hhvm 4.97 issue: x\node should permit ?XHPChild children about xhp-lib

[fredemmott]

use type Facebook\XHP\HTML\div;

function test(): void {
  $x = <div>{null}</div>;
}

This should be equivalent to <div></div>. Instead:

Typing[4110] Some elements in this collection are incompatible [1]
-> Expected XHPChild [2]
-> But got null [3]

src/test.hack:4:8
       2 |
       3 | function test(): void {
[1,3]  4 |   $x = <div>{null}</div>;
       5 | }

vendor/facebook/xhp-lib/src/core/Node.hack:52:17
      50 |   final public function __construct(
      51 |     KeyedTraversable<string, mixed> $attributes,
[2]   52 |     Traversable<\XHPChild> $children,
      53 |     dynamic ...$debug_info
      54 |   ) {

[jjergus]

Yep I included this as a breaking change in the release notes:

The typechecker now checks XHP constructor calls (bad calls would previously result in a runtime error, but wouldn’t be caught by the typechecker). This may reveal new errors, but it should be rare, since XHP class declarations rarely override the built-in default constructor, and are usually instantiated using the standard XHP syntax instead of explicit constructor calls.

Of course, whenever someone declares a bug to be rare, it will immediately happen.

Fixed in both v4 and v3, also tagged a release of each since it was blocking updating the docs site and other projects.

7d2d31e
e21656f

(also includes a test case)