feat: allow taking pointerof(self) in structs

spec/compiler/parser/parser_spec.cr

@@ -2192,7 +2192,6 @@ module Crystal
     assert_syntax_error "case when .foo? then 1; end"
     assert_syntax_error "macro foo;{%end};end"
     assert_syntax_error "foo {1, 2}", %(unexpected token: ",")
-    assert_syntax_error "pointerof(self)", "can't take address of self"
     assert_syntax_error "def foo 1; end"
 
     assert_syntax_error %<{"x": [] of Int32,\n}\n1.foo(>, "unterminated call", 3, 6

src/compiler/crystal/semantic/main_visitor.cr

@@ -2599,6 +2599,14 @@ module Crystal
     def pointerof_var(node)
       case exp = node.exp
       when Var
+        if exp.name == "self"
+          exp.accept self
+
+          unless exp.type.struct?
+            node.raise "can only take address of self in struct"
+          end
+        end
+
         meta_var = @meta_vars[exp.name]
         meta_var.assigned_to = true
         meta_var

src/compiler/crystal/syntax/parser.cr

@@ -5919,10 +5919,6 @@ module Crystal
       check :OP_LPAREN
       next_token_skip_space_or_newline
 
-      if @token.keyword?(:self)
-        raise "can't take address of self", @token.line_number, @token.column_number
-      end
-
       exp = parse_op_assign
       skip_space_or_newline