bill and his blog


Unused Variables Broke Prod

Problem: This morning we broke production because (believe it or not) an unused variable went undetected.

Solution: Consume the variable in the relevant codepath.

Further AI: Treat unused variables as errors (which will block CI).

Warning/Disclaimer

I am not a C# programmer. I know close to nothing about C#. But at $WORK, one of our codebases is written in C#, so occasionally I interface with it.

Treating Unused Variables as Errors

C# uses .csproj files to configure projects. The following changes to our .csproj file WAI'd:

+    <!-- IDE0059: Remove unnecessary value assignment -->
+    <WarningsAsErrors>IDE0059</WarningsAsErrors>
+    <EnforceCodeStyleInBuild>true</EnforceCodeStyleInBuild>

However, supporting this turned out to be a ~1h adventure... Why was this unexpectedly difficult? As it turns out, there are the 3x promising compiler warnings that I had to discover/try:

Legend:

For CA and IDE prefixed warnings, EnforceCodeStyleInBuild must also be enabled.