Dead code and one more way it could hit you back – by being loaded!
(Everyday Code – instead of keeping our knowledge in a README.md let’s share it with the internet)
We can all agree that dead code should be removed. What we sometimes fail to see is how much it could cost to leave dead code with our product. Today’s article is about an example of a “dead code” and how it hit us back 1.5 years after we stopped using it. It took us 3 hours to debug and find the root cause. The conclusion is that we should have done ‘git rm’ an year ago. We did not and the cost was 3 hours.
This is a real life example article from our code base and it is design to share experience with our team, but I hope the whole community could benefit.
What happened
1. Jenkins build failed
First time we saw it we identified that it is not something serious and it kept failing for a few days until we had time to address it in the next Sprint.
2. Teaspoon, Jasmine, Bundler, Rails Engines
In the project there was the production code in Rails.root along with a dummy test code for starting JavaScript specs in Rails.root/test/dummy/. We are using Teaspoon with Jasmine in a Rails engines. Rails engines tend to create a test/dummy folder in which you could put the code for a test app in which you want your JavaScript specs to be executed. The product code is loaded in the test app and specs are executed.
About 1.5 years ago I did some experiments with this test app and made a few configurations. The goal was to have the production code along with some test app code both loaded in the test environment. In this way Teaspoon and Jasmine would see both the production and the test app code as coming from “production”. I literally remembered what my idea was and what I was trying to achieve. At the end I decided not to use the test app code, but to have only the production code located in Rails.root be loaded in the test environment.
But I forgot to remove the test app code from test/dummy/app/assets/javascripts/
3. Teaspoon Error
The following error occurred. Here “IS” is a JavaScript namespace part of the production code.
jenkins@vpszap6s:~/jobs/is-core Build and Release/workspace/test/dummy$ xvfb-run -a bundle exec rake teaspoon --verbose
Starting the Teaspoon server...
Teaspoon running default suite at http://127.0.0.1:36051/teaspoon/default
ReferenceError: IS is not defined
4. The error and debugging process
Not sure what the error was exactly I tried to identify the difference between my machine and the server machine where the tests was failing. This server machine is called “elvis”.
- Bundler version – my version was 2.2.11 and the elvis version was 2.2.14. Tried with upgrade, but it did not resolve the issue.
- Chrome driver – since the tests were executed on chrome I saw the chrome driver versions were different. Mine was 86. elvis was with 89. Synced them, the error was still occurring.
- Rake version – rake versions were the same
- Ruby version – the same
- Teaspoon and Jasmine versions – the same
- The OS is the same
- I could not find any difference between my env and the elvis env.
Turns out the problem was in the loading order. elvis was loading test app code and then production code. My machine was loading production code and then test app code. I could not figure out why. The whole test app code was:
// test/dummy/app/assets/javascripts/ext/dummy/dummy.js
IS.Dummy = {};The error that was occurring was:
ReferenceError: IS is not defined5. Solution
I was curious to continue debugging to see why the two machines were loading the code in a different order, but at the end decided against it. Just removed the dead code in test/dummy/app/assets/javascripts/ext/dummy/dummy.js which I only thought as dead, but it turned out it was affecting our project.
6. Builds passing
Finally the builds were passing.
Conclusion
Dead code my not be that dead after all. It might be loaded even if not used and loading order could differ. Better be safe and remove dead code at all. If we need it that much, we have it in the GIT repo history.
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