Ensuring that a codebase is consistent in style is both hard and costly, yet it is extremely important for maintainability and to reduce technical debt. This problem is one of the many pain points we are currently tackling with source{d} Lookout, our brand new assisted code review framework. The purpose of source{d} Lookout is to bring assisted code review to anyone in an easy-to-setup, easy-to-use, easy-to-extend fashion. To achieve that, source{d} Lookout watches Github repos and triggers a set of analyzers when new code is sent for review or pushed.

1. 2/4/2019 Assisted Code Review with source{d} Lookout
http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 1/52
Assisted Code Review with
source{d} Lookout
Vadim Markovtsev
Machine Learning for
Large Scale Code Analysis

2. 2/4/2019 Assisted Code Review with source{d} Lookout
http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 2/52
Plan
Origins
What is Lookout?
SDK
From scratch: typo correction
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Origins

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 6/52

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 7/52

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 8/52

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 9/52

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 11/52
Many efforts
target boring
stuff

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 12/52
Boring means
automatable

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 13/52
Automatable
≠ unattended

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When to help?
While you type = IDE
While you check = CI
While you review = PR
Periodically, asynchronously = cron
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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 15/52
IDE
Instant feedback
Rich information
Rich UI
Instant feedback
Many different IDEs and languages
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–
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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 16/52
CI
Part of the workflow
More time to run
No UI
Must not be wrong
Longer feedback loop
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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 17/52
PR reviews
Part of the workflow
More time to run
UI
Should not be wrong
Longer feedback loop
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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 18/52
cron
Plenty of time to run
Outside of the workflow
No UI
Longest feedback loop
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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 19/52
Comparison
∈∈ workflow UI Feedback Rich info FP requirements
IDE ✓ ✓✓ instant ✓ low
CI ✓ ✗ minutes ✗ 0
PR ✓ ✓ minutes ✗ lowest
cron ✗ ✗ hours ✗ low

20. 2/4/2019 Assisted Code Review with source{d} Lookout
http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 20/52
When to help?
While you type = IDE
While you check = CI
While you review = PR ←
Periodically, asynchronously
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→
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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 21/52
Welcome to the Codacy Blog
Insights for software builders
Subscribe

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What is
Lookout?

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 23/52
Goals
Assisted code review platform
Tight git/GitHub integration
Analyzed language agnostic
Implementation language agnostic
Batteries included
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Architecture

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 25/52
Push event

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 26/52
Push event

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 27/52
Push event

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 28/52
Push event

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 29/52
Push event

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 30/52
Push event

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Push event

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 33/52
PR event

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 34/52
PR event

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 35/52
docs.sourced.tech/lookout

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SDK

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 38/52
src-d/lookout-sdk
Single source of gRPC definitions
Low-level API: Go, Python
Low-level examples
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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 39/52
src-d/lookout-sdk-ml
High-level Python API
Stateful analyzers
Integrated with source{d} ml ecosystem
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Rule of

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High-level API
class MyAnalyzer(Analyzer):
@classmethod
def train(cls, ...) -> AnalyzerModel:
# ...
def analyze(self, ...) -> [Comment]:
# do something with self.model
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Train
@with_uasts_and_contents
def train(cls,
ptr: ReferencePointer,
config: Dict[str, Any],
data_service: DataService,
files: Iterable[File]
) -> AnalyzerModel:
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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 43/52
Analyze
@with_changed_uasts_and_contents
def analyze(self,
ptr_from: ReferencePointer,
ptr_to: ReferencePointer,
data_service: DataService,
changes: Iterable[Change]
) -> [Comment]:
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Behind the scenes
gRPC servers and clients
Pooling and threading
Database of trained models
Caches
Logging
Metrics
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Hands on

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 46/52
Objective
class Packfile:
Review

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 47/52
Objective
def read_packfile(...):
# ...
class Packfile:
Review
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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 48/52
Objective
def read_packfile(...):
# ...
class Packfle:
Review
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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 49/52
Steps
Install lookout-sdk-ml and autocorrect
Write typos.py
Fork a repo, create a PR
Generate a new GitHub Personal Access Token
Run our analyzer
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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 50/52
Summary

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http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 51/52
Summary
source{d} decided to build products for assisted code review
Lookout is a great platform for assisted code review
Writing new analyzers is easy and fun
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52. 2/4/2019 Assisted Code Review with source{d} Lookout
http://vmarkovtsev.github.io/mloncode-meetup-2019-webinar/ 52/52
Thank you
 src-d/lookout
 src-d/lookout-sdk-ml
 blog.sourced.tech
 medium.com/sourcedtech
 go.sourced.tech/newsletter
 sourcedtech
 vadimlearning bit.ly/2H8U5ra