Should we be applying the ThemeTransform on FilesystemFile?

[frapell]

I am having an issue with a theme that defines some [theme:parameters] and a request that tries to get a plone.resource.file.FilesystemFile, such as Mosaic trying to get the Basic layout (Somethig like http://localhost:8080/Plone/++contentlayout++default/basic.html)

This particular issue happens in

plone.app.theming/src/plone/app/theming/transform.py

Lines 175 to 180 in d2fe5c1

	params = prepareThemeParameters(
	findContext(self.request),
	self.request,
	parameterExpressions,
	cache
	)

where findContext(self.request) would return a <FilesystemResourceDirectory object at default>

and so, you would get a zExceptions.NotFound

This can be reproduced by adding

[theme:parameters]
url = context/absolute_url

in plonetheme/barceloneta/theme/manifest.cfg and reapplying the theme. So when trying to edit a mosaic page you will get a generic Error loading layout specified for this content. Falling back to basic layout. which loops forever. And you can see in the terminal

2022-04-13 11:15:42,717 ERROR   [plone.transformchain:69][waitress-0] Unexpected error whilst trying to apply transform chain
Traceback (most recent call last):
  File "/trabajo/plone/buildout.coredev/eggs/plone.transformchain-2.0.2-py3.8.egg/plone/transformchain/transformer.py", line 59, in __call__
    newResult = handler.transformIterable(result, encoding)
  File "/trabajo/plone/buildout.coredev/eggs/plone.app.theming-5.0.0a5-py3.8.egg/plone/app/theming/transform.py", line 175, in transformIterable
    params = prepareThemeParameters(
  File "/trabajo/plone/buildout.coredev/eggs/plone.app.theming-5.0.0a5-py3.8.egg/plone/app/theming/utils.py", line 778, in prepareThemeParameters
    params[name] = quote_param(expression(expressionContext))
  File "/trabajo/plone/buildout.coredev/eggs/zope.tales-5.1-py3.8.egg/zope/tales/expressions.py", line 250, in __call__
    return self._eval(econtext)
  File "/trabajo/plone/buildout.coredev/src/Zope/src/Products/PageTemplates/Expressions.py", line 213, in _eval
    ob = self._subexprs[-1](econtext)
  File "/trabajo/plone/buildout.coredev/eggs/zope.tales-5.1-py3.8.egg/zope/tales/expressions.py", line 153, in _eval
    ob = self._traverser(ob, element, econtext)
  File "/trabajo/plone/buildout.coredev/src/Products.CMFPlone/Products/CMFPlone/earlypatches/expressions.py", line 173, in boboAwareZopeTraverse
    result = shared_traverse(object, path_items, request)
  File "/trabajo/plone/buildout.coredev/src/Products.CMFPlone/Products/CMFPlone/earlypatches/expressions.py", line 114, in shared_traverse
    found = traversePathElement(base, name, path_items,
  File "/trabajo/plone/buildout.coredev/eggs/zope.traversing-4.4.1-py3.8.egg/zope/traversing/adapters.py", line 156, in traversePathElement
    return traversable.traverse(nm, further_path)
  File "/trabajo/plone/buildout.coredev/eggs/zope.traversing-4.4.1-py3.8.egg/zope/traversing/adapters.py", line 58, in traverse
    return subject[name]
  File "/trabajo/plone/buildout.coredev/eggs/plone.resource-2.1.4-py3.8.egg/plone/resource/directory.py", line 252, in __getitem__
    return self.publishTraverse(None, name)
  File "/trabajo/plone/buildout.coredev/eggs/plone.resource-2.1.4-py3.8.egg/plone/resource/directory.py", line 244, in publishTraverse
    raise NotFound
zExceptions.NotFound

I believe there is no use in applying the ThemeTransform when returning a file from the filesystem. (As a side effect we would get a faster response time for resources).

Now, I am not 100% sure which Interface should be better to adapt. I've replaced Interface with ILocation (from zope.location.interfaces.ILocation) in @adapter(ILocation, IThemingLayer) and it does fix the issue, but I am not entirely sure if this is the Interface I should be using.

So, is this a desired change? if so, do you have a better suggestion on which Interface to use?

[frapell]

@mauritsvanrees @petschki @thet @MrTango @pbauer Thoughts?

[mauritsvanrees]

I would expect the theme transform to be run on all files. Well, on Page Templates anyway. But really anything with html.

I wonder if it would help if the theme transform does not run on subrequests, or if that has unwanted side effects.

[frapell]

@mauritsvanrees Mmmh, I see your point, however it shouldn't fail, even on a direct request to the resource... Maybe what needs to be fixed then is the findContext(self.request) ?