Logcheck: Separate correct usage and migration tests

[umangachapagain]

What this PR does / why we need it:

logcheck: add flag for migration test

Migration test is done by explicitly passing -migration flag to
logcheck. It runs correctness test but reports an error when
unstructured logging function is used in a migrated package.

Correctness test is run by default to check for correct usage
of structured logging patterns. It reports an error if structured
logging function is used incorrectly. It does not report an error
when structured logging function is not used.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes kubernetes/kubernetes/issues/102439

Special notes for your reviewer:

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

Release note:

NONE

[umangachapagain]

/cc @serathius

[serathius]

Let's avoid adding more globals, could you move Analyser and flag registration to functions?
I know globals are simpler, but they create a bad pattern in code. Let me know if you need help with this.

[umangachapagain]

Discussion here: #247 (comment)

[serathius]

Please avoid using global variables.

[umangachapagain]

@serathius I tried finding a way to do this, but it's either really tricky or not possible.

For flags, I had to use global variable as I couldn't find a way to pass it into run() where it's actually used.

For Analyzer, I had to make it global so that anyone can access it from outside. In our case, unit tests can't access it if it's not global and fails.

If you have suggestions on how to do it, I can add those changes to the PR.

[serathius]

Yea, it's a little harder then I thought at the beginning.

Try this:

type config struct {
	allowUnstructured bool
}

func main() {
	singlechecker.Main(analyser())
}

func analyser() *analysis.Analyzer {
	c := config{}
	logcheckFlags     := flag.NewFlagSet("", flag.ExitOnError)
	logcheckFlags.BoolVar(&c.allowUnstructured, "allow-unstructured", c.allowUnstructured, `suppress error reports when unstructured logging pattern is used`)

	return &analysis.Analyzer{
		Name:  "logcheck",
		Doc:   "Tool to check use of unstructured logging patterns.",
		Run: func(pass *analysis.Pass) (interface{}, error) {
			return run(pass, &c)
		},
		Flags: *logcheckFlags,
	}
}

func run(pass *analysis.Pass, c *config) (interface{}, error) {

[umangachapagain]

This is neat. Made the changes.

[serathius]

/lgtm
/assign @dims

[serathius]

/assign @brancz

[dims]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dims, serathius, umangachapagain

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