Aymeric, we have a difference of opinion. I feel that if {% include %}
removed the trailing newline, it would result in far more intuitive
whitespace control (which may be needed in plain text email templates, for
example). I think the change has merits outside the context of this issue.
For example, I checked view-source on a djangoproject.com page that uses a
{% for ... %}{% include %}{% endfor %} construct and noticed that it's much
shorter without all those extra blank lines. I'm not advocating for
additional controls to craft well formatted HTML but I think there's some
advantages to not having blank lines everywhere. (I don't like the
keep_trailing_newline option either, I'd rather call it a bugfix and make a
backwards-incompatible change but my projects are unaffected as far as I
checked.)
There are many questions on Stackoverflow about how to suppress newlines
from {% include %} and even a django-include-strip-tag third-party app that
offers the feature.
In the context of multiple template engines, I think it would be useful if
DTL templates could be written in a similar style to Jinja2.
I'd like to know from Carl, Adam, and others, how much effort would be
required to adapt the templates in your project for the new behavior. I
imagine a script could be written to add newlines after all {% include %}
in all plain text templates, for example.
It won't be the end of the world if we can't get consensus to change the
behavior -- I'm okay with removing the trailing newlines in the source
files as needed, although it will add some inconvenience.
On Wednesday, January 4, 2017 at 4:26:43 PM UTC-5, Aymeric Augustin wrote:
>
> If I understand correctly, we have to choose between:
>
> 1. breaking backwards compatibility for {% include %}
> 2. breaking backwards compatibility for widgets HTML
> 3. having a handful of single-line, non-newline-terminated files
>
> I don’t think option 1 is reasonable. Whitespace control in templates is
> an exercise in frustration. In my experience more flexible tools such as
> {%-, {%+, -%}, and +%} in Jinja2 increase the frustration. I don’t think
> Django should get itself into this mess just for fixing the problem
> discussed here.
>
> Option 2 seems acceptable to me. This is the "do nothing” option. I don’t
> think the exact HTML string rendered by widgets is considered a public API.
> We made changes to that output in the past, for example when we switched to
> HTML5.
>
> Option 3 also seems reasonable to me. Files could end with {# no newline,
> see issue #xxx #} and no newline. A test could validate that the rendered
> output doesn’t contain a newline. This would be enough to catch accidental
> regressions caused by editors automatically adding the newline.
>
> The quote from the POSIX standard says “should”, not “must”. If we
> interpret it as if it was written in capitals in a RFC, this means we can
> make an exception if we have a good reason.
>
> (At this point surely someone will suggest that we can write an
> editorconfig to specify that these files mustn’t end with a newline.
> Whatever works.)
>
> I don’t have a strong preference for 2 or 3, however, I have a strong
> distaste for anything more complicated.
>
> Best regards,
>
> --
> Aymeric.
>
> On 4 Jan 2017, at 20:58, Tim Graham <[email protected] <javascript:>>
> wrote:
>
> 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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