feat(v2): add option to toggle sidebar category open by default

[jsjoeio]

This PR adds the ability to toggle sidebar categories open by default.

Changes

• update sidebar category to take collapsed prop
• add extra sidebars collapsed test
• only mutate item.collapsed if necessary
• update docs for SidebarItemCategory

Motivation

Fixes #2354

Have you read the Contributing Guidelines on pull requests?

Yes.

Test Plan

I wrote extensive notes on the issue: #2354

Here's how I tested my changes:

1. Built project: yarn build
2. Published to verdaccio locally: yarn lerna publish --registry http://localhost:4873 --no-git-tag-version
3. Created a new website:

# set the registry to verdaccio
npm set registry http://localhost:4873/
# install @docusaurus/init globally
npm i -g @docusaurus/init
# run the binary from the location directly
/Users/jprevite/.nvm/versions/node/v10.15.1/lib/node_modules/@docusaurus/init/bin/index.js init test-joe

4. Modified the sidebars.js file:

module.exports = {
  someSidebar: 
     [
      {
        "type": "category",
        "label": "Introduction",
        "items": ["doc1"],
        "collapsed": true
      },
      {
        "type": "category",
        "label": "Powering MDX",
        "items": ["doc2"],
        "collapsed": false
      }
    ]
  }

5. Tested if changes worked (and they did 🎉). You can tell because "Powering MDX" is not collapsed (because it's set to false in the sidebars.js file.
   

Screenshots

Here are a few other screenshots of it in action:

Before

This is what happens before I made any changes. (note: I load the page, "Powering MDX" is collapsed).

After

I made the change and now it loads and is expanded (not collapsed) like I want!

And, if I'm on the "Powering MDX", it should be expanded (because it's the current page), which still works as expected.

Related PRs

(If this PR adds or changes functionality, please take some time to update the docs at https://github.com/facebook/docusaurus, and link to your PR here.)

[docusaurus-bot]

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[jsjoeio]

The following tests are failing:

• docsVersion
  • first time versioning
  • not the first time versioning
• loadSidebars
  • sidebars with known sidebar item type
  • sidebars shortand and longform lead to exact same sidebar
  • sidebars link
• versioned website
  • content

Any guidance on how to fix these would be awesome!

[jsjoeio]

Additional suggestions (out of the scope of this work):

• we should link to the local-third-party-project-testing.md in the CONTRIBUTING.md
• the swizzle section of the docs should have an example:

yarn swizzle @docusaurus/theme-classic DocSidebar

[lex111]

@jsjoeio if I understand correctly, you just need to update snapshots, run yarn test -u.

[jsjoeio]

if I understand correctly, you just need to update snapshots, run yarn test -u.

That worked for the snapshot tests! Now I just have to fix the actual test that I broke 😂 Thank you @lex111 🎉

[yangshun]

Thank you Joe!

[yangshun]

@jsjoeio We should also update the docs to tell people about this cool new feature :)

[jsjoeio]

We should also update the docs to tell people about this cool new feature :)

@yangshun Yes! Agreed :) I updated the example here in this PR.

I'll open a separate PR and add a short paragraph to that section of the docs!

[yangshun]

@jsjoeio seems like there was a bug, found by @lex111. We have to resubmit this PR.

[jsjoeio]

@yangshun Oh no! Okay. Do you want me to do that? (i.e. open a new PR with this work?)

[jsjoeio]

@yangshun actually, I'd like to propose moving this conversation to #2354 so it's easier to keep track of