Fix a bug where newer RenderMan shading nodes would be skipped when exporting Usd from Maya

[katpet]

Fix a bug where newer RenderMan shading nodes would be skipped when exporting Usd from Maya. There is a hardcoded map in maya-usd/lib/mayaUsd/fileio/shading/rfmShaderMap.h, and newer nodes that don't appear in that map were being skipped. I don't think the map is necessary for nodes that don't actually require a name mapping; it would be difficult to keep the list up to date. This change adds some code that falls back to assuming the rendermanForMaya writer is appropriate for nodes that would otherwise have been skipped.

[katpet]

This was my first time digging into this code, so there may be a better way to go about this. Or there may be some conditional necessary before going ahead and using the rendermanForMaya writer for unknown nodes. This change does fix the bug for my examples though. Let me know if you need advice on reproducing the problem.

[seando-adsk]

@katpet Thank you for submitting a pull-request, however before proceeding you will need to sign the Contributor License Agreement (CLA).

Sean

[seando-adsk]

@katpet Closing this PR as we never received a signed CLA from you. If you wish to continue please submit a signed CLA.

Sean

[katpet]

Hi, I believe a CLA has been submitted by my company. Can this pull request be reopened?

[seando-adsk]

@katpet Yes feel free to reopen. Can you verify if the CLA was sent (to email address). I haven't received any CLA yet.

Sean

[neilh-adsk]

New updated CLA received, reopened the PR

[seando-adsk]

@katpet Sorry for the delay. I missed that the CLA had been submitted and this PR was stuck in "do not merge" state. I've started the preflight.

[seando-adsk]

@katpet Unfortunately there are test errors on every platform and version of Maya:

======================================================================
ERROR: testEditAndBatchMergeRigMayaRefs (testCacheToUsd.CacheToUsdTestCase)
Test editing then merge a Maya Reference to a complex animated rig.
----------------------------------------------------------------------
Traceback (most recent call last):
  File ".../maya-usd/test/lib/mayaUsd/fileio/testCacheToUsd.py", line 555, in testEditAndBatchMergeRigMayaRefs
    self.assertTrue(mayaUsd.lib.PrimUpdaterManager.mergeToUsd(rigMayaPathAndOptions))
pxr.Tf.ErrorException:
	Error in 'pxrInternal_v0_22__pxrReserved__::UsdMaya_RegistryHelper::AddUnloader' at line 354 in file .../maya-usd/lib/mayaUsd/fileio/registryHelper.cpp : 'Couldn't add unload function (was this function called from outside a TF_REGISTRY_FUNCTION block?)'

======================================================================
ERROR: testEditAndMergeRigMayaRef (testCacheToUsd.CacheToUsdTestCase)
Test editing then merge a Maya Reference to a complex animated rig.
----------------------------------------------------------------------
Traceback (most recent call last):
  File ".../maya-usd/test/lib/mayaUsd/fileio/testCacheToUsd.py", line 499, in testEditAndMergeRigMayaRef
    self.assertTrue(mayaUsd.lib.PrimUpdaterManager.mergeToUsd(aMayaPathStr, userArgs))
pxr.Tf.ErrorException:
	Error in 'pxrInternal_v0_22__pxrReserved__::UsdMaya_RegistryHelper::AddUnloader' at line 354 in file .../maya-usd/lib/mayaUsd/fileio/registryHelper.cpp : 'Couldn't add unload function (was this function called from outside a TF_REGISTRY_FUNCTION block?)'

======================================================================
FAIL: testUsdPreviewSurfaceRoundtripMetallic (testUsdExportImportRoundtripPreviewSurface.testUsdExportImportRoundtripPreviewSurface)
----------------------------------------------------------------------
Traceback (most recent call last):
  File ".../maya-usd/test/lib/usd/translators/testUsdExportImportRoundtripPreviewSurface.py", line 65, in testUsdPreviewSurfaceRoundtripMetallic
    self.__testUsdPreviewSurfaceRoundtrip(metallic=True)
  File ".../maya-usd/test/lib/usd/translators/testUsdExportImportRoundtripPreviewSurface.py", line 218, in __testUsdPreviewSurfaceRoundtrip
    self.assertTrue(mark.IsClean())
AssertionError: False is not true

[seando-adsk]

@katpet Did you ever get a chance to look into the preflight test failures?

Sean