feat: exclude linters from severity-rules

[ealves-pt]

Currently when configuring severity-rules we lose the granularity provided by more advanced linters.

A good use case is revive that allows us to customize the severity per linter. Considering the configuration below all the revive issues will have info severity instead of the severity defined in revive.

I already brought this to discussion in the past, #1860, and I accepted the limitation. But now I'm trying to work on a more precise coding standard for my teams and having the ability to control this would be perfect.

linters:
  disable-all: true
  enable:
    - errcheck
    - gosimple
    - govet
    - ineffassign
    - staticcheck
    - unused
    - revive
 
linters-settings:
  revive:
    severity: error
    rules:
      - name: cognitive-complexity
        arguments: [15]
      - name: cyclomatic
        arguments: [12]
        severity: warning

severity:
  default-severity: info
  rules:
    - linters:
      - errcheck
      - gosimple
      - govet
      - ineffassign
      - staticcheck
      - unused
      severity: warning

Output before the proposal

<?xml version="1.0" encoding="UTF-8"?>

<checkstyle version="5.0">
  <file name="internal/slack/slack_test.go">
    <error column="1" line="402" message="cognitive-complexity: function okFileUpload has cognitive complexity 17 (&gt; max enabled 15)" severity="info" source="revive">
    <error column="1" line="402" message="cyclomatic: function okFileUpload has cyclomatic complexity 14 (&gt; max enabled 12)" severity="info" source="revive">
    </error>
  </file>
</checkstyle>

With this proposal we add an exclude-linters to skip the default-severity

linters:
  disable-all: true
  enable:
    - errcheck
    - gosimple
    - govet
    - ineffassign
    - staticcheck
    - unused
    - revive
 
linters-settings:
  revive:
    severity: error
    rules:
      - name: cognitive-complexity
        arguments: [15]
      - name: cyclomatic
        arguments: [12]
        severity: warning

severity:
  default-severity: info
  exclude-linters:
    - revive
  rules:
    - linters:
      - errcheck
      - gosimple
      - govet
      - ineffassign
      - staticcheck
      - unused
      severity: warning

Output after the proposal

<?xml version="1.0" encoding="UTF-8"?>

<checkstyle version="5.0">
  <file name="internal/slack/slack_test.go">
    <error column="1" line="402" message="cognitive-complexity: function okFileUpload has cognitive complexity 17 (&gt; max enabled 15)" severity="error" source="revive">
    <error column="1" line="402" message="cyclomatic: function okFileUpload has cyclomatic complexity 14 (&gt; max enabled 12)" severity="warning" source="revive">
    </error>
  </file>
</checkstyle>

I didn't write any tests for this yet, I simply tested it locally to validate the output files.

Let me know if this is something worth to put more effort and I will happily finalize the work.

[boring-cyborg]

Hey, thank you for opening your first Pull Request !

[CLAassistant]

All committers have signed the CLA.

[ldez]

Hello,

The only linter that produces severity is revive.
The revive has its system to define and set severities.

I think it's better not to override severities when severity already exists like that:

	return transformIssues(issues, func(i *result.Issue) *result.Issue {
		if i.Severity != "" {
			return i
		}

In this context, we don't need a new option but just to add the previous 3 lines.

[ldez]

I created PR #4451 to simplify the severity processor code.

After that, I will create a PR that adds the option keep-linter-severity.
If set to true, the severities from linters are not overridden.
This option is just to be non-breaking.

severity:
  default-severity: tomato
  keep-linter-severity: true # <--

--> #4452

[ealves-pt]

Awesome @ldez!

Thank you so much for the feedback and the speed tackling it.