What can you do to a legacy codebase that will hav

Question

As you work in a legacy codebase what will have the greatest impact over time that will improve the quality of the codebase?

• Remove unused code
• Remove duplicated code
• Add unit tests to improve test coverage where coverage is low
• Create consistent formatting across files
• Update 3rd party software
• Reduce warnings generated by static analysis tools (i.e.Findbugs)

The codebase has been written by many developers with varying levels of expertise over many years, with a lot of areas untested and some untestable without spending a significant time on writing tests.

Answer 1

Late to the party, but the following may be worth doing where a function/method is used or referenced often:

• Local variables often tend to be poorly named in legacy code (often owing to their scope expanding when a method is modified, and not being updated to reflect this). Renaming these in line with their actual purpose can help clarify legacy code.
• Even just laying out the method slightly differently can work wonders - for instance, putting all the clauses of an if on one line.
• There might be stale/confusing code comments there already. Remove them if they're not needed, or amend them if you absolutely have to. (Of course, I'm not advocating removal of useful comments, just those that are a hindrance.)

These might not have the massive headline impact you're looking for, but they are low risk, particularly if the code can't be unit tested.

Answer 2

I work with a legacy 1M LOC application written and modified by about 50 programmers.

* Remove unused code

Almost useless... just ignore it. You wont get a big Return On Investment (ROI) from that one.

* Remove duplicated code

Actually, when I fix something I always search for duplicate. If I found some I put a generic function or comment all code occurrence for duplication (sometime, the effort for putting a generic function doesn't worth it). The main idea, is that I hate doing the same action more than once. Another reason is because there's always someone (could be me) that forget to check for other occurrence...

* Add unit tests to improve test coverage where coverage is low

Automated unit tests is wonderful... but if you have a big backlog, the task itself is hard to promote unless you have stability issue. Go with the part you are working on and hope that in a few year you have decent coverage.

* Create consistent formatting across files

IMO the difference in formatting is part of the legacy. It give you an hint about who or when the code was written. This can gave you some clue about how to behave in that part of the code. Doing the job of reformatting, isn't fun and it doesn't give any value for your customer.

* Update 3rd party software

Do it only if there's new really nice feature's or the version you have is not supported by the new operating system.

* Reduce warnings generated by static analysis tools

It can worth it. Sometime warning can hide a potential bug.

Answer 3

• Read Michael Feather's book "Working effectively with Legacy Code"

This is a GREAT book.

If you don't like that answer, then the best advice I can give would be:

• First, stop making new legacy code[1]

[1]: Legacy code = code without unit tests and therefore an unknown

Changing legacy code without an automated test suite in place is dangerous and irresponsible. Without good unit test coverage, you can't possibly know what affect those changes will have. Feathers recommends a "stranglehold" approach where you isolate areas of code you need to change, write some basic tests to verify basic assumptions, make small changes backed by unit tests, and work out from there.

NOTE: I'm not saying you need to stop everything and spend weeks writing tests for everything. Quite the contrary, just test around the areas you need to test and work out from there.

Jimmy Bogard and Ray Houston did an interesting screen cast on a subject very similar to this: http://www.lostechies.com/blogs/jimmy_bogard/archive/2008/05/06/pablotv-eliminating-static-dependencies-screencast.aspx

Answer 4

I can relate to this question as I currently have in my lap one of 'those' old school codebase. Its not really legacy but its certainly not followed the trend of the years.

I'll tell you the things I would love to fix in it as they bug me every day:

• Document the input and output variables
• Refactor the variable names so they actually mean something other and some hungarian notation prefix followed by an acronym of three letters with some obscure meaning. CammelCase is the way to go.
• I'm scared to death of changing any code as it will affect hundreds of clients that use the software and someone WILL notice even the most obscure side effect. Any repeatable regression tests would be a blessing since there are zero now.

The rest is really peanuts. These are the main problems with a legacy codebase, they really eat up tons of time.

Answer 5

I would say just leave it alone for the most part. If it's not broken then don't fix it. If it is broken then go ahead and fix and improve the portion of the code that is broken and its immediately surrounding code. You can use the pain of the bug or sorely missing feature to justify the effort and expense of improving that part.

I would not recommend any wholesale kind of rewrite, refactor, reformat, or putting in of unit tests that is not guided by actual business or end-user need.

If you do get the opportunity to fix something, then do it right (the chance of doing it right the first time might have already passed, but since you are touching that part again might as well do it right time around) and this includes all the items you mentioned.

So in summary, there's no single or just a few things that you should do. You should do it all but in small portions and in an opportunistic manner.