chore: add custom copilot instructions COMPASS-10013

[paula-stacho]

Description

Note: I've tested a basic react antipattern and the freeStorage tag, but mostly I think we'll just need to see how it performs on real PRs and keep adjusting for a good signal-to-noise ratio.

Checklist

• New tests and/or benchmarks are included
• Documentation is changed or added
• If this change updates the UI, screenshots/videos are added and a design review is requested
• If this change could impact the load on the MongoDB cluster, please describe the expected and worst case impact
• I have signed the MongoDB Contributor License Agreement (https://www.mongodb.com/legal/contributor-agreement)

Motivation and Context

• Bugfix
• New feature
• Dependency update
• Misc

Open Questions

Dependents

Types of changes

• Backport Needed
• Patch (non-breaking change which fixes an issue)
• Minor (non-breaking change which adds functionality)
• Major (fix or feature that would cause existing functionality to change)

[Copilot]

Pull request overview

This PR adds custom Copilot instructions for code reviews and includes test changes to validate the reviewer's detection capabilities.

• Adds a new .github/copilot-instructions.md file with guidelines for code reviews
• Introduces intentional anti-pattern code in diagram-editor.tsx to test Copilot's detection

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
.github/copilot-instructions.md	New file defining custom instructions for Copilot code reviews, covering performance, code quality, best practices, and MongoDB-specific guidelines
packages/compass-data-modeling/src/components/diagram-editor.tsx	Adds unused import and intentional React anti-pattern (direct state mutation in useEffect) for testing purposes

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💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

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💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

This code directly mutates the state object instead of using the setObj setter function. Direct state mutation bypasses React's state management and will not trigger re-renders. Replace obj.a = 'abc' with setObj({ a: 'abc' }). Additionally, the dependency array [obj] will cause an infinite loop since obj is recreated on every render. See React documentation on state updates.

Suggested change

	obj.a = 'abc';
	}, [obj]);
	setObj({ a: 'abc' });
	}, []);

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

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💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

The freeStorage: 1 option can have significant performance implications on large deployments as it requires scanning all storage metadata. Consider documenting this performance impact and evaluating if this metric is necessary for all use cases. See https://www.mongodb.com/docs/manual/reference/command/dbStats/#performance-considerations

[nbbeeken]

Does this only configure the review bot or will it also change the local copilot experience. I think my comment may only be relevant to the local exp, generally I think we all do use the modern practices but I've seen copilot output a healthy amount of legacy stuff, it would be nice to steer it away

[nbbeeken]

I guess I don't want to give it too much of an opinion but either here or above I would add a mention of using modern JS practices since its been trained on a lot of legacy stuff, like I see copilot not using for-of when it should etc.

[paula-stacho]

Great point!