Infer Null for return type of functions with empty returns.

pkg/analyzer/test/src/task/strong/checker_test.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.test.src.task.strong.checker_test;
 
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import 'strong_test_helper.dart';
 
@@ skipping 2371 matching lines @@
 // function typed formal
 void ftf0(void x(/*error:IMPLICIT_DYNAMIC_PARAMETER*/y)) {}
 void ftf1(void x(int y)) {}
     ''');
     check(implicitDynamic: false);
   }
 
   void test_implicitDynamic_return() {
     addFile(r'''
 // function
-/*error:IMPLICIT_DYNAMIC_RETURN*/f0() {}
+/*error:IMPLICIT_DYNAMIC_RETURN*/f0() {return f0();}
 dynamic f1() { return 42; }
 
 // nested function
 void main() {
-  /*error:IMPLICIT_DYNAMIC_RETURN*/g0() {}
+  /*error:IMPLICIT_DYNAMIC_RETURN*/g0() {return g0();}
   dynamic g1() { return 42; }
 }
 
 // methods
 class B {
   int m1() => 42;
 }
 class C extends B {
   /*error:IMPLICIT_DYNAMIC_RETURN*/m0() => 123;
   m1() => 123;
@@ skipping 831 matching lines @@
     : g = f ?? _alwaysTrue;
   C.a() : g = _alwaysTrue;
 }
     ''');
   }
 
   void test_optionalParams() {
     // Regression test for https://github.com/dart-lang/sdk/issues/26155
     checkFile(r'''
 void takesF(void f(int x)) {
-  takesF(/*info:INFERRED_TYPE_CLOSURE,info:INFERRED_TYPE_CLOSURE*/([x]) { bool z = x.isEven; });
-  takesF(/*info:INFERRED_TYPE_CLOSURE*/(y) { bool z = y.isEven; });
+  takesF(/*info:INFERRED_TYPE_CLOSURE,
+           info:INFERRED_TYPE_CLOSURE*/([x]) { bool z = x.isEven; });
+  takesF(/*info:INFERRED_TYPE_CLOSURE,
+           info:INFERRED_TYPE_CLOSURE*/(y) { bool z = y.isEven; });
 }
     ''');
   }
 
   void test_overrideNarrowsType() {
     addFile(r'''
 class A {}
 class B extends A {}
 
 abstract class C {
@@ skipping 827 matching lines @@
     // Regression test for https://github.com/dart-lang/sdk/issues/25069
     checkFile('''
 typedef int Foo();
 void foo() {}
 void main () {
   Foo x = /*error:INVALID_ASSIGNMENT,info:USE_OF_VOID_RESULT*/foo();
 }
 ''');
   }
 }