detect-secrets-hook read file list from a file, to allow use of exit code

[gpflaum]

• I'm submitting a ...

  • bug report
  • feature request

• What is the current behavior?
  detect-secrets-hook gets a list of files as command line arguments.

• What is the desired behavior?
  detect-secrets-hook optionally reads a list of files from a file.

• What is the motivation / use case for changing the behavior?
  The documentation suggest using xargs to construct and run the detect-secrets-hook command line. A problem with this approach is that the caller of xargs, such as a git pre-commit hook or build pipeline, gets the exit code from xargs, not detect-secrets-hook.
  
  I want to distinguish between detect-secrets-hook's exit code 1 (found a secret) and exit code 3 (no new secrets, but updated the baseline, e.g. from 1.4.0 to 1.5.0). In the latter case I don't want to block the commit or build pipeline. But xargs returns the same exit code, 123, in both cases.
  
  If detect-secrets-hook could read a list of files from a file, we could call detect-secrets-hook directly, without xargs, and receive the detect-secrets-hook exit code. This would also help when there are many files to scan: If the command line constructed by xargs is long, it may call detect-secrets-hook multiple times. Using a file as input, detect-secrets-hook could run just once.
  
  Using xargs can also cause problems when many files are being scanned: If the detect-secrets-hook command line would be longer than xargs' limit (128 Kb characters), xargs will run detect-secrets-hook multiple times with a shorter command line. If the first run of detect-secrets-hook modifies the baseline, any additional runs will fail with "Your baseline file (.secrets.baseline) is unstaged."
  
  Because filenames may contain newlines, there should also be an option like xarg's --null (-0) for reading null-terminated strings from the file.

• Please tell us about your environment:

  • detect-secrets Version: 1.5.0
  • Python Version: 3.11.2

[gpflaum]

Upgrading from detect-secrets 1.4 to 1.5 is causing problems for us because detect-secrets-hook 1.5 updates the baseline file even if no new secrets are found. It returns exit code 3 in this case, causing failures in our build pipelines. I'd like to ignore that case, but it's difficult to get the exit code when using xargs.

[gpflaum]

Updated the description with an additional problem that can happen when using xargs and scanning very many files.