Atualizando Discourse para Zeitwerk

Dev
1

O Rails 6 vem com dois modos de carregamento automático: zeitwerk e classic. Naquele pull request DEV: Upgrading Discourse to Rails 6 by KrisKotlarek · Pull Request #8083 · discourse/discourse · GitHub, atualizei o Rails para a versão 6.0.0 com o carregador automático clássico como uma fase transitória. Seria interessante tentar migrar para o Zeitwerk.

O Zeitwerk é um carregador de código eficiente e seguro para threads em Ruby. Desde que o projeto siga as convenções de nomenclatura, o Zeitwerk consegue encontrar os arquivos corretos e carregá-los sob demanda ou antecipadamente, sem a necessidade de qualquer require ou require_dependency. Além disso, conforme mencionado naquele artigo https://weblog.rubyonrails.org/2019/2/22/zeitwerk-integration-in-rails-6-beta-2/, ele pode oferecer um pequeno aumento de desempenho para a aplicação.

Existem algumas etapas que preciso realizar para fazê-lo funcionar:

  1. Alterar o nome de algumas classes para seguir a convenção de nomenclatura do Rails. Por exemplo, o arquivo canonical_url.rb deve definir a classe CanonicalUrl em vez de CanonicalURL. Da mesma forma, o arquivo ondiff.rb deve definir a classe Onpdiff em vez de ONPDiff. Uma abordagem alternativa seria conectar um inflector personalizado ao projeto; no entanto, acredito que seguir a convenção seja uma escolha melhor — GitHub - fxn/zeitwerk: Efficient and thread-safe code loader for Ruby · GitHub

  2. Similar ao ponto anterior, por convenção, validações personalizadas localizadas no diretório validations devem ser envoltas pelo módulo Validations. Além disso, algumas validações herdam de EachValidator e devem ser acessíveis sem namespace. Planejo movê-las para um diretório separado e adicioná-las aos caminhos de carregamento automático.

  3. Remover todos os require_dependency e garantir que o projeto esteja funcionando.

  4. Remover todos os require e garantir que o Discourse esteja funcionando.

  5. Garantir que todos os plugins possam acessar as dependências necessárias. Ainda não sei como alcançar isso. Quero primeiro fazer o Discourse funcionar sem nenhum plugin.

Claro, ainda há muitas incógnitas a resolver. Manterei você atualizado sobre o progresso; no entanto, se você tiver interesse em acompanhar, comecei a experimentar isso aqui: Commits · KrisKotlarek/discourse · GitHub

Por favor, me avise se você identificar alguma desvantagem na implementação do Zeitwerk ou se acha que deixei algo passar.

2

I made some progress around Zeitwerk, however, I changed my approach. My original plan was to change every place where Discourse is not following the Zeitwerk filename convention. After a few fixes, I realised that this is just the tip of the iceberg and noticed that if I am going to follow that path, then pull request will be difficult to read and confidently merge to master. For example, all job classes under regular directory should have Regular namespace, same with Onceoff and Scheduled.

I decided to step back a little bit and think about a more evolutionary approach than revolutionary.

I decided that it would be better to introduce custom Inflector, which will cover all files which are not following Zeitwerk convention. The biggest benefit will be that we would be able to deploy that small change and once we are happy with Zeitwerk and we don’t have any performance downgrades, we can start fixing convention file by file in reasonable small pull requests.

I found some problems which could not be sorted by custom Inflector, so I made additional fixes to make it work.

Pull request is still in progress, however, at this stage, I can run Discourse with Zeitwerk and default plugins, run all specs and run benchmark without a problem.

I wanted first to be at that stable state when all specs are passing. Now I can confidently start removing all require_dependency one by one and also test official plugins. Once everything is ready, I will share with you benchmark results in this post.

For now, if you are interested in progress you may take a look on that draft PR - DEV: Upgrading Discourse to Zeitwerk by KrisKotlarek · Pull Request #8098 · discourse/discourse · GitHub

The most important file is that custom Zeitwerk Inflector - DEV: Upgrading Discourse to Zeitwerk by KrisKotlarek · Pull Request #8098 · discourse/discourse · GitHub

3

To make plugins work I needed to create a few more small pull requests. Once they are merged I think that specs on Discourse should pass.

I also checked performance on Rails 6.0.0 with Classic autoloader and Rails 6.0.0 with Zeitwerk.

Test Classic Zeitwerk Percent
categories-50 32 26 81.25
categories-75 37 29 78.38
categories-90 47 35 74.47
categories-99 67 49 73.13
home-50 30 29 96.67
home-75 37 31 83.78
home-90 44 40 90.91
home-99 67 52 77.61
topic-50 35 35 100.00
topic-75 36 36 100.00
topic-90 48 36 75.00
topic-99 57 58 101.75
categories_admin-50 51 48 94.12
categories_admin-75 62 50 80.65
categories_admin-90 89 66 74.16
categories_admin-99 135 101 74.81
home_admin-50 48 47 97.92
home_admin-75 58 49 84.48
home_admin-90 67 64 95.52
home_admin-99 101 81 80.20
topic_admin-50 48 48 100.00
topic_admin-75 55 49 89.09
topic_admin-90 63 65 103.17
topic_admin-99 92 69 75.00
load_rails 2617 2165 82.73
rss_kb 282428 315684 111.78
pss_kb 270491 303504 112.20

Results are not always consistent so I would take them with a grain of salt.

4

The amount of inconsistency on the median here is a bit odd, I wonder why results are fluctuating so much

Surprised loader would have any impact

5

I tried it once again, here are results

Test Classic Zeitwerk Percent
categories-50 25 25 100.00
categories-75 26 26 100.00
categories-90 37 33 89.19
categories-99 57 48 84.21
home-50 26 26 100.00
home-75 27 28 103.70
home-90 38 35 92.11
home-99 60 50 83.33
topic-50 27 26 96.30
topic-75 35 27 77.14
topic-90 41 33 80.49
topic-99 54 50 92.59
categories_admin-50 48 50 104.17
categories_admin-75 60 61 101.67
categories_admin-90 76 71 93.42
categories_admin-99 122 122 100.00
home_admin-50 47 46 97.87
home_admin-75 58 55 94.83
home_admin-90 66 63 95.45
home_admin-99 99 121 122.22
topic_admin-50 50 49 98.00
topic_admin-75 62 50 80.65
topic_admin-90 72 65 90.28
topic_admin-99 103 74 71.84
load_rails 2675 2216 82.84
rss_kb 279924 315240 112.62
pss_kb 267659 303026 113.21

We can try another way to benchmark. What would you say about more iterations, something which would run for an hour? In addition, instead of taking the best result, compare the average from each experiment. That may give more consistent numbers. What do you think?

6

In my pull requests for plugins, you will notice that a lot of fixes are around searching in the global namespace.

I changed code like

module ::Jobs
  class TranslatorMigrateToAzurePortal < Jobs::Onceoff

to

module ::Jobs
  class TranslatorMigrateToAzurePortal < ::Jobs::Onceoff

One thing bothered me about that solution, why was it working before Zeitwerk. That question when something works but shouldn’t is always tricky :slight_smile:

I think I found a potential answer in the description of the classic autoloader (https://guides.rubyonrails.org/autoloading_and_reloading_constants_classic_mode.html#resolution-algorithms) - “If not found, then the algorithm walks up the ancestor chain of the cref”

Zeitwerk is more strict. Once I tried to load code before fix it was complaining that Jobs::Jobs::Onceoff can not be found.

Sam suggested under pull request FIX: Use top-level namespace for base classes · discourse/discourse-prometheus-alert-receiver@ef9c238 · GitHub, that instead of using < ::Jobs::Onceoff we can just use < Onceoff and he is right. I checked that without namespace it works as well. I am thinking that giving :: is explicitly saying that we are inheriting from Discourse Core class, however, we can go either way.

7

I think that when the code is this close together, this reads great:

module ::Jobs
  class TranslatorMigrateToAzurePortal < Onceoff

If the code starts floating down being explicit makes more sense … eg:

module ::Jobs
  [ 50 lines omitted]
  class TranslatorMigrateToAzurePortal < ::Jobs::Onceoff

That said, I am on a fence here, so I am fine either way. ::Jobs::Onceoff is short enough and mega explicit so we can just go with that for now.

8

I would love to start getting this merged. @kris.kotlarek is this now in a merge-able state? Timing is quite good cause we just had a beta

10

Let me rebase recent master into that and ensure that it still works, I will do that today

11

@sam I think we are good to go, I rebased with the latest master and made a small adjustment to Webauthn.
I checked 3 things:
run the server on local and click a little bit to ensure it works as expected
run specs
downloaded all official plugins and ensured that specs for plugins are passing (we need to merge adjustments for plugins first)

12

Cool I am merging this. Let’s see what shakes out!

13

Can we merge fixes for plugins as well? Otherwise, if you try to run Discourse with plugins it will fail

https://github.com/discourse/discourse-canned-replies/pull/51
https://github.com/discourse/discourse-cakeday/pull/29
https://github.com/discourse/discourse-voting/pull/45
https://github.com/discourse/discourse-perspective-api/pull/4
https://github.com/discourse/discourse-calendar/pull/4
https://github.com/discourse/discourse-prometheus/pull/4

14

Please go ahead and merge away!

16

This is now merged! If any plugin authors are struggling here, let us know in a new dedicated topic!

Great work Kris!!!