Error return value is not checked (errcheck) for interface assertion

[seaguest]

Hello,

seaguest@DEV:~/Work/monitor/test$ golangci-lint version
golangci-lint has version 1.51.2 built from 3e8facb4 on 2023-02-19T21:43:54Z
seaguest@DEV:~/Work/monitor/test$ 
seaguest@DEV:~/Work/monitor/test$ 
seaguest@DEV:~/Work/monitor/test$ cat t4.go
package main

import (
    "errors"
)

var _ error = (*ValidationError)(nil)

type ValidationError struct {
    Msg string
}

func (v *ValidationError) Error() string {
    return v.Msg
}

func main() {
    foo("huu")
}

func foo(a string) error {
    if a == "a" {
        return errors.New("OOPS")
    }

    return nil
}
seaguest@DEV:~/Work/monitor/test$ golangci-lint run -Eerrcheck 
t4.go:7:5: Error return value is not checked (errcheck)
var _ error = (*ValidationError)(nil)
    ^
t4.go:18:5: Error return value is not checked (errcheck)
    foo("huu")
       ^

There should not be error for

var _ error = (*ValidationError)(nil)

It seems related to https://github.com/kisielk/errcheck/pull/219

[meteorgan]

This problem exists because errcheck doesn't recognize the value of type conversion. It only checks if the result value is error type