fix(URI template): allow complex vars coexist with simple var

[philiptzou]

Allow situation like this:

api.add_route('/files/{file_id}', resource_1)
api.add_route('/files/{file_id}.{ext}', resource_2)

Which ValueError was raised due to only one var node was allowed whether
other nodes are complex or not. This fix changes the behaviour so now it
only applys to simple vars.

See #564

[philiptzou]

So {file_id} is a simple var, but {file_id}.{ext} is a complex var (which is converted to compiled regexp).

[yohanboniface]

Humm, actually, two remarks:

• with this patch, we can register /compare/{file_id}/ then /compare/{file_id}.{ext}/, but not the other way around; given that nodes are then reordered, I'm not sure the order we register the routes should have importance, but I may be wrong
• we can now register /compare/{file_id}.{ext}/ then /compare/{file_name}.{ext}/which should conflict in reality IMHO

[yohanboniface]

we can now register /compare/{file_id}.{ext}/ then /compare/{file_name}.{ext}/ which should conflict in reality IMHO

This was already the case before sorry. Is that on purpose, @kgriffs?

[yohanboniface]

OK, complex means also {usr0}:{branch0}...{usr1}:{branch1} vs {usr0}:{branch0}, so it seems we don't want to enter in trying to detect complex nodes conflicts (and thus order they are registered is important).

[philiptzou]

@yohanboniface Good point on the complex nodes conflicts! 👍 I think I have a simple way to detect such conflicts before we feed them to the compiled router. But perhaps in another pull-request.

[philiptzou]

@yohanboniface The registering order is not important since we'll sort the nodes inside our code. That's here. Before this case, static nodes (for example /foo/bar) are always sorted before var nodes (/foo/{var}).

So put '/compare/{file_id}' after/before '/compare/{file_id}.{ext}' are both acceptable and the results are the same.

[yohanboniface]

humm, but then this should work equally, right?

In [1]: from falcon.routing import DefaultRouter; router = DefaultRouter()

In [2]: router.add_route('/files/{file_id}', {}, 'xxxx2')

In [3]: router.add_route('/files/{file_id}.{ext}', {}, 'xxxx2')

In [1]: from falcon.routing import DefaultRouter; router = DefaultRouter()

In [2]: router.add_route('/files/{file_id}.{ext}', {}, 'xxxx2')

In [3]: router.add_route('/files/{file_id}', {}, 'xxxx2')
ValueError: The URI template for this route conflicts with another route's template.

[philiptzou]

Btw, I think we can simply detect conflicts amongst complex nodes like this:

import re

def is_conflict(complex_nodes):
    pseudo_segments = [re.sub(r'({[-_a-zA-Z0-9]+})', '{v}', n.raw_segment)
                       for n in complex_nodes]
    return len(set(pseudo_segments)) < len(pseudo_segments)

Perhaps another pull-request, @kgriffs? (Update see below)

[philiptzou]

@yohanboniface Good catch on the collision problem. See if the new revision I just submitted fix the issue you encountered.

[yohanboniface]

@philiptzou excellent! Your last commit fixes both collision issue and order issue :)

@kgriffs LGTM

[yohanboniface]

(@philiptzou your should rebase the branch on master, github says there are conflicts ;) )

[philiptzou]

@yohanboniface Well, I'll rebase after @kgriffs reviewed this. I have a feeling that he will find something too.

Have done the rebasing.

[kgriffs]

@philiptzou Nice work, LGTM! Could you please rebase once more and then I think this is ready to merge.

[philiptzou]

@kgriffs Done :)

[kgriffs]

@philiptzou Thanks! And thanks @yohanboniface for reviewing!