Fix #970 - improve handling of yield from statements

src/Psalm/Visitor/DependencyFinderVisitor.php

@@ -448,7 +448,7 @@ class DependencyFinderVisitor extends PhpParser\NodeVisitorAbstract implements P
                     }
                 }
             }
-        } elseif ($node instanceof PhpParser\Node\Expr\Yield_) {
+        } elseif ($node instanceof PhpParser\Node\Expr\Yield_ || $node instanceof PhpParser\Node\Expr\YieldFrom) {
             $function_like_storage = end($this->functionlike_storages);
 
             if ($function_like_storage) {

tests/Php70Test.php

@@ -323,6 +323,13 @@ class Php70Test extends TestCase
                         takesString($s);
                     }',
             ],
+            'expectNonNullableTypeWithYield' => [
+                '<?php
+                    function example() : Generator {
+                        yield from [2];
+                        return null;
+                    }',
+            ],
         ];
     }
 
@@ -350,6 +357,21 @@ class Php70Test extends TestCase
                     };',
                 'error_message' => 'InvalidReturnStatement',
             ],
+            'expectNonNullableTypeWithNullReturn' => [
+                '<?php
+                    function example() : Generator {
+                        yield from [2];
+                        return null;
+                    }
+
+                    function example2() : Generator {
+                        if (rand(0, 1)) {
+                            return example();
+                        }
+                        return null;
+                    }',
+                'error_message' => 'NullableReturnStatement',
+            ],
         ];
     }
 }