Allow to create content with index_html id on the site root.

[thet]

First this needs to be merged in order to get the z3c.dependencychecker check green:
#108

The portal root has a index_html method which prevented content with the id index_html to be created and used as a default page.

Fixes: plone/Products.CMFPlone#4278

• I signed and returned the Plone Contributor Agreement, and received and accepted an invitation to join a team in the Plone GitHub organization.
• I verified there aren't any other open pull requests for the same change.
• I followed the guidelines in Contributing to Plone.
• I successfully ran code quality checks on my changes locally.
• I successfully ran tests on my changes locally.
• If needed, I added new tests for my changes.
• If needed, I added documentation for my changes.
• I included a change log entry in my commits.

---

If your pull request closes an open issue, include the exact text below, immediately followed by the issue number. When your pull request gets merged, then that issue will close automatically.

Closes plone/Products.CMFPlone#4278

[mister-roboto]

@thet thanks for creating this Pull Request and helping to improve Plone!

TL;DR: Finish pushing changes, pass all other checks, then paste a comment:

@jenkins-plone-org please run jobs

To ensure that these changes do not break other parts of Plone, the Plone test suite matrix needs to pass, but it takes 30-60 min. Other CI checks are usually much faster and the Plone Jenkins resources are limited, so when done pushing changes and all other checks pass either start all Jenkins PR jobs yourself, or simply add the comment above in this PR to start all the jobs automatically.

Happy hacking!

[davisagli]

@thet Do things actually work once the item is created? My recollection is that traversal will find attributes (i.e. the index_html method on PloneSite) before it looks for subitems using getitem. That's the main reason that this code tries to prevent using names that would be found as attributes.

[thet]

@davisagli yes, it works - the index_html method of the portal object is called but that line gets the content item and returns it.

I'm preparing another PR in CMFPlone which removes line below which sets __replaceable__ attribute, which in turn invokes a plone.protect write-on-read confirmation message.