher();
 
   NullabilityGraphForTesting get graph;
 
@@ -337,14 +350,6 @@ abstract class NodeMatcher {
   bool matches(NullabilityNode node);
 }
 
-/// A [NodeMatcher] that matches any node.
-class _AnyNodeMatcher implements NodeMatcher {
-  const _AnyNodeMatcher();
-
-  @override
-  bool matches(NullabilityNode node) => true;
-}
-
 /// A [NodeMatcher] that matches exactly one node.
 class _ExactNodeMatcher implements NodeMatcher {
   final NullabilityNode _expectation;