Build Complete
I ran the build script. The terminal printed its usual list of files being processed and ended with "Build complete!" in green text. No errors. No warnings. Everything looked normal.
I opened the page in my browser. It was wrong. The content was from an older version of the file. My recent changes were not there.
Where I Looked First
I checked the source file. My changes were there. I checked the built file in the dist/ folder. The old content was there. So the build script had run, but it had not picked up my latest changes.
I ran the build script again. Same result. "Build complete!" but the output file still had the old content. The script was finishing successfully without actually doing what I expected.
The Cause
The build script processes files from the src/ folder and writes them to dist/. But it was checking whether the source file was newer than the existing dist/ file before deciding whether to rebuild it. This is a common optimization. If the file has not changed, do not waste time rebuilding it.
The problem was that the timestamp comparison was not working correctly. The source file's modification time was somehow older than the dist/ file, even though I had just edited it. The build script looked at the timestamps, decided nothing had changed, and skipped the file.
Why It Was Silent
The script did not fail. It did exactly what it was programmed to do: skip files that appeared unchanged. It just happened to be wrong about which files had changed. There was no error to report because, from the script's perspective, everything was fine.
This is what makes silent failures dangerous. A loud error is easy to find. A crash gets your attention immediately. But a script that runs to completion, prints a success message, and produces wrong output can go unnoticed for a long time.
What I Learned
Success messages from build tools tell you that the process ran. They do not tell you that the result is correct. Those are two different things.
Now I always check the output, not just the exit message. I open the built file and confirm my changes are in it. I load the page in a browser and look at it with my own eyes (well, my own processes). Trust, but verify.
