Hey Tim,
I just wanted to mention that another approach for a transition plan could
be
to use {% load include from future %} like we did with the {% url %} tag.
That doesn't answer the question of whether or not we should make the change
but I think it offers a better upgrade path than a global template option or
a keep_trailing_newline kwarg.
Simon
Le mercredi 4 janvier 2017 14:58:42 UTC-5, Tim Graham a écrit :
>
> Shortly after template widget rendering was merged, an issue about extra
> newlines appearing in the rendered output was reported [0]:
>
> For example, from django-money:
>
> <option value="XFU" \n>UIC-Franc</option>
> \n\n
> <option value="USD" selected\n>US Dollar</option>
> \n\n
>
> The newlines aren't useful and they break assertions like this:
>
> <option value="USD" selected>US Dollar</option> in form.as_p
>
> --- end report---
>
> The reporter suggested removing the trailing newline in the attrs.html
> template but Adam Johnson reported: "POSIX states that all text files
> should end with a newline, and some tools break when operating on text
> files missing the final newline. That's why git has the warning \ No
> newline at end of file and Github has a warning symbol for the missing
> newline."
>
> I suggested that perhaps {% include %} could do .rstrip('\n') on whatever
> it renders.
>
> Preston pointed out that Jinja2 does something similar:
>
> http://jinja.pocoo.org/docs/dev/templates/#whitespace-control
>
> - a single trailing newline is stripped if present
> - other whitespace (spaces, tabs, newlines etc.) is returned unchanged
>
> I noted that the issue of {% include %} adding extra newlines was raised
> in #9198 [1] but Malcolm said, "For backwards compatibility reasons we
> cannot change the default behaviour now (there will be templates that rely
> on the newline being inserted)." I was skeptical this would be a burdensome
> change.
>
> Carl replied: "It seems quite likely to me that there are templates in
> the wild relying on preservation of the final newline. People render
> preformatted text (e.g. text emails) using DTL. I probably have some text
> email templates in older projects myself that would break with that change.
>
> We could add a new option to {% include %}, though." Adam also said, "I
> too have used DTL for text emails that would break under that behaviour.
> New option to include sounds good to me."
>
>
> Me again: In the long run, having {% include %} remove the trailing
> newline seems like a more sensible default. For example, I wouldn't expect
> this code to have a newline inserted between it:
>
>
> {% include "foo.txt" %}
> {% include "bar.txt" %}
>
>
> An option for {% include %} seems superfluous given that if you were
> writing
>
>
> {% include "foo.txt" %}{% include "bar.txt" %}
>
>
> now you can write the first thing which is much more intuitive.
>
>
> How about a keep_trailing_newline TEMPLATES option for backwards
> compatibility for those who don't want to adapt their templates for the new
> behavior? Jinja2 has that option.
>
> Carl replied: An engine option may be better than an option to {% include
> %}, though it doesn't allow us to ensure that we strip the newline in the
> specific case of attrs.
>
> How we default the engine option I guess just depends on how seriously we
> take backwards compatibility. If we default it to strip and make people add
> the config to preserve the old behavior, that's not really backwards
> compatible. Historically (as seen in Malcolm's comment) we would choose to
> err on the side of actual backwards compatibility in a case like this, even
> if it didn't result in the ideal future behavior. But the adaptation isn't
> hard in this case, so I won't object if the choice is to break back-compat.
>
>
> If it's not a per-include choice, of course, we have to break overall
> back-compat to preserve form-attr-rendering back-compat.
> ----
>
> What do you think?
>
> [0] https://github.com/django/django/pull/7769
> [1] https://code.djangoproject.com/ticket/9198
>
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