Recently I've been working in the EOS update. The change is really big because EOS has some modifications over the upstream code so there are a lot of commits applied after the last stable upstream commit.
EOS 3.5 was based on gnome 3.26 and we are updating to use the gnome 3.32 so all the downstream changes done since the last release should be rebased on top of the new code and during this process we refactor the code and commits using new tools and remove what's now in gnome upstream.
I've been working in the Hack computer custom functionality that's on top of the EOS desktop and basically I've been rebasing the code in the shell to do the Flip to Hack, the Clubhouse, a side component and notification override to propse hack quests and the wobbly windows effects.
Here comes the blindfolded debugging. I've a development system with a lot of changes and a functionality in the gnome shell that depends on different projects, applications and technologies.
I don't know the code a lot, because I'm not the one that wrote all of this, I'm working here since February, so I know a bit how things works, but I'm not the one who knows everything, there are a lot of rare cases that I don't know about.
I've found and fixes several bugs in different projects, that I don't know about a lot, during this process. How can I do that? If you are a developer that write code since a few years maybe you've experienced something similar, I'm calling this the blindfolded debugging technique:
Start to change code without knowing exactly what you're doing, but with a small feeling that maybe that line is the problem.
This technique is only for experienced programmers, as a kungfu master that put a blindfold in their eyes to fight against an opponent, the developer that will be brave enough to try this should have a lot of experience or he will fail.
You're an experienced developer, but you don't know the software that you're debugging. It doesn't matter. The same way that in a kungfu fight you don't know your opponent, but almost every fighter has two arms and two legs, so more or less you'll know that he'll try to punch you or kick you, you've a clue. As a programmer, every software has an structure, functions, loops...
No matters who wrote that or how old that code is, if you're an experienced programmer you'll feel the code and without knowing exactly why or how, you will be able to look at one line and says: Here you're little buggy friend.
Maybe I'm only trying to justify my lucky with a story to feel better and say that I'm not a dumb changing random lines to try to find a bug, but I'm sure that other developers has this feeling too, that feeling that guides you to the exact problem but that you're not able to rationalize.
I think that this is the experience, the expertise is your body and your inner brain doing the work meanwhile you don't need to think about it or know exactly what you are doing.