Improve non-first {% extends %} error message

[Adam Johnson]

Currently if you put {% extends %} after another tag, the error looks like:

TemplateSyntaxError: <ExtendsNode: extends 'base.html'> must be the first tag in the template.

ExtendsNode is a leaked internal detail. Showing its repr() is a bit confusing, especially for a beginner programmer.

The message would be clearer if it showed the actual text of the tag:

TemplateSyntaxError: {% extends 'base.html' %} must be the first tag in the template.

[Mohamed Nabil Rady]

So After looking at the code I am a bit stuck on what should be done, the error message is constructed using the __repr__ method of ExtendNode class

    # The way the error is constructed
    if node.must_be_first and nodelist.contains_nontext:
        raise self.error(
            token,
            "%r must be the first tag in the template." % node,
        )

And this is the __repr__ function

    # __repr__ function for ExtendsNode class
    def __repr__(self):
        return "<%s: extends %s>" % (self.__class__.__name__, self.parent_name.token)

I don't think changing the repr method or hard coding the error message is any better. So what should be done ?

[Adam Johnson]

The repr should not be changed, it’s still used in other contexts like debugging. Change the error message to show/build the extends tag source.

[Ekin Ertaç]

Just sent a PR to github to add a clear error message. ​PR

Edit:
I didn't notice the first PR, sorry about that.

[Sarah Boyce <42296566+sarahboyce@…>]

In 68cee15:

Fixed #35789 -- Improved the error message raised when the tag must be first in the template.