Markdown Live preview for Source Editor

What does this MR do?

Introduces the Live Preview functionality for the markdown extension of Source Editor. At the moment, the extension is only used when editing markdown files in a repository (single-file editor). Live Preview for WebIDE will be added as a separate MR.

Screenshots or Screencasts (strongly suggested)

How to setup and validate locally (strongly suggested)

1. Open a file in a project
2. Click "Edit" (not WebIDE or Gitpod)
3. You will get the regular instance of Source editor at this moment
4. While focused in the editor do one of the following:
   • right-click and select "Preview Markdown", or
   • press SHIFT + Command + P (Shift + Ctrl + P on Windows)
5. This will open the live preview panel to the right of the editor

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #280798 (closed)

changed milestone to %14.2

added Deliverable GitLab Free Source Editor Technical Writing auto updated devopscreate direction documentation frontend groupeditor [DEPRECATED] markdown quad-planningcomplete-action sectiondev tw-weight5 typefeature workflowin dev labels

assigned to @dmishunov

mentioned in commit 1861bab8

added 1 commit

• 1861bab8 - Markdown Live preview for Source Editor

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	1 Warning
	This merge request is quite big (522 lines changed), please consider splitting it into multiple merge requests.

Reviewer roulette

Changes that require review have been detected!

Please refer to the table below for assigning reviewers and maintainers suggested by Danger in the specified category:

Category	Reviewer	Maintainer
frontend	Thomas Randolph (@thomasrandolph) (UTC-6, 8 hours behind @dmishunov)	Paul Slaughter (@pslaughter) (UTC-5, 7 hours behind @dmishunov)

To spread load more evenly across eligible reviewers, Danger has picked a candidate for each review slot, based on their timezone. Feel free to override these selections if you think someone else would be better-suited or use the GitLab Review Workload Dashboard to find other available reviewers.

To read more on how to use the reviewer roulette, please take a look at the Engineering workflow and code review guidelines. Please consider assigning a reviewer or maintainer who is a domain expert in the area of the merge request.

Once you've decided who will review this merge request, assign them as a reviewer! Danger does not automatically notify them for you.

If needed, you can retry the danger-review job that generated this comment.

Generated by Danger

changed the description

mentioned in commit 4eedb482

added 1 commit

• 4eedb482 - Markdown Live preview for Source Editor

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mentioned in commit fd72a779

added 1 commit

• fd72a779 - Markdown Live preview for Source Editor

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@mlunoe could you please give this MR a technical review?

requested review from @mlunoe

Bundle size analysis [beta]

This compares changes in bundle size for entry points between the commits 192e2526 and 54febab7

Special assets

Entrypoint / Name	Size before	Size after	Diff	Diff in percent
average	3.09 MB	3.09 MB	-	0.0 %
mainChunk	1.85 MB	1.85 MB	-	0.0 %

---

Note: We do not have exact data for 192e2526. So we have used data from: 9453a015.
The target commit was too new, so we used the latest commit from master we have info on.
It might help to rerun the bundle-size-review job
This might mean that you have a few false positives in this report. If something unrelated to your code changes is reported, you can check this comparison in order to see if they caused this change.

Please look at the full report for more details

---

Read more about how this report works.

Generated by Danger

Allure report

allure-report-publisher generated test report for 54febab7!

review-qa-smoke: test report

requested review from @djadmin and removed review request for @mlunoe

UX (non-blocker): It looks like the scrollbar placement is not aligned with part of the screen, refer the screencast below. I don't think this will be any blocker for the MR, but feel free to take a UX suggestions on it if you'd like to.

mentioned in commit 94a80607

added 434 commits

• fd72a779...1e214a79 - 431 commits from branch master
• 94a80607 - Markdown Live preview for Source Editor
• f55dd51e - Minor refactoring of the spec
• c32c38df - Addressing the review

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mentioned in commit 2fffee26

added 119 commits

• c32c38df...32fdecd7 - 115 commits from branch master
• 2fffee26 - Markdown Live preview for Source Editor
• aba59df1 - Minor refactoring of the spec
• 7c9516fb - Addressing the review
• bdef5242 - Refactoring the markdown extension

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added 1 commit

• b2853826 - Refactoring the markdown extension

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added 1 commit

• 72cab205 - Refactoring the markdown extension

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added 1 commit

• 866b7a96 - Refactoring the markdown extension

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requested review from @kushalpandya

@dmishunov Thanks for adding this feature! It would save me from switching tabs! I've left a couple of initial findings, but will also try it out locally.

removed review request for @kushalpandya

added 1 commit

• 54febab7 - Switched to mocked axios adapter

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requested review from @kushalpandya and removed review request for @djadmin

resolved all threads

approved this merge request

@kushalpandya, thanks for approving this merge request.

This is the first time the merge request is approved. To ensure full test coverage, a new pipeline has been started.

For more info, please refer to the following links:

• rspec minimal jobs
• merging a merge request.

enabled an automatic merge when the pipeline for 920d2da6 succeeds

merged

mentioned in commit e7135c97

added workflowstaging label and removed workflowin dev label

added workflowcanary label and removed workflowstaging label