how to silence warnings about ignored files in eslint

One workaround I know at the moment is --quiet option, which suppresses all warnings. Of course that doesn't make sense if you have "warn" rules in your config.

Another way not to show that warning is to use dir names: eslint src instead of globbing patterns: eslint src/*.

You can't and they don't plan on fixing it since they don't consider it a bug. So if you pass in a file that's being ignored them it will tell you it didn't process linting rules because it's ignored: https://github.com/eslint/eslint/issues/5623

We run pre-commit hooks to lint code before committing, so ended up needing to write some additional code to differentiate between actual Warnings and File ignored warnings and only fail linting if an actual warning or error is thrown.

Check if you're running eslint with an unquoted glob argument.
If so, put the glob in quotes.

eslint src/** ❌ Bad (no quotes = OS will expand into many args)

eslint "src/**" ✔️ Good (quotes = a single string argument)

Why?

If you call eslint using a cli glob pattern not in quotes, e.g. eslint src/**, that glob gets expanded into all matching files and passed to eslint as a gigantic list of cli arguments. e.g. eslint path/to/file/name.min.js src/foo.js src/bar.js src/manymore.js .....

So when eslint ignores a file due to your ignore pattern, yet that file was explicitly passed as a command line argument, eslint is warning us

eslint speaking:
"Um, I ignored /path/to/file/name.min.js because of an ignore pattern, but you explicitly passed it to me to lint, so this must not be what you wanted, right?"

But when you pass the glob in quotes, e.g. eslint "src/**", the glob is not expanded to many arguments; rather, it's just a single string argument, and eslint is the one who knows it's a glob but since it takes care of figuring out which files to match it can do so while respecting eslintignore. So there's nothing weird going on that eslint thinks it should warn you about.