[roflyear]

No, it isn't common. As an engineer you know it doesn't matter if you're shown some code (what are you going to do? memorize it?) and signing an NDA should be a thing anyway if they are concerned about secrets, so what's the worry?

But, if you have any real experience in the industry (rather than making up fake advice which sounds good on the surface) you'll know that few companies will show their code, because there is little to no benefit to them doing so.

[Zvez]

I can also argue that is is almost impossible to show code to you for very simple reason: showing couple of files won't make any difference for you anyway and you can't just transfer your codebase to a person. The only thing you can do is to sit candidate to a laptop with the codebase for couple of hours, but I doubt anyone will go that far.

[atraac]

I'd argue that this will absolutely help filter out abysmal codebases made by people who have no idea how to code. I've seen companies like that, I've seen people who don't know how to format code, how to write proper function names in English, hell, I've seen people making Polish comments in an English codebase with grammar errors in their native language. But I agree with other comments, doubt anyone would actually show you code during an interview due to legal reasons.