Avoid an edge case where content types would end up without fields

[frapell]

This fixes gh-165

[mister-roboto]

@frapell 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!

[frapell]

@jenkins-plone-org please run jobs

[frapell]

@jenkins-plone-org please run jobs

[frapell]

An alternative to this fix (to not mess with the result of the _p_mtime) would be to change the replacements made by

plone.dexterity/plone/dexterity/schema.py

Line 296 in a4ddc23

class SchemaNameEncoder(object):

to not hit this issue...

[jensens]

@jenkins-plone-org please run jobs

[jensens]

Actually this one would be nice to get merged. I updated the branch, but I have no idea why this breaks tests in plone.restapi.

[frapell]

@jensens Thanks for moving it forward! It's been so long I don't quite remember 😅 I'll try to take a look this weekend