Aggregate and deduplicate your deprecation warnings in Rails

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We know we all stay on the cutting edge of Rails; no one, and I mean no one out there is making a 4.2 -> 5.2 upgrade because Rails 4.2 is no longer supported.

You, dear reader, have just suddenly found an interest in resolving deprecation warnings, and as one jumps a few Rails versions in short order, finding and resolving them systematically will save you a lot of time.

Sure, you could run tail -f log/test.log | grep "DEPRECATION WARNING", but that’s not systematic. If the same line of code gets called 50 times, and prints a deprecation warning each time, that generates a lot of noise, not much signal.

This does no one any good:

Here’s what I settled on:

1. In one terminal window, run tail -f log/test.log | grep "DEPRECATION WARNING" >> deprecation_warnings.txt
2. In another terminal window, run all your tests. rails test or whatever.

If you take a look at deprecation_warnings.txt after all your tests run, you’ll see plenty of deprecation warnings. Maybe even a few hundred lines of them.

Daunting, eh?

Lets make that less daunting:

We’re going to remove all duplicates from that list, so the final output will show just the unique deprecation warnings.

Run:

sort deprecation_warnings.txt | uniq -c > unique_deprecation_warnings.txt

You have to sort the file and pipe it into uniq. The -c flag prints the number of occurrences of each line. This might help you figure out where to get started in resolving the dependencies.

Now, the contents of unique_deprecation_warnings.txt is one line per deprecation warning that popped up when running your tests (or, you could do this with log/development.log and exercising/running the app locally) and you can be a bit more systematic in resolving these deprecation warnings.

I originally got 300 lines of deprecation warnings; once I sorted and deduplicated that list, I was down to 18. Much more manageable!

This is much more usable!

Since the deprecation warnings include the specific line of code that generates the warning, this list now functions as a checklist of what I need to resolve in the app.