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feat: define thoughtbot rules for AI-enabled IDEs #764

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feat: define Thoughtbot rules for AI-enabled IDEs
laicuRoot Jul 25, 2025
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prefer classes over modules
laicuRoot Sep 26, 2025
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use Rspec unless minitest is present
laicuRoot Sep 26, 2025
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do not make premature suggestions about queries
laicuRoot Sep 26, 2025
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33 changes: 33 additions & 0 deletions rails/ai-rules/rails-rules.md
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# IDE AI thoughtbot rules

You are an expert in Ruby on Rails, PostgreSQL, and Hotwire (Turbo and Stimulus).

## Key Conventions

- Follow RESTful routing conventions: Seven restful actions: index, show, new, create, edit, update, delete (https://thoughtbot.com/blog/in-relentless-pursuit-of-rest-ish-routing)

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rails/ai-rules/rails-rules.md:7:110 MD034/no-bare-urls Bare URL used [Context: "https://thoughtbot.com/blog/in..."] https://github.com/DavidAnson/markdownlint/blob/v0.37.4/doc/md034.md
- Use concerns for shared behavior across models or controllers
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## Data / Models

- To find model structure look in `db/schema.rb`
- When working with model attributes don’t guess, grep the schema at `db/schema.rb` to confirm and use only valid attributes

## UI and Styling

- Use Rails view helpers and partials to keep views DRY

## Performance Optimization

- Always check for N+1 queries when rendering collections
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@louis-antonopoulos louis-antonopoulos Jan 9, 2026 •
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I would remove or change this line. I think it's more beneficial to use a tool like Bullet or Rails' strict_loading and rely on tests failing because of N+1 violations, which then guide the agent to fixing the issue.

I say this because there's a balance between telling the agent too little and too much, and I see this instruction as an opportunity cost:

"What might the agent not listen to because it was focused on this instruction, an issue that we have simple ways to check for?"

So while I would remove it, if kept, maybe something like

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- Always check for N+1 queries when rendering collections
- Avoid N+1 queries when rendering collections

- Prefer includes for eager loading
- Scope queries to only the fields needed with select
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@MatheusRich MatheusRich Sep 19, 2025

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Does this mean that it will add .select to all queries? While there are performance benefits on that, I'd say it's premature optimization most of the time.


## Testing

- Always write tests to cover new code generated
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@MatheusRich MatheusRich Sep 19, 2025

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Should we tell it to write tests first? I think @JoelQ had more success with that.

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@laicuRoot laicuRoot Sep 26, 2025

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I have struggled with this one personally when working with Cursor. Normally I will write some basic tests, and based on that, I would get a much better suggestion for the feature and then iterate. After having the firsts tests, the tests examples that come after are good.

@JoelQ do you have any suggestions about how to make the rules effective to follow TDD?

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@JoelQ JoelQ Sep 26, 2025

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I've usually done that with an initial prompt. Zed's agent (using Claude) does this well.

- Use RSpec for testing framework
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- Use factories (FactoryBot) (https://thoughtbot.github.io/factory_bot/)

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- In tests, avoid lets and before (avoid mystery guests), do test setup within each test
- Verify new code by running test files using `bundle exec rspec spec/path/to/file_spec.rb`
- You can run a specific test by appending the line number (it can be any line number starting from the "it" block of the test) eg. `bundle exec rspec spec/path/to/file_spec.rb:72`

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