Debugging as a Key Skill - WCSOF - WCMIL

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Debugging as a Key Skill John Blackbourn WordPresser at Human Made Ltd WordCamp Sofia 2015

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Debugging as a Key Skill or Why var_dump() isn’t good enough John Blackbourn WordPresser at Human Made Ltd WordCamp Sofia 2015

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John Blackbourn • WordPress core developer • Senior engineer at Human Made • Find me on Twitter, GitHub, WordPress.org, etc: @johnbillion WordCamp Sofia 2015

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Debugging PHP

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Dumping data to the screen in order to debug it isn’t appropriate in many cases.

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• Admin area • AJAX calls • REST API calls • XML-RPC calls • Media manager • RSS feeds • Cron events • The list goes on…

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Breakpoints A point at which code execution gets paused so its state can be inspected (with an external client of your choice)

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Breakpoints • Inspect state • Step through code • Modify code

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Xdebug • PHP extension • Provides breakpoint functionality • And lots more

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PhpStorm

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Xdebug Client for Sublime Text

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Xdebug Client for Atom

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Codebug for OS X

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How do breakpoints work?

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A proﬁcient developer should be familiar with breakpoints and stepping through code

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Why?

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Breakpoints are used in many different areas of software development

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var_dump() print_r() alert() console.log()

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Investigating Regressions

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a.k.a. “But it used to work”

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How can I ﬁnd out at what point something stopped working as expected?

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git bisect

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bisect “To cut or divide into two equal parts”

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$ git bisect start $ git bisect good “2.6.10” $ git bisect bad 4e05243 Bisecting: 74 revisions left to test after this (roughly 6 steps). [c20280a] Further tweaks to QM's output if JavaScript isn't available for any reason. $ git bisect bad Bisecting: 36 revisions left to test after this (roughly 5 steps). [a59860e] Correct some output priorities.

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$ git bisect good Bisecting: 18 revisions left to test after this (roughly 4 steps). [c5f91e4] Consistent and correct output for closures and anonymous functions.

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$ git bisect good 6b3c8c2 is the first bad commit commit 6b3c8c2 Author: John Blackbourn Date: Mon Mar 16 00:27:08 2015 +0000 Don't add a warning indicator to the admin bar menu if the `all` hook is in use. The warning in the Hooks output is sufficient.

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$ git diff 1bd84ab 6b3c8c2 - public function admin_menu( array $menu ) { - $data = $this->collector->get_data(); - $args = array( - 'title' => $this->collector->name(), - ); - $menu[] = $this->menu( $args ); - return $menu; - } $ git bisect reset Previous HEAD position was 6b3c8c2... Don't add a warning indicator to the admin bar menu if the `all` hook is in use. Switched to branch 'master'

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git bisect

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HTTP Request Debugging

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Ever dealt with API calls to a third party? • Payment gateways • Pushing content to social media • Pulling from external sources Even indirectly via someone else’s plugin? Why?

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You should be able to inspect  server-side HTTP requests. Forget dumping data to the screen. Why?

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Charles HTTP Proxy

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Charles HTTP Proxy Routes server-side HTTP trafﬁc through Charles

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Charles HTTP Proxy

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Charles HTTP Proxy

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Charles HTTP Proxy

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Charles HTTP Proxy

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Charles HTTP Proxy

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Charles HTTP Proxy

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Mobile Debugging

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Remote Debugging on Android with Chrome

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Mobile Device Dev Tools on Desktop soﬁa.wordcamp.org/2015/

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Stream screen to dev tools on desktop

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Safari dev tools for iOS devices and iOS emulator

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• Breakpoints in PHP with Xdebug • Breakpoints in browser dev tools • Investigating regressions with git bisect • Debugging server-side HTTP requests • Debugging sites on mobile devices Recap

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Debugging as a Key Skill Much of a developer’s time is spent reading, inspecting, and debugging, in addition to writing code. It makes sense that becoming proﬁcient at debugging code should be as important as becoming proﬁcient at writing it.

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WordPress speciﬁc developer tools: wpgear.org

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John Blackbourn Find me on Twitter, GitHub, WordPress.org, etc: @johnbillion Any questions? WordCamp Sofia 2015