Blacklight 7.x, deprecation of view overrides, paths forward

This post will only be of interest to those who use the blacklight ruby gem/platform, mostly my collagues in library/cultural heritage sector.

When I recently investigated updating our Rails app from Blacklight to the latest 7.19.2, I encountered a lot of deprecation notices. They were related to code both in my local app and a plugin trying to override parts of Blacklight views — specifically the “constraints” (ie search limits/query “breadcrumbs” display) area in the code I encountered, I’m not sure if it applies to more areas of view customization.

Looking into this more to see if I could get a start on changing logic to avoid deprecation warnings — I had trouble figuring out any non-deprecated way to achieve the overrides.  After more research, I think it’s not totally worked out how to make these overrides keep working at all in future Blacklight 8, and that this affects plugins including blacklght_range_limit, blacklight_advanced_search, geoblacklight, and possibly spotlight. Some solutions need to be found if these plugins are to be updated keep working in future Blacklight 8.

I have documented what I found/understood, and some ideas for moving forward, hoping it will help start the community process of figuring out solutions to keep all this stuff working. I may not have gotten everything right or thought of everything, this is meant to help start the discussion, suggestions and corrections welcome.

This does get wordy, I hope you can find it useful to skip around or skim if it’s not all of interest. I believe the deprecations start around Blacklight 7.12 (released October 2020). I believe Blacklight 7.14 is the first version to suport ruby 3.0, so anyone wanting to upgrade to ruby 3 will encounter these issues.


Over blacklight’s 10+ year existence, it has been a common use-case to customize specific parts of Blacklight, including customizing what shows up on one portion of a page while leaving other portions ‘stock’. An individual local application can do this with it’s own custom code; it is also common from many of shared blacklight “plug-in”/”extension” engine gems.

Blacklight had tradtionally implemented it’s “view” layer in a typical Rails way, involving “helper” methods and view templates. Customizations and overrides, by local apps or plugins, were implemented by over-riding these helper methods and partials. This traditional method of helper and partial overrides is still described in the Blacklight project wiki — it possibly could use updating for recent deprecations/new approaches).

This view/helper/override approach has some advantages: It just uses standard ruby and Rails, not custom Blacklight abstractions; multiple different plugins can override the same method, so long as they all call “super”, to cooperatively add funtionality; it is very flexible and allows overrides that “just work”.

It also has some serious disadvantages. Rails helpers and views are known in general for leading to “spaghetti” or “ball of mud” code, where everything ends up depending on everything/anything else, and it’s hard to make changes without breaking things.

In the context of shared gem code like Blacklight and it’s ecosystem, it can get even messier to not know what is meant to be public API for an override. Blacklight’s long history has different maintainers with different ideas, and varying documentation or institutional memory of intents can make it even more confusing. Several generations of ideas can be present in the current codebase for both backwards-compatibility and “lack of resources to remove it” reasons. It can make it hard to make any changes at all without breaking existing code, a problem we were experiencing with Blacklight.

One solution that has appeared for Rails is the ViewComponent gem (written by github, actually), which facilitates better encapsulation, separation of concerns, and clear boundaries between different pieces of view code.The current active Blacklight maintainers (largely from Stanford I think?) put in some significant work — in Blacklight 7.x — to rewrite some significant parts of Blacklight’s view architecture based on the ViewComponent gem. This is a welcome contribution to solving real problems! Additionally, they did some frankly rather heroic things to get this replacement with ViewComponent to be, as a temporary transition step, very backwards compatible, even to existing code doing extensive helper/partial overrides, which was tricky to accomplish and shows their concern for current users.

Normally, when we see deprecation warnings, we like to fix them, to get them out of our logs, and prepare our apps for the future version where deprecated behavior stops working entirely. To do otherwise is considered leaving “technical debt” for the future, since a deprecation warning is telling you that code will have to be changed eventually.

The current challenge here is that it’s not clear (at least to me) how to change the code to still work in current Blacklight 7.x and upcoming Blacklight 8x. Which is a challenge both for running in current BL 7 without deprecation, and for the prospects of code continuing to work in future BL 8. I’ll explain more with examples.

Blacklight_range_limit (and geoblacklight): Add a custom “constraint”

blacklight_range_limit introduces new query parameters for range limit filters, not previously recognized by Blacklight, that look eg like &range[year_facet][begin]=1910 In addition to having these effect the actual Solr search, it also needs to display this limit (that Blacklight core is ignoring) in the “constraints” area above the search results:

To do this it overrides the render_constraints_filters helper method from Blacklight, through some fancy code effectively calling super to render the ordinary Blacklight constraints filters but then adding on it’s rendering of the contraints only blacklight_range_limit knows about. One advantage of this “override, call super, but add on” approach is that multiple add-ons can do it, and they don’t interfere with each other — so long as they all call super, and only want to add additional content, not replace pre-existing content.

But overriding this helper method is deprecated in recent Blacklight 7.x. If Blacklight detects any override to this method (among other constraints-related methods), it will issue a deprecation notice, and also switch into a “legacy” mode of view rendering, so the override will still work.

OK, what if we wanted to change how blacklight_range_limit does this, to avoid triggering the deprecation warnings, and to have blacklight continue to use the “new” (rather than “legacy”) logic, that will be the logic it insists on using in Blacklight 8?

The new logic is to render with the new view_component, Which is rendered in the catalog/_constraints.html.erb partial. I guess if we want the rendering to behave differently in that new system, we need to introduce a new view component that is like Blacklight::ConstraintsComponent but behaves differently (perhaps a sub-class, or a class using delegation). Or, hey, that component takes some dependent view_components as args, maybe we just need to get the ConstraintsComponent to be given an arg for a different version of one of the _component args, not sure if that will do it.

It’s easy enough to write a new version of one of these components… but how would we get Blacklight to use it?

I guess we would have to override catalog/_constraints.html.erb. But this is unsastisfactory:

  • I thougth we were trying to get out of overriding partials, but even if it’s okay in this situation…
  • It’s difficult and error-prone for an engine gem to override partials, you need to make sure it ends up in the right order in Rails “lookup paths” for templates, but even if you do this…
  • What if multiple things want to add on a section to the “constraints” area? Only one can override this partial, there is no way for a partial to call super.

So perhaps we need to ask the local app to override catalog/_constraints.html.erb (or generate code into it), and that code calls our alternate component, or calls the stock component with alternate dependency args.

  • This is already seeming a bit more complex and fragile than the simpler one-method override we did before, we have to copy-and-paste the currently non-trivial implementation in _constraints.html.erb, but even if we aren’t worried about that….
  • Again, what happens if multiple different things want to add on to what’s in the “constraints” area?
  • What if there are multiple places that need to render constraints, including other custom code? (More on this below). They all need to be identically customized with this getting-somewhat-complex code?

That multiple things might want to add on isn’t just theoretical, geoblacklight also wants to add some things to the ‘constraints’ area and also does it by overriding the render_constraints_filters method.

Actually, if we’re just adding on to existing content… I guess the local app could override catalog/_constraints.html.erb, copy the existing blacklight implementation, then just add on the END a call to both say <%= render(BlacklightRangeLimit::RangeConstraintsComponent %> and then also <%= <%= render(GeoBlacklight::GeoConstraintsComponent) %>… it actually could work… but it seems fragile, especially when we start dealing with “generators” to automatically create these in a local app for CI in the plugins, as blacklight plugins do?

My local app (and blacklight_advanced_search): Change the way the “query” constraint looks

If you just enter the query ‘cats’, “generic” out of the box Blacklight shows you your search with this as a sort of ‘breadcrumb’ constraint in a simple box at the top of the search:

My local app (in addition to changing the styling) changes that to an editable form to change your query (while keeping other facet etc filters exactly the same). Is this a great UX? Not sure! But it’s what happens right now:

It does this by overriding `render_constraints_query` and not calling super, replace the standard implementation with my own.

How do we do this in the new non-deprecated way?

I guess again we have to either replace Blacklight::ConstraintsComponent with a new custom version… or perhaps pass in a custom component for query_constraint_component… this time we can’t just render and add on, we really do need to replace something.

What options do we? Maybe, again, customizing _constraints.html.erb to call that custom component and/or custom-arg. And make sure any customization is consistent with any customization done by say blacklight_range_limit or geoblacklight, make sure they aren’t all trying to provide mutually incompatible custom components.

I still don’t like:

  • having to override a view partial (when before I only overrode a helper method), in local app instead of plugin it’s more feasible, but we still have to copy-and-paste some non-trivial code from Blacklight to our local override, and hope it doesn’t change
  • Pretty sensitive to implementation of Blacklight::ConstraintsComponent if we’re sub-classing it or delegating it. I’m not sure what parts of it are considered public API, or how frequently they are to change… if we’re not careful, we’re not going ot have any more stable/reliable/forwards-compatible code than we did under the old way.
  • This solution doesn’t provide a way for custom code to render a constraints area with all customizations added by any add-ons, which is a current use case, see next section.

It turns out blacklight_advanced_search also customizes the “query constraint” (in order to handle the multi-field queries that the plugin can do), also by overriding render_constraints_query, so this exact use case affects that plug-in too, with a bit more challenge in a plugin instead of a local app.

I don’t think any of these solutions we’ve brainstormed are suitable and reliable.

But calling out to Blacklight function blocks too, as in spotlight….

In addition to overriding a helper method to customize what appears on the screen, traditionally custom logic in a local app or plug-in can call a helper method to render some piece of Blacklight functionality on screen.

For instance, the spotlight plug-in calls the render_constraints method in one of it’s own views, to include that whole “constraints” area on one of it’s own custom pages.

Using the legacy helper method architecture, spotlight can render the constraints including any customizations the local app or other plug-ins have made via their overriding of helper methods. For instance, when spotlight calls render_constraints, it will get the additional constraints that were added by blacklight_range_limit or geoblacklight too.

How would spotlight render constraints using the new architecture? I guess it would call the Blacklight view_component directly, render( But how does it manage to use any customizations added by plug-ins like blacklight_range_limit? Not sure. None of the solutions we brainstormed above seem to get us there.

I suppose (Eg) spotlight could actually render the constraints.html.erb partial, that becomes the one canonical standardized “API” for constraints rendering, to be customized in the local app and re-used every time constraints view is needed? That might work, but seems a step backwards to go toward view partial as API to me, I feel like we were trying to get away from that for good reasons, it just feels messy.

This makes me think new API might be required in Blacklight, if we are not to have reduction in “view extension” functionality for Blacklgiht 8 (which is another option, say, well, you just cant’ do those things anymore, significantly trimming the scope of what is possible with plugins, possibly abandoning some plugins).

There are other cases where blacklight_range_limit for example calls helper methods to re-use functionality. I haven’t totally analyzed them. It’s possible that in some cases, the plug-in just should copy-and-paste hard-coded HTML or logic, without allowing for other actors to customize them. Examples of what blacklight_range_limit calls here include

New API? Dependency Injection?

Might there be some new API that Blacklight could implement that would make this all work smoother and more consistently?

“If we want a way to tell Blacklight “use my own custom component instead of Blacklight::ConstraintsComponent“, ideally without having to override a view template, at first that made me think “Inversion of Control with Dependency Injection“? I’m not thrilled with this generic solution, but thinking it through….

What if there was some way the local app or plugin could do Blacklight::ViewComponentRegistration.constraints_component_class = MyConstraintsComponent, and then when blacklight wants to call it, instead of doing, like it does now, <%= render( stuff) %>, it’d do something like: `<%= stuff) %>.

That lets us “inject” a custom class without having to override the view component and every other single place it might be used, including new places from plugins etc. The specific arguments the component takes would have to be considered/treated as public API somehow.

It still doesn’t let multiple add-ons cooperate to each add a new constraint item though. i guess to do that, the registry could have an array for each thing….

Blacklight::ViewComponentRegistration.constraints_component_classes = [

# And then I guess we really need a convenience method for calling
# ALL of them in a row and concatenating their results....

Blacklight::ViewComponentRegistration.render(:constraints_component_class, search_state: stuff)

On the plus side, now something like spotlight can call that too to render a “constraints area” including customizations from BlacklightRangeLimit, GeoBlacklight, etc.

But I have mixed feelings about this, it seems like the kind of generic-universal yet-more-custom-abstraction thing that sometimes gets us in trouble and over-complexified. Not sure.

API just for constraints view customization?

OK, instead of trying to make a universal API for customizing “any view component”, what if we just focus on the actual use cases in front of us here? All the ones I’ve encountered so far are about the “constraints” area? Can we add custom API just for that?

It might look almost exactly the same as the generic “IoC” solution above, but on the Blacklight::ConstraintsComponent class…. Like, we want to customize the component Blacklight::ConstraintsComponent uses to render the ‘query constraint’ (for my local app and advanced search use cases), right now we have to change the call site for every place it exists, to have a different argument… What if instead we can just:

Blacklight::ConstraintsComponent.query_constraint_component =

And ok, for these “additional constraint items” we want to add… in “legacy” architecture we overrode “render_constraints_filters” (normally used for facet constraints) and called super… but that’s just cause that’s what we had, really this is a different semantic thing, let’s just call it what it is:

Blacklight::ConstraintsComponent.additional_render_components <<

Blacklight::ConstraintsComponent.additional_render_components <<

All those component “slots” would still need to have their initializer arguments be established as “public API” somehow, so you can register one knowing what args it’s initializer is going to get.

Note this solves the spotlight case too, spotlight can just simply call render Blacklight::ConstraintsComponent(..., and it now does get customizations added by other add-ons, because they were registered with the Blacklight::ConstraintsComponent.

I think this API may meet all the use cases I’ve identified? Which doesn’t mean there aren’t some I haven’t identified. I’m not really sure what architecture is best here, I’ve just trained to brainstorm possibilities. It would be good to choose carefully, as we’d ideally find something that can work through many future Blacklight versions without having to be deprecated again.

Need for Coordinated Switchover to non-deprecated techniques

The way Blacklight implements backwards-compatible support for the constraints render, is if it detects anything in the app is overriding a relevant method or partial, it continues rendering the “legacy” way with helpers and partials.

So if I were to try upgrading my app to do something using a new non-deprecatred method, while my app is still using blacklight_range_limit doing things the old way… it woudl be hard to keep them both working. If you have more than one Blacklight plug-in overriding relevant view helpers, it of course gets even more complicated.

It pretty much has to be all-or-nothing. Which also makes it hard for say blacklight_range_limit to do a release that uses a new way (if we figured one out) — it’s probably only going to work in apps that have changed ALL their parts over to the new way. I guess all the plug-ins could do releases that offered you a choice of configuration/installation instructions, where the host app could choose new way or old way.

I think the complexity of this makes it more realistic, especially based on actual blacklight community maintenance resources, that a lot of apps are just going to keep running in deprecated mode, and a lot of plugins only available triggering deprecation warnings, until Blacklight 8.0 comes out and the deprecated behavior simply breaks, and then we’ll need Blacklight 8-only versions of all the plugins, with apps switching everything over all at once.

If different plugins approach this in an uncoordianted fashion, each trying to investnt a way to do it, they really risk stepping on each others toes and being incompatible with each other. I think really something has to be worked out as the Blacklgiht-recommended consensus/best practice approach to view overrides, so everyone can just use it in a consistent and compatible way. Whether that requires new API not yet in Blacklight, or a clear pattern with what’s in current Blacklight 7 releasees.

Ideally all worked out by currently active Blacklight maintainers and/or community before Blacklight 8 comes out, so people at least know what needs to be done to update code. Many Blacklight users may not be using Blacklight 7.x at all yet (7.0 released Dec 2018) — for instance hyrax still uses Blacklight 6 — so I’m not sure what portion of the community is already aware this is coming up on the horizon.

I hope the time I’ve spent investigating and considering and documenting in this piece can be helpful to the community as one initial step, to understanding the lay of the land.

For now, silence deprecations?

OK, so I really want to upgrade to latest Blacklight 7.19.2, from my current 7.7.0. To just stay up to date, and to be ready for ruby 3.0. (My app def can’t pass tests on ruby 3 with BL 7.7; it looks like BL added ruby 3.0 support in BL 7.14.0? Which does already have the deprecations).

It’s not feasible right now to eliminate all the deprecated calls. But my app does seem to work fine, just with deprecation calls.

I don’t really want to leave all those “just ignore them for now”. deprecation messages in my CI and production logs though. They just clutter things up and make it hard to pay attention to the things Iwant to be noticing.

Can we silence them? Blacklight uses the deprecation gem for it’s deprecation messages; the gem is by cbeer, with logic taken out of ActiveSupport.

We could wrap all calls to deprecated methods in Deprecation.silence do…. including making a PR to blacklight_range_limit to do that? I’m not sure I like the idea of making blacklight_range_limit silent on this problem, it needs more attention at this point! Also I’m not sure how to use Deprecation.silence to effect that clever conditional check in the _constraints.html.erb template.

We could entirely silence everything from the deprecation gem with Deprecation.default_deprecation_behavior — I don’t love this, we might be missing deprecations we want?

The Deprecation gem API made me think there might be a way to silence deprecation warnings from individual classes with things like Blacklight::RenderConstraintsHelperBehavior.deprecation_behavior = :silence, but I think I was misinterpreting the API, there didn’t seem to be actually methods like that available in Blacklight to silence what I wanted in a targetted way.

Looking/brainstormign more in Deprecation gem API… I *could* change it’s behavior to it’s “notify” strategy that sends ActiveSupport::Notification events instead of writing to stdout/log… and then write a custom ActiveSupport::Notification subscriber which ignored the ones I wanted to ignore… ideally still somehow keeping the undocumented-but-noticed-and-welcome default behavior in test/rspec environment where it somehow reports out a summary of deprecations at the end…

This seemed too much work. I realized that the only things that use the Deprecation gem in my project are Blacklight itself and the qa gem (I don’t think it has caught on outside blacklight/samvera communities), and I guess I am willing to just silence deprecations from all of them, although I don’t love it.


One thought on “Blacklight 7.x, deprecation of view overrides, paths forward

  1. Another use case I just ran into, which would be good to consider how to handle under new architecture:

    I want all my sidebar facet limit links to have a “nofollow” attribute. (I think this is probably a good general use case, I think it often makes sense?)

    There is a certain deprecated way to do it under “old” architecture — over-riding the “render_facet_value”, although it doens’t work really cleanly, you might have to copy-and-paste a lot of BL code.

    But how might I do do it new BL non-deprecated view architecture? Have my app override this default facet display to add “nofollow”? Is it possible/feasible/easy? I don’t know, or know how to do it.

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