The Hitchhiker's Guide to Servo Contributor

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The Hitchhiker’s Guide to Servo Contributor @_cybai, HERP, Inc. Rust.Tokyo

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whoami ● Haku ● @CYBAI ● @_cybai ● Software Engineer @ HERP, Inc. ● Contribute to Servo from Aug 2017 2

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● What is Servo? ● How to contribute? ● How to run tests? ● How Servo CI works? Agenda 3

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● What is Servo? ● How to contribute? ● How to run tests? ● How Servo CI works? Agenda 4

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● A modern, high-performance greenﬁeld browser engine designed for both application and embedded use ● Written in Rust ● Aim to achieve parallel and concurrency computing and layout ● Derived memory safety and security from Rust What is Servo? 5

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What is Servo? (Cont.) ● Two successful components have been migrated into Firefox, e.g. Stylo and WebRender 6

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Demo 7

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● What is Servo? ● How to contribute? ● How to run tests? ● How Servo CI works? Agenda 8

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Workﬂow 9 Find issue Implementation Test related WPT locally Send / Update PR Review PR merged Run CI passed with r+ Check Failures : Sucess : Failure

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How to get involved? ● Check E-* labels ○ E stands for Effort here. ○ E-easy and E-less easy are good for new contributors. ○ E-candidate-for-mentoring means it might be an easy issue because members didn’t check it carefully. But, they will mentor you to ﬁnish the issue. ○ E-hard means challenging tasks. 10 Ref: Tag label names and definitions

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How to get involved? (Cont.) ● Check the Servo starter page. ● Find any Web API you’re interested in and it’s missing or implemented incorrectly in Servo! 11

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12 The first issue I fixed

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13 From WHATWG DOM spec

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15 But, how can I conﬁrm my implementation is correct?

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● What is Servo? ● How to contribute? ● How to run tests? ● How Servo CI works? Agenda 16

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WPT ● In Software Engineering, writing tests to verify our business logic is indispensable. ● So do the web platforms! ● Here comes the Web Platform Tests a.k.a wpt. 17

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“The web-platform-tests project is a W3C-coordinated attempt to build a cross-browser test suite for the Web-platform stack.” -- web-platform-tests.org What is wpt? 18

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Brief introduction to WPT metadata 19

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How to run tests with Servo CI? 20 Ask @bors-servo to trigger “try” tests

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How to run tests with Servo CI? (Cont.) 21 CI tests triggered by try will report tests result when all tests passed instead of merging PR

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How to run tests with Servo CI? (Cont.) 22 But wait! Let’s see what @jdm said!

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How to run tests with Servo CI? (Cont.) 23

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WPT Synchronization 24 Sync new / fixed tests Contribute new / fixed tests

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25 After upstream tests synced and try again, finally got unexpected PASS!

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26 Approved by @jdm after the tests marked as PASS

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But wait! Why not just merge the PR? and what exactly is @bors-servo and r+? 27

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● What is Servo? ● How to contribute? ● How to run tests? ● How Servo CI works? Agenda 28

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Homu: The Not Rocket Science™ bors is ﬁrst introduced by Graydon Hoare who is Rust’s original creator and mainly applied Ben Elliston’s “not rocket science” rule to the bot: 29 The Not Rocket Science Rule Of Software Engineering: automatically maintain a repository of code that always passes all the tests -- Ben Elliston

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Homu: The Not Rocket Science™ 30 Rename fn foo → fn bar ✅ CI Pass Call fn foo in somewhere ✅ CI Pass ☠ Function foo doesn’t exist ❌ Broken master branch A B

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Homu: The Not Rocket Science™ 31 Screenshot from Homu Queue

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32 @bors-servo with r+ merged PR after CI passed

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Recap 33

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Recap 34 Write spec compliant tests Implement existing / new spec Contribute new / fixed tests

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Recap 35 Add / fix tests while changed Contribute spec bugfix or new feature Sync new / fixed tests

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References ● Experience Report: Developing the Servo Web Browser Engine using Rust ● technicalities: "not rocket science" (the story of monotone and bors) ● Rust infrastructure can be your infrastructure ● Servo: Designing and Implementing a Parallel Browser ● Servo and YOU: A beginner's guide ● Inside a super fast CSS engine: Quantum CSS (aka Stylo) ● The whole web at maximum FPS: How WebRender gets rid of jank 36