103 lines
3.2 KiB
Markdown
103 lines
3.2 KiB
Markdown
# Gotchas
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The purpose of this guide is to document potential "gotchas" that contributors
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might encounter or should avoid during development of GitLab CE and EE.
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## Don't `describe` symbols
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Consider the following model spec:
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```ruby
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require 'rails_helper'
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describe User do
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describe :to_param do
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it 'converts the username to a param' do
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user = described_class.new(username: 'John Smith')
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expect(user.to_param).to eq 'john-smith'
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end
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end
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end
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```
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When run, this spec doesn't do what we might expect:
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```sh
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spec/models/user_spec.rb|6 error| Failure/Error: u = described_class.new NoMethodError: undefined method `new' for :to_param:Symbol
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```
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### Solution
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Except for the top-level `describe` block, always provide a String argument to
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`describe`.
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## Don't `rescue Exception`
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See ["Why is it bad style to `rescue Exception => e` in Ruby?"][Exception].
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_**Note:** This rule is [enforced automatically by
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Rubocop](https://gitlab.com/gitlab-org/gitlab-ce/blob/8-4-stable/.rubocop.yml#L911-914)._
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[Exception]: http://stackoverflow.com/q/10048173/223897
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## Don't use inline CoffeeScript in views
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Using the inline `:coffee` or `:coffeescript` Haml filters comes with a
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performance overhead.
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_**Note:** We've [removed these two filters](https://gitlab.com/gitlab-org/gitlab-ce/blob/8-5-stable/config/initializers/haml.rb)
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in an initializer._
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### Further reading
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- Pull Request: [Replace CoffeeScript block into JavaScript in Views](https://git.io/vztMu)
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- Stack Overflow: [Performance implications of using :coffescript filter inside HAML templates?](http://stackoverflow.com/a/17571242/223897)
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## ID-based CSS selectors need to be a bit more specific
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Normally, because HTML `id` attributes need to be unique to the page, it's
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perfectly fine to write some JavaScript like the following:
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```javascript
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$('#js-my-selector').hide();
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```
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However, there's a feature of GitLab's Markdown processing that [automatically
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adds anchors to header elements][ToC Processing], with the `id` attribute being
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automatically generated based on the content of the header.
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Unfortunately, this feature makes it possible for user-generated content to
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create a header element with the same `id` attribute we're using in our
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selector, potentially breaking the JavaScript behavior. A user could break the
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above example with the following Markdown:
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```markdown
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## JS My Selector
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```
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Which gets converted to the following HTML:
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```html
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<h2>
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<a id="js-my-selector" class="anchor" href="#js-my-selector" aria-hidden="true"></a>
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JS My Selector
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</h2>
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```
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[ToC Processing]: https://gitlab.com/gitlab-org/gitlab-ce/blob/8-4-stable/lib/banzai/filter/table_of_contents_filter.rb#L31-37
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### Solution
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The current recommended fix for this is to make our selectors slightly more
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specific:
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```javascript
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$('div#js-my-selector').hide();
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```
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### Further reading
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- Issue: [Merge request ToC anchor conflicts with tabs](https://gitlab.com/gitlab-org/gitlab-ce/issues/3908)
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- Merge Request: [Make tab target selectors less naive](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/2023)
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- Merge Request: [Make cross-project reference's clipboard target less naive](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/2024)
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