Improve intersection type parsing

src/Psalm/Checker/CommentChecker.php

@@ -157,10 +157,8 @@ class CommentChecker
                 && !strpos($line_parts[0], '::')
                 && $line_parts[0][0] !== '{'
             ) {
-                if ($line_parts[0][0] === '$' && $line_parts[0] !== '$this') {
+                if ($line_parts[0][0] === '$' && !preg_match('/^\$this(\||$)/', $line_parts[0])) {
-                    if ($line_parts[0][0] === '$' && $line_parts[0] !== '$this') {
+                    throw new IncorrectDocblockException('Misplaced variable');
-                        throw new IncorrectDocblockException('Misplaced variable');
-                    }
                 }
 
                 $info->return_type = $line_parts[0];
@@ -202,7 +200,7 @@ class CommentChecker
                             $line_parts[1] = substr($line_parts[1], 1);
                         }
 
-                        if ($line_parts[0][0] === '$' && $line_parts[0] !== '$this') {
+                        if ($line_parts[0][0] === '$' && !preg_match('/^\$this(\||$)/', $line_parts[0])) {
                             throw new IncorrectDocblockException('Misplaced variable');
                         }
 
@@ -351,7 +349,7 @@ class CommentChecker
                         $line_parts[1] = substr($line_parts[1], 1);
                     }
 
-                    if ($line_parts[0][0] === '$' && $line_parts[0] !== '$this') {
+                    if ($line_parts[0][0] === '$' && !preg_match('/^\$this(\||$)/', $line_parts[0])) {
                         throw new IncorrectDocblockException('Misplaced variable');
                     }
 

src/Psalm/Type.php

@@ -211,7 +211,7 @@ abstract class Type
 
             $first_type->extra_types = $intersection_types;
 
-            return new Type\Union([$first_type]);
+            return $first_type;
         }
 
         if ($parse_tree instanceof ParseTree\ObjectLikeTree) {
@@ -358,10 +358,6 @@ abstract class Type
                 !isset($template_types[$return_type_token])
             ) {
                 if ($return_type_token[0] === '$') {
-                    if ($return_type === '$this') {
-                        $return_type_token = 'static';
-                    }
-
                     continue;
                 }
 

src/Psalm/Type/Atomic.php

@@ -108,6 +108,9 @@ abstract class Atomic
             case 'class-string':
                 return new TClassString();
 
+            case '$this':
+                return new TNamedObject('static');
+
             default:
                 if (strpos($value, '-')) {
                     throw new \Psalm\Exception\TypeParseTreeException('no hyphens allowed');

src/Psalm/Type/Atomic/GenericTrait.php

@@ -18,7 +18,13 @@ trait GenericTrait
             $s .= $type_param . ', ';
         }
 
-        return $this->value . '<' . substr($s, 0, -2) . '>';
+        $extra_types = '';
+
+        if ($this instanceof TNamedObject && $this->extra_types) {
+            $extra_types = '&' . implode('&', $this->extra_types);
+        }
+
+        return $this->value . '<' . substr($s, 0, -2) . '>' . $extra_types;
     }
 
     /**
@@ -55,6 +61,23 @@ trait GenericTrait
             return $value_type_string . '[]';
         }
 
+        $extra_types = '';
+
+        if ($this instanceof TNamedObject && $this->extra_types) {
+            $extra_types = '&' . implode(
+                '&',
+                array_map(
+                    /**
+                     * @return string
+                     */
+                    function (Atomic $extra_type) use ($namespace, $aliased_classes, $this_class) {
+                        return $extra_type->toNamespacedString($namespace, $aliased_classes, $this_class, false);
+                    },
+                    $this->extra_types
+                )
+            );
+        }
+
         return $base_value .
                 '<' .
                 implode(
@@ -69,7 +92,7 @@ trait GenericTrait
                         $this->type_params
                     )
                 ) .
-                '>';
+                '>' . $extra_types;
     }
 
     public function __clone()

src/Psalm/Type/ParseTree.php

@@ -141,6 +141,11 @@ class ParseTree
                         continue;
                     }
 
+                    if ($current_parent && $current_parent instanceof ParseTree\IntersectionTree) {
+                        $current_leaf = $current_parent;
+                        $current_parent = $current_leaf->parent;
+                    }
+
                     $new_parent_leaf = new ParseTree\UnionTree($current_parent);
                     $new_parent_leaf->children = [$current_leaf];
                     $current_leaf->parent = $new_parent_leaf;
@@ -202,6 +207,10 @@ class ParseTree
                             throw new TypeParseTreeException('Cannot process bracket yet');
 
                         default:
+                            if ($type_token === '$this') {
+                                $type_token = 'static';
+                            }
+
                             $new_leaf = new ParseTree\Value(
                                 $type_token,
                                 $new_parent

tests/InterfaceTest.php

@@ -338,6 +338,21 @@ class InterfaceTest extends TestCase
                       }
                     }',
             ],
+            'implementThisReturn' => [
+                '<?php
+                    class A {}
+                    interface I {
+                      /** @return A */
+                      public function foo();
+                    }
+
+                    class B extends A implements I {
+                      /** @return $this */
+                      public function foo() {
+                        return $this;
+                      }
+                    }',
+            ],
             'inheritMultipleInterfacesWithDocblocks' => [
                 '<?php
                     interface I1 {

tests/TypeParseTest.php

@@ -13,6 +13,22 @@ class TypeParseTest extends TestCase
         //parent::setUp();
     }
 
+    /**
+     * @return void
+     */
+    public function testThisToStatic()
+    {
+        $this->assertSame('static', (string) Type::parseString('$this'));
+    }
+
+    /**
+     * @return void
+     */
+    public function testThisToStaticUnion()
+    {
+        $this->assertSame('static|A', (string) Type::parseString('$this|A'));
+    }
+
     /**
      * @return void
      */
@@ -87,6 +103,41 @@ class TypeParseTest extends TestCase
         $this->assertSame('I1&I2', (string) Type::parseString('I1&I2'));
     }
 
+    /**
+     * @return void
+     */
+    public function testIntersectionOrNull()
+    {
+        $this->assertSame('I1&I2|null', (string) Type::parseString('I1&I2|null'));
+    }
+
+    /**
+     * @return void
+     */
+    public function testNullOrIntersection()
+    {
+        $this->assertSame('null|I1&I2', (string) Type::parseString('null|I1&I2'));
+    }
+
+    /**
+     * @return void
+     */
+    public function testInteratorAndTraversable()
+    {
+        $this->assertSame('Iterator<int>&Traversable', (string) Type::parseString('Iterator<int>&Traversable'));
+    }
+
+    /**
+     * @return void
+     */
+    public function testTraversableAndIteratorOrNull()
+    {
+        $this->assertSame(
+            'Traversable&Iterator<int>|null',
+            (string) Type::parseString('Traversable&Iterator<int>|null')
+        );
+    }
+
     /**
      * @return void
      */

tests/TypeReconciliationTest.php

@@ -570,7 +570,10 @@ class TypeReconciliationTest extends TestCase
                     function takesIandA($a): void {}
 
                     class A {
-                        public function foo(): void {
+                        /**
+                         * @return A&I|null
+                         */
+                        public function foo() {
                             if ($this instanceof I) {
                                 $this->bar();
                                 $this->bat();