don't create a local variable with the name of the partial when no :local or :object option was passed

[jfirebaugh]

From this stack overflow question.

Suppose I have a partial _flash.html.erb for rendering the flash in a consistent way. The natural thing to do would be to assume I can call ActionView::Base#flash from within this partial to retrieve the flash, and render the partial with render partial: "flash". But in fact, this doesn't work. Even though I haven't passed object: flash or locals: {flash: flash} in the call to render partial, PartialRenderer oh-so-helpfully defines a flash local variable, whose value is nil, shadowing ActionView::Base#flash. My alternatives are to rename the partial or pass a value for the flash local explicitly using one of those more verbose call to render.

I suggest that if no object option or local with the same name as the partial was passed to the render call, that PartialRenderer not define a local variable of the same name as the partial. This would change the behavior for anyone who is relying on the current behavior to get a nil value for the local when they don't pass an explicit value, but that seems like an unlikely case and easily fixed by passing nil explicitly, and it would be much more useful to do things like call ActionView::Base#flash from within a _flash.html.erb partial.

I'm happy to create a pull request if others agree.

[steveklabnik]

We don't accept feature requests on the Issues tracker. Please either submit a pull request or ask for feedback on rails-core. Thanks.

[frodsan]

Also, reading CONTRIBUTING guide is a good start before posting an issue :)