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Xdebug Update: March 2020

Another month, another monthly update where I explain what happened with Xdebug development in this past month. It will be published on the first Tuesday after the 5th of each month. Patreon supporters will get it earlier, on the first of each month. You can become a patron here to support my work on Xdebug. If you are leading a team or company, then it is also possible to support Xdebug through a subscription.

In March, I worked on Xdebug for about 75 hours, on the following things:

Xdebug 2.9.3 and 2.9.4

The last month saw two releases. In Xdebug 2.9.3 I fixed an issue with breakpoint resolving. In files with a class that inherits from another class, the line start/end information from the inherited methods were incorrectly added to the lines map for the file with the extending class. This caused Xdebug to stop at confusing lines in some cases.

Xdebug overloads PHP's internal error handler. As the hooks in the PHP engine aren't great, Xdebug reimplements most of this. This code is liable for getting out of sync with how PHP itself handles errors. In Xdebug 2.9.3 I fixed such an issue, where a behavioural change in PHP 7.2 was not propagated to Xdebug's reimplementation of the error handler.

Through a discussion with other PHP contributors I found out that Xdebug's way of handling the overriding of opcodes (PHP Engine's "instructions") was not optimal. Other extensions also overload opcodes, such as Nikita's scalar objects, or Xinchen's taint. When Xdebug and one of these other opcode-overloading extensions are loaded at the same time, none of them would check whether they were also overloaded by another extension. In Xdebug 2.9.3 I fixed that, and this is now also resolved in taint, although the issue for scalar objects is still open.

Unfortunately this fixed introduced a crash for thread safe builds of PHP. I quickly released Xdebug 2.9.4 to rectify this problem after a number of reports.

Last month I mentioned that I merged a patch for Asynchronous Debugging Support into Xdebug's master branch (which will become Xdebug 3.0). While doing some more work on this, in particularly towards making it less of a performance impact, I found a bug that was present in Xdebug for a long time: When an IDE uses the detach command, Xdebug would disable the remote debugger for the entire life time of the PHP process in use. This potentially explains lots of weird situations where debugger suddenly stopped working. This bug is also fixed in Xdebug 2.9.4.

Xdebug 3

I've been continuing to work on little improvements for Xdebug 3, such as adding Units to profiler output's categories. This is a feature that was thought up when I did an Xdebug workshop last year at CHECK24. I expect to start with the refactoring of php.ini settings in April, as I am Staying Safe at Home, and pretty much have nothing else going on.

I've also continue to improve the dbgpClient and dbgpProxy tools, and made further progress on Xdebug Cloud.

Business Supporter Scheme and Funding

In March, no new supporters signed up.

If you, or your company, would also like to support Xdebug, head over to the support page!

Besides business support, I also maintain a Patreon page and a profile on GitHub sponsors.


The PHP Internals News continues its second season. In this weekly podcast, I discuss in 15-30 minutes, proposed new features to the PHP language with fellow PHP internals developers. It is available on Spotify and iTunes, and through an RSS Feed.


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