Component templates set variables in outer scope

[lfdebrux]

Description of issue

The radios component template sets variables from an outer scope with the expectation that the value will be available later in the outer scope[2].

The Jinja template language has strict rules on the scope of variables; by default blocks cannot access variables set in outer scopes[1]. This is inline with the scoping behaviour of Python (as opposed to the scoping behaviour of JavaScript, which makes variables global by default).

The Jinja documentation is clear that setting variables in an outer scope will not work[3]. The suggested workaround is to use a namespace object.

Affected components

• checkboxes
• date-input
• file-upload
• radios
• text-area

Possible workaround

Change the component templates to use a namespace object when setting a variable in an outer scope.

[lfdebrux]

#8 fixes this by patching the template; see the commit.

The regex rule for this is a little frustrating, because we have to substitute all instances of requiredBy when it actually means the nonlocal variable, but avoid instances where it's actually a different variable.

There may be a better option, perhaps by adding an extension that lets us use the Python global or nonlocal statements?