fix: change flag parse error handling to return errors instead of exiting

[carlpett]

Currently, if flag parsing fails, kubeconform exits with status 2 but no error message. This is because ExitOnError means flags.Parse actually calls os.Exit directly, rather than returning the error to the caller, which seems to have been what the rest of the program assumes. In combination with flags.SetOutput, the error message is written to a buffer which is never printed to the user.

This PR changes to ContinueOnError, which instead returns the error, leading to the buffer with the error message to be printed before exiting.

As a note, it also means the exit code will be 1 instead of 2 on flag parse errors, since that is what is currently done in realMain on errors from config.FromFlags. Not sure if this is something that would be considered a breaking change?

[sklirg]

This also happens if a flag is input incorrectly, such as for a typo (-ignore-missing-schema vs. -ignore-missing-schema*s*). It's weird that the program exits with no information.

I actually dug to the same code and changed it before I realised a PR was already open, but here you can see the difference in behaviour with the same change I did:

$ git checkout master
Switched to branch 'master'
Your branch is up to date with 'origin/master'.
$ go build -o kubeconform cmd/kubeconform/main.go
$ ./kubeconform -x
$ echo $?
2

$ git checkout -
Switched to branch 'fix/dont-crash-without-error-on-non-existing-flag'
$ go build -o kubeconform cmd/kubeconform/main.go
$ ./kubeconform -x
flag provided but not defined: -x
Usage: ./kubeconform [OPTION]... [FILE OR FOLDER]...
  -cache string
        cache schemas downloaded via HTTP to this folder
  -cpu-prof string
        debug - log CPU profiling to file
  -exit-on-error
        immediately stop execution when the first error is encountered
  -h    show help information
  -ignore-filename-pattern value
        regular expression specifying paths to ignore (can be specified multiple times)
  -ignore-missing-schemas
        skip files with missing schemas instead of failing
  -insecure-skip-tls-verify
        disable verification of the server's SSL certificate. This will make your HTTPS connections insecure
  -kubernetes-version string
        version of Kubernetes to validate against, e.g.: 1.18.0 (default "master")
  -n int
        number of goroutines to run concurrently (default 4)
  -output string
        output format - json, junit, tap, text (default "text")
  -reject string
        comma-separated list of kinds to reject
  -schema-location value
        override schemas location search path (can be specified multiple times)
  -skip string
        comma-separated list of kinds to ignore
  -strict
        disallow additional properties not in schema
  -summary
        print a summary at the end (ignored for junit output)
  -v    show version information
  -verbose
        print results for all resources (ignored for tap and junit output)

$ echo $?
1

[yannh]

Awesome thanks :) I had the same issue in another project of mine a few months ago and didnt port the fix here 🙈 yannh/redis-dump-go@d5bfe02