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You've just inherited a legacy C++ codebase, now what?

gaultier.github.io

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Re: You've just inherited a legacy C++ codebase, now what?

#251

Post by fransje26 »

skissane wrote: post #201
hyperman1 wrote: post #132

Earlier quoted context omitted.

If we're going to visit the circles of hell, let's do it properly: Step -1: Get it under source control and backed up. Step -2: Find out if the source code corresponds to the executable. Which of the 7 variants of the source code (if any). Step -3: Do dark rituals over a weekend with cdparanioa to scrape the source code from the bunch of scratched cd's found in someone's bottom drawer. Bonus point if said person died…

Question: Why does some of the product source code look like it is the output of a decompiler? Answer: Our office was in the WTC and was destroyed on 9/11. Luckily everyone got out alive, but then we discovered we had no off-site backups of the source code. In order to continue development, we had to retrieve the released binaries from our customers and decompile them to get back source code.

Oh.. Ouch, ouch, ouch. I feel for you. That must have been hell.

Re: You've just inherited a legacy C++ codebase, now what?

#252

Post by guappa »

skissane wrote: post #201
hyperman1 wrote: post #132

Earlier quoted context omitted.

If we're going to visit the circles of hell, let's do it properly: Step -1: Get it under source control and backed up. Step -2: Find out if the source code corresponds to the executable. Which of the 7 variants of the source code (if any). Step -3: Do dark rituals over a weekend with cdparanioa to scrape the source code from the bunch of scratched cd's found in someone's bottom drawer. Bonus point if said person died…

Question: Why does some of the product source code look like it is the output of a decompiler? Answer: Our office was in the WTC and was destroyed on 9/11. Luckily everyone got out alive, but then we discovered we had no off-site backups of the source code. In order to continue development, we had to retrieve the released binaries from our customers and decompile them to get back source code.

I see this as a case of: "see, allowing wfh would have saved you there."

Re: You've just inherited a legacy C++ codebase, now what?

#253

Post by fransje26 »

ta2234234242 wrote: post #204
hyperman1 wrote: post #132

Earlier quoted context omitted.

If we're going to visit the circles of hell, let's do it properly: Step -1: Get it under source control and backed up. Step -2: Find out if the source code corresponds to the executable. Which of the 7 variants of the source code (if any). Step -3: Do dark rituals over a weekend with cdparanioa to scrape the source code from the bunch of scratched cd's found in someone's bottom drawer. Bonus point if said person died…

Some people believe that if you read the C++ standard recreationally, it should be interpreted as a call for help, and intervention is required, putting the subject under 24/7 monitoring and physical restraints. /s Step -4: Get the version of windows and the compiler it was last known to compile with.

Step -3.5: Do the service pack and .net framework update dance, wave a dead chicken, and hopefully, by shear luck, install them in the correct order. If not, uninstall and goto -4;

Been there. Done that.

Re: You've just inherited a legacy C++ codebase, now what?

#254

Post by saagarjha »

Joel_Mckay wrote: post #21
Night_Thastus wrote: post #5

Earlier quoted context omitted.

IME, this only works if you can get regular help from them. A one-off won't help much at all.

I've always found discussing why former employees left a project incredibly enlightening. They will usually explain the reality behind the PR given they are no longer involved in the politics. Most importantly they will often tell you your best case future with a firm. Normally, employment agreements specifically restrict contact with former staff, or discussions of sensitive matters like compensation packages. C++ i…

Note that depending on your jurisdiction discussion of compensation may be a right protected by law.

Re: You've just inherited a legacy C++ codebase, now what?

#255

Post by fransje26 »

eschneider wrote: post #101
dataflow wrote: post #100

Earlier quoted context omitted.

Step 0: reproducible builds (like you said) Step 1: run all tests, mark all the flaky ones. Step 2: run all tests under sanitizers, mark all the ones that fail. Step 3: fix all the sanitizer failures. Step 4: (the other stuff you wrote)

Just a note on legacy tests: Step 0.5: understand the tests. They need to be examined to see if they've rotted or not. Tests passing/failing doesn't really mean code under test works or not. The tests might have been abandoned under previous management and don't accurately reflect how the code is _supposed_ to be working.

Look at mister fancy here, having tests in his legacy code base.

Re: You've just inherited a legacy C++ codebase, now what?

#256

Post by fransje26 »

skrebbel wrote: post #34
dralley wrote: post #31

Earlier quoted context omitted.

On the flip side, auto-formatting will trash your version history and impede analysis of "when and why was this line added".

You can ignore commits from git blame by adding them to a .gitattributes file. This is assuming Git of course, which is not a given at all for the average legacy c++ codebase.

Good to know. Thanks for the tip!

Re: You've just inherited a legacy C++ codebase, now what?

#257

Post by t43562 »

I think the very best thing one can do is reduce the amount of variation you have to support. The burden of change is thus vastly reduced and the number of possible avenues for improvement explodes.

We could have left customers with old operating systems on the older versions of the product. A lot of them never upgraded anyhow. We absolutely destroyed our productivity by not making this kind of decision. We also really hurt ourselves by supporting Windows - as soon as there are 2 or more completely different compilers things turn to **t. I'm not even sure we made much money from it.

Given the ability to use new tools (clang, gcc and others) that are only available on newer operating systems we could have done amazing things. All those address sanitizers etc would have been wonderful and I would like to have done some automated refactoring which I know clang has tools for.

Most of the problems were just with understanding the minds of the developers - they were doing something difficult and at a level of complexity that somewhat overmatched the problem most of the time but the complexity was there to handle the edge cases. I wanted to go around adding comments to the files and classes as I understood bits of it. I was working with one of the original developers who was of course not at all interested in anyone understanding it or making it clearer and this kind of effort tended to get shot down.

If you don't have good tests you're dead in the water. I have twice inherited python projects without tests at all and those were a complete nightmare until I added some. One was a long running build process in which unit tests were only partially helpful. Until I came up with a fake android source tree that could build in under a minute I was extremely handicapped. Once I had that everything started to get much better.

My favorite game ... is an open source C++ thing called warzone2100 - no tests. It's not easy to make changes with confidence. I imagine to myself that one day my contribution will be to add some. The problem is that I cannot imagine the current developers taking all that kindly to it. Some people get to competence in a codebase and leave it at that.

Re: You've just inherited a legacy C++ codebase, now what?

#258

Post by hobofan »

eschneider wrote: post #89

Some good advice here, and some more...controversial advice here. After inheriting quite a few giant C++ projects over the years, there are a few obvious big wins to start with: * Reproducible builds. The sanity you save will be your own. Pro-tip: wrap your build environment with docker (or your favorite packager) so that your tooling and dependencies become both explicit and reproducable. The sanity you save will be…

> wrap your build environment with docker (or your favorite packager) so that your tooling and dependencies become both explicit and reproducable

If you want explicitness and reproducibility please don't reach for Docker. Unless you take a lot of care, you will only get the most watered down version of reproducibility with Docker probably luring you into a false sense of security. E.g. pointing to mutable image tags without integrity hashes and invoking apt-get are things you'll find in most Dockerfiles out there and both leave open a huge surface area for things to go wrong and end up in slightly different states.

And while they are not that easy to pick up, solutions like Bazel and Nix will give you a lot better foundation to stand on.

Re: You've just inherited a legacy C++ codebase, now what?

#259

Post by fransje26 »

keepamovin wrote: post #3

It's funny. My first step would be 0. You reach out to the previous maintainers, visit them, buy them tea/beer and chat (eventually) about the codebase. Learned Wizards will teach you much. But I didn't see that anywhere. I think the rest of the suggestions (like get it running across platform, get tests passing) are useful stress tests likely to lead you to robustness and understanding however. But I'd def be going…

    > You reach out to the previous maintainers, visit them
I could have brought them flowers, and shared a moment of silence contemplating eternity. I don't know if it would significantly have helped understanding the code base though..

Re: You've just inherited a legacy C++ codebase, now what?

#260

Post by legacybob »

Every morning I wake up in my legacy bed, before taking breakfast using a legacy coffee cup. I then take a shower using - you guessed it - legacy shower taps (after all, I do live in a legacy building).

I then sit on my legacy chair to browse the Internet and read about brand new programming things (through a legacy monitor).

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