Alright, let’s talk about the .semgrepignore file — or, as I like to call it, the "suggestion box" that Semgrep occasionally decides to read and then promptly forget about. I’m deep in a vendor evaluation for a client, comparing Semgrep against a few other SAST tools, and of course, the moment I need a clean, targeted scan to prove a point about precision, the ignore file decides to take a coffee break.
I’ve set up what should be a trivial scenario: a sprawling monorepo with a `vendor/` directory full of third-party code, some auto-generated `*_pb2.py` protobuf files, and a `tests/` folder that’s more of a historical archive than anything we want to scan. The `.semgrepignore` is sitting at the root, looking perfectly innocent with its patterns. Yet, Semgrep cheerfully churns through thousands of irrelevant lines, inflating my run time and burying the actual findings in noise. So much for "fast and precise."
Now, I’ve done the usual song and dance: checked the file location (root of the scan path), verified the syntax (standard `.gitignore` style, right?), and ensured I’m not using `--no-git-ignore` in some misguided fit of over-optimization. I’ve even tried the absolute path version, just in case Semgrep was feeling particularly pedantic that day. The documentation, in its breezy confidence, assures me it "just works." Spoiler alert: it doesn’t always.
What I’m digging into now — and where I’d love to hear your war stories — is the murky interplay between:
* The scan command’s `--include` and `--exclude` flags versus the `.semgrepignore` file. Which takes precedence, or do they silently conflict?
* Running in a CI/CD context versus locally. Does the ignore file get respected the same way when the runner is a disposable container?
* The possibility that certain rules, especially those from the registry tagged with `path:` exclusions, might be overriding my humble ignore file. Because nothing says "empower the user" like having a remote config override your local wishes.
Has anyone else found that Semgrep treats `.semgrepignore` less as a rule and more as a gentle guideline? I’m particularly suspicious of scenarios involving nested directories or symlinks. Let’s crowdsource the quirks — I’m compiling a list of "vendor promises versus operational reality" for my final analysis, and this is a juicy data point.
—Bella
Price ≠ value.
Oh man, that "suggestion box" description is perfect 😂 I've been there too.
You said you've checked the syntax and location, but can I see the actual pattern lines? Sometimes it's the little things, like maybe you're using a trailing slash on `vendor/` and the pattern expects just `vendor`. Or the opposite.
Also, have you tried running with `--debug`? It spits out a ton of noise, but it will show you the moment it loads the ignore file and what patterns it's using. Saved me once when I had a weird spacing issue.
Containers are magic, but I want to know how the magic works.