Add OpenXR CTS test for API layer pre-create operations

[johnkearney]

OpenXR API Layers may need to query other layers or the runtime before the instance has been created - add an explicit test for this case.

This is an external mirror of https://gitlab.khronos.org/openxr/openxr/-/merge_requests/3415

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[johnkearney]

@fredemmott I've copied the CTS test that I've been working on in the working group gitlab here in case you happen to have views on how it should be implemented.

I see your existing loader spec change: KhronosGroup/OpenXR-SDK-Source#490 and OpenXR spec change: KhronosGroup/OpenXR-Docs#173 which seem to be connected to this; and the recent bug in Meta PC v68 release.

[fredemmott]

Thanks; I’ll take a look through when I can. Those PRs are really the easy half of the problem: I see them as only clarifying behavior that is already required by various parts of the spec.

I think the behavior that the loader spec requires for xrEnumerateApiLayerProperties is incorrect, and needs to be similar to instance extensions ; I just wanted to put up the less controversial PRs first

[fredemmott]

It would be useful to check xrEnumerateInstanceExtensionProperties both before and after creating an instance: if this layer is above other layers adding extensions (e.g. HTC, Ultraleap), the list may change.

Given the values can change at runtime according to the spec, there isn't a correct before-and-after set of values that applies generically, but it would be good to test it works.

It would be good to preemptively add a similar test for xrEnumerateApiLayerProperties - there have been several similar bugs in hardware vendor's API layers, but not - yet - in a runtime.

The spec issue for xrEnumerateApiLayerProperties is:

"xrEnumerateApiLayerProperties must: return only its own API layer properties."

Say you have game -> layer A -> layer B -> layer C -> runtime; by a strict reading:

1. layer A can see that layer B exists
2. layer B can see that layer C exists
3. layer A can not see that layer C exists, because B must 'only return its own API layer properties'

I believe that 3 is undesirable and surprising behavior; instead, layer A should be able to see both layer B and layer C. The spec should be changed (and I'm happy to create PRs) to be more similar to the xrEnumerateInstanceExtensionProperties - though, more specifically, layer B should be required to prepend its' own information:

• unlike with extensions, order matters for layers
• if it is prepended, while this would be a spec change adding more requirements, I do not believe there is a conformant way for a caller to depend on the old behavior: callers must allocate a buffer of the correct size, they must not assume it only has 0 or 1 entries.

[rpavlik]

A revised version of this PR has been merged internally.

[rpavlik]

That revised version is now released.