feat: syntax to not override severity from linters

[ldez]

When I created #4452, I thought that only one linter produced issues with severities.

But it's not true as you can see here #4470

The previous option was global: affects all the linters.

The first problem is that revive uses warning and error as severity, but gosec uses low, medium, and high.

I don't want to convert one to another because:

• 2 severities vs 3 severities
• some tools allow only the usage of specific severity
• it's not possible to say what is the best set of values for severities

The second problem is related to the fact that some tools allow only the usage of specific severity.
The current option will keep the severity value from all linters, then the values will be a mix of the different sets.

If you need to use only one set of severities, you need to override/replace the severities from the unsupported set of values.

Then, I reverted the previous PR #4452 (first commit) and replaced it with the usage of a specific wildcard value (@linter) as severity.

The value @ is inspired by some DNS convention, but we can use another character (* is ambiguous).

This value can be used as a default severity or as a rule severity.

One commit, one change.

---

The following examples illustrate the behavior.

the code sample

package main

import (
	"fmt"
	"os"
	"os/exec"
)

func main() {
	exec.Command("go", "help", os.Args[0])
}

func foo(s string) {
	fmt.Println("test")

}

no custom severities

linters:
  disable-all: true
  enable:
    - gosec
    - revive
    - wsl

linters-settings:
  revive:
    severity: error
    rules:
      - name: unexported-return
        disabled: true
      - name: unused-parameter
        severity: warning

$ ./golangci-lint run --out-format json | jq  '.Issues[] | {linter: .FromLinter, text: .Text, severity: .Severity }'
{
  "linter": "gosec",
  "text": "G204: Subprocess launched with a potential tainted input or cmd arguments",
  "severity": "medium"
}
{
  "linter": "revive",
  "text": "unused-parameter: parameter 's' seems to be unused, consider removing or renaming it as _",
  "severity": "warning"
}
{
  "linter": "wsl",
  "text": "block should not end with a whitespace (or comment)",
  "severity": ""
}

`@linter` as rule severity

linters:
  disable-all: true
  enable:
    - gosec
    - revive
    - wsl

linters-settings:
  revive:
    severity: error
    rules:
      - name: unexported-return
        disabled: true
      - name: unused-parameter
        severity: warning

severity:
  default-severity: tomato
  rules:
    - linters:
        - gosec
      severity: '@linter'

$ ./golangci-lint run --out-format json | jq  '.Issues[] | {linter: .FromLinter, text: .Text, severity: .Severity }'
{
  "linter": "gosec",
  "text": "G204: Subprocess launched with a potential tainted input or cmd arguments",
  "severity": "medium"
}
{
  "linter": "revive",
  "text": "unused-parameter: parameter 's' seems to be unused, consider removing or renaming it as _",
  "severity": "tomato"
}
{
  "linter": "wsl",
  "text": "block should not end with a whitespace (or comment)",
  "severity": "tomato"
}

`@linter` as default value

linters:
  disable-all: true
  enable:
    - gosec
    - revive
    - wsl

linters-settings:
  revive:
    severity: error
    rules:
      - name: unexported-return
        disabled: true
      - name: unused-parameter
        severity: warning

severity:
  default-severity: '@linter'
  rules:
    - linters:
        - gosec
      severity: carrot

$ ./golangci-lint run --out-format json | jq  '.Issues[] | {linter: .FromLinter, text: .Text, severity: .Severity }'
{
  "linter": "gosec",
  "text": "G204: Subprocess launched with a potential tainted input or cmd arguments",
  "severity": "carrot"
}
{
  "linter": "revive",
  "text": "unused-parameter: parameter 's' seems to be unused, consider removing or renaming it as _",
  "severity": "warning"
}
{
  "linter": "wsl",
  "text": "block should not end with a whitespace (or comment)",
  "severity": ""
}

Fixes #3111

[ldez]

Maybe @linter instead of @? 🤔

[alexandear]

I propose @inherit instead of @. Or we can use @linter.

[ldez]

@inherit seems ambiguous because it can be seen as inherited from the default severity.

[Antonboom]

👍