PHP8: Union types support

[Wulfheart]

#486

[czosel]

We're parsing function (Foo $foo): Bar {} as

{
      "kind": "function",
      "name": {
        "kind": "identifier",
        "name": false
      },
      "arguments": [
        {
          "kind": "parameter",
          "name": {
            "kind": "identifier",
            "name": "foo"
          },
          "value": null,
          "type": {
            "kind": "name",
            "resolution": "uqn",
            "name": "Foo"
          },
          "byref": false,
          "variadic": false,
          "nullable": false
        }
      ],
      "byref": false,
      "type": {
        "kind": "name",
        "resolution": "uqn",
        "name": "Bar"
      },
      "nullable": false,
      "body": {
        "kind": "block",
        "children": []
      }

PHP-Parser parses function (Foo|Bar $foo): Baz|Buzz {}; as

expr: Expr_Closure(
            attrGroups: array(
            )
            static: false
            byRef: false
            params: array(
                0: Param(
                    attrGroups: array(
                    )
                    flags: 0
                    type: UnionType(
                        types: array(
                            0: Name(
                                parts: array(
                                    0: Foo
                                )
                            )
                            1: Name(
                                parts: array(
                                    0: Bar
                                )
                            )
                        )
                    )
                    byRef: false
                    variadic: false
                    var: Expr_Variable(
                        name: foo
                    )
                    default: null
                )
            )
            uses: array(
            )
            returnType: UnionType(
                types: array(
                    0: Name(
                        parts: array(
                            0: Baz
                        )
                    )
                    1: Name(
                        parts: array(
                            0: Buzz
                        )
                    )
                )
            )
            stmts: array(
            )
        )

We could introduce a uniontype node, e.g.

      "type": {
        "kind": "uniontype",
        "types": [{
          "kind": "name",
          "resolution": "uqn",
          "name": "Foo"
        }, {
          "kind": "name",
          "resolution": "uqn",
          "name": "Foo"
        }]
      },

See also https://github.com/php/php-src/blob/493524454d66adde84e00d249d607ecd540de99f/Zend/zend_language_parser.y#L650

cc @ichiriac

[cseufert]

I have had a go at implementing this a changing type to an array, rather than a single value. Sorry I missed this before I started. I can update it to return a union type when there are multiple types.

[alexander-akait]

Fixed in php8 branch