Add a system check to ensure "string_if_invalid" is a string

[JOSEPH KIM]

template option "string_if_invalid" cannot find error location with including html

for example

index.html

...
{% include "inc_home.html" %}
...

and inc_home.html has an invalid variable, Dajngo raise error at the beginning of index.html

work fine with {% extends %}

[Tim Graham]

I can't reproduce this given the information you provided. Could you provide a complete example as a sample project or as a test case for Django's test suite (tests/template_tests)?

[Tim Graham]

What version of Django are you using? On Django 1.8.x and Django 1.9.x, the sample project is crashing with:

  File "/home/tim/code/django/django/template/base.py", line 1043, in render
    output = self.filter_expression.resolve(context)
  File "/home/tim/code/django/django/template/base.py", line 716, in resolve
    if '%s' in string_if_invalid:
TypeError: argument of type 'bool' is not iterable

If I change the value to a string, e.g. 'string_if_invalid': 'fooo',, I'm seeing that value in the homepage output.

[JOSEPH KIM]

Replying to timgraham:

What version of Django are you using? On Django 1.8.x and Django 1.9.x, the sample project is crashing with:

  File "/home/tim/code/django/django/template/base.py", line 1043, in render
    output = self.filter_expression.resolve(context)
  File "/home/tim/code/django/django/template/base.py", line 716, in resolve
    if '%s' in string_if_invalid:
TypeError: argument of type 'bool' is not iterable

If I change the value to a string, e.g. 'string_if_invalid': 'fooo',, I'm seeing that value in the homepage output.

1.9.4 and it's intended error. Because, Django raised error but not indicate appropriate location in code if html file is included.

[Tim Graham]

string_if_invalid must be a string, not a boolean. We could add a system check to catch this mistake.

[Tim Graham]

Left comments for improvement.

[Tim Graham <timograham@…>]

In abf0735:

Fixed #26365 -- Added a system check to ensure "string_is_invalid" is a string.