TypeParser: add support for $this type

doc/grammars/type.ebnf

@@ -13,6 +13,7 @@ Nullable
 
 Atomic
   ::= Identifier (Generic | Array)?
+    | ThisType
     | '(' Type ')' Array?
 
 Generic
@@ -21,8 +22,11 @@ Generic
 Array
   ::= ('[' ']')+
 
+ThisType
+  ::= '$this'
+
 Identifier
-  ::= ('\'? Word)+
+  ::= ('\\'? Word)+
 
 Word
   ::= [a-zA-Z_#x7F-#x10FFFF][0-9a-zA-Z_#x7F-#x10FFFF]*

doc/grammars/type.peg

@@ -13,6 +13,7 @@ Nullable
 
 Atomic
   = Identifier (Generic / Array)?
+  / ThisType
   / '(' Type ')' Array?
 
 Generic
@@ -21,8 +22,11 @@ Generic
 Array
   = ('[' ']')+
 
+ThisType
+  = '$this'
+
 Identifier
-  = ('\'? Word)+
+  = ('\\'? Word)+
 
 Word
-  = [a-zA-Z_\127-\255\\][a-zA-Z0-9_\127-\255\\]*
+  = [a-zA-Z_\\127-\\255][a-zA-Z0-9_\\127-\\255]*

src/Ast/Type/ThisTypeNode.php

@@ -0,0 +1,12 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\PhpDocParser\Ast\Type;
+
+
+class ThisTypeNode implements TypeNode
+{
+	public function __toString(): string
+	{
+		return '$this';
+	}
+}

src/Parser/TypeParser.php

@@ -38,6 +38,9 @@ class TypeParser
 				$type = $this->parseArray($tokens, $type);
 			}
 
+		} elseif ($tokens->tryConsumeTokenType(Lexer::TOKEN_THIS_VARIABLE)) {
+			return new Ast\Type\ThisTypeNode();
+
 		} else {
 			$type = new Ast\Type\IdentifierTypeNode($tokens->currentTokenValue());
 			$tokens->consumeTokenType(Lexer::TOKEN_IDENTIFIER);