form_for silently failing with rails 3.0.0

As far as I can tell, the form is just not appearing. No deprecation warnings in the logs.

This is with an explicit require to rails 3.0.0 in the Gemfile. Let me know what other info I can provide.

When using HAML as the template engine, I got the following error:

form_for outputs directly to the Haml template.
Disregard its return value and use the - operator,
or use capture_haml to get the value as a String.

It worked fine on the old rails 3-0-stable branch, but now it breaks on both 3-0-stable and 3.0.0 release. Master branch is still fine. I haven't gotten time to perform a diagnose yet, so I'm just pasting the error output here for reference.

Same here. Form just doesn't render. No warning, no error, nothing!

Problem occurs as soon as haml is added to the Gemfile.

To reproduce:
new rails project with simple scaffold -> works
add "gem 'haml'" to Gemfile -> form_for fails silently

Confirmed.

Nice wolax. Posted here: http://github.com/nex3/haml/issues/issue/249

Still not sure why master is fine.

Looks like that github issue is a dupe of http://github.com/nex3/haml/issues#issue/248

Confirmed Wolax's described behaviour

Found the potential source of the problem.

It seems like a bad case of copy-pasta gone wrong in the haml gem; the form_for method is defined twice, and the latter seems to be outdated.
Removing the latter definition makes everything work again (as far as I can tell) in both erb and haml templates.

(Attaching the diff file that fixes it)

I just got home, and I'm now looking into this. I hope to release Haml 3.0.18 with a fix some time tonight.

This has been fixed by http://github.com/nex3/haml/commit/61a1de3ff75e98e92688f9dd2d121a3c.... The fix is released as part of Haml 3.0.18.