Tombstones, Vampires & Discovering Dead Code

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Presented by Chris Gmyr @cmgmyr

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What are we going to learn? → What is technical debt? → Efficiently find dead code → Remove code with confidence

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What is technical debt? The implied cost of additional rework caused by choosing an easy solution now instead of using a better approach. If technical debt is not repaid, it accumulates 'interest', making it harder to implement changes later on...

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What is technical debt? ...Technical debt is not necessarily a bad thing, and sometimes is required to move projects forward. → https://en.wikipedia.org/wiki/Technical_debt

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What does technical debt look like?

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Crowdpac Codebase → Laravel 4.2 → ~300 Classes → ~50,000 Logical lines of code → 667.13 Average system complexity score → (excludes: migrations, tests, views)

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How do we start paying back our technical debt?

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Pay back technical debt by → remove commented out blocks of code → improve your test suite (or start one) → refactor code you're currently working on → removing dead code

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What is "dead code"? → not referenced → referenced, not executed → no longer provides business value

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Great, let's remove some code!

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PHP "gotchas" → Dynamic language → Magic methods → Easy to write "bad" code

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Variable Functions function foo() { echo "In foo()
\n"; } $func = 'foo'; $func(); We can't search for references of foo()

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Variable Functions function displayName($name) { echo $name; } $func = 'display' . ucwords($_GET['property']); $func($_GET['property_value']); How are we easily going to search for displayName() usages?

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Magic Methods __construct(), __destruct(), __call(), __callStatic(), __get(), __set(), __isset(), __unset(), __sleep(), __wakeup(), __toString(), __invoke(), __set_state(), __clone() and __debugInfo() http://php.net/manual/en/language.oop5.magic.php

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Magic Methods class User { public function __toString() { return $this->fullName(); } } echo new User('Chris Gmyr'); echo new User(['full_name' => 'Chris Gmyr']); $person = new User([...]); // User::make([...]); echo $person;

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Framework "Magic" class User { public function setPasswordAttribute($value) { $this->attributes['password'] = Hash::make($value); } public function getPasswordAttribute($value) { return 'HIDDEN'; } }

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Framework "Magic" User::create([ 'password' => $_POST['password'] // setPasswordAttribute() ]); $user->password = $_POST['password']; // setPasswordAttribute() echo $user->password; // getPasswordAttribute()

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Framework "Magic" class Post { public function scopePopular($query) { return $query->where('votes', '>', 100); } } $posts = Post::popular()->get(); // scopePopular()

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Searching for usages is inefﬁcient and error-prone

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Let's try this again...

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Using tombstones to ﬁnd dead code

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What is a tombstone? A marker (function) placed inside code that is assumed dead. When a tombstone is executed, tracking information is written to a log. public function reallyOldMethod() { tombstone('2017-10-31', 'cmgmyr'); //... }

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What is a vampire? Suspected dead code, marked with a tombstone, that is alive echo $user->fullName(); class User { public function fullName() // vampire! { tombstone('2017-10-31', 'cmgmyr'); // remove this return $this->first_name . ' ' . $this->last_name; } }

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PHP Implementation https://github.com/scheb/tombstone function tombstone($date, $author, $label = null) { try { $trace = TraceProvider::getTraceHere(); $streamHandler = new StreamHandler(dirname(__DIR__)."/logs/tombstones.log"); GraveyardProvider::getGraveyard()->addHandler($streamHandler); GraveyardProvider::getGraveyard()->tombstone($date, $author, $label, $trace); } catch (\Exception $e) { // } }

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PHP Implementation https://github.com/scheb/tombstone-analyzer

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Other Tombstone Implementations JavaScript https://blog.bugsnag.com/javascript-refactoring-with- bugsnag-and-tombstones/ Perl http://devblog.nestoria.com/post/115930183873/ tombstones-for-dead-code

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Let's set some tombstones!

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class Post { public function publishToMySpace() { tombstone('2017-10-31', 'cmgmyr'); //... } }

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class User { public function canPublishPost() { if ($this->isAwesome()) { if($this->type == 'zombie') { tombstone('2017-10-31', 'cmgmyr'); //... } //... } //... } }

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Add tombstones to suspected dead code

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...or ALL code...

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...and wait...

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Check the logs 2017-11-01 09:00:00 Vampire detected from tombstone('2017-10-31', 'cmgmyr') in User.php on line XXX in canPublishPost() ... 2017-11-02 09:00:00 Vampire detected from tombstone('2017-10-31', 'cmgmyr') in User.php on line XXX in canPublishPost() ... 2017-11-03 09:00:00 Vampire detected from tombstone('2017-10-31', 'cmgmyr') in User.php on line XXX in canPublishPost() ...

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class User { public function canPublishPost() { if ($this->isAwesome()) { if($this->type == 'zombie') { tombstone('2017-10-31', 'cmgmyr'); //... } //... } //... } }

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class Post { public function publishToMySpace() { tombstone('2017-10-31', 'cmgmyr'); //... } }

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class TombstoneWorkflow { public function __construct() { $this->makePlan(); $this->cleanCode(); } public function cleanCode() { $this->setTombstones(); while($this->codebaseHasVampires()) { $this->checkLogs(); $this->removeVampires(); } $this->reviewRemainingTombstones(); $this->removeDeadCode(); } }

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Crowdpac 2,400 initial tombstones (class methods) -750 locally -925 staging/production ~700 Remaining (30%)

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Who should utilize tombstones? → legacy code → complex domain → inherited codebase → upgrading a codebase

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So, why tombstones? → Low impact solution → Use with dynamic languages → High conﬁdence in removing code