False-positives alerts for interface type conversions

[Ragnar-BY]

Last version golangci-lint use errcheck v1.8.0
Now errcheck gives alerts for code like:

	var a interface{}
	a = 5

	switch a.(type) {
	case string:
		fmt.Println("this is string", a.(string))
	case int:
		fmt.Println("this is int", a.(int))
	default:
		fmt.Println("unknown type")
	}

I think it is related to changes from #246
I believe that it is false-positive, because type is checked in switch-case

[kisielk]

Here's a test case if someone wants to have a crack at fixing this:

--- a/errcheck/testdata/src/assert/main.go
+++ b/errcheck/testdata/src/assert/main.go
@@ -1,5 +1,7 @@
 package assert
 
+import "fmt"
+
 func main() {
        var i interface{}
        _ = i.(string) // want "unchecked error"
@@ -16,6 +18,18 @@ func main() {
                _ = i.(int) // want "unchecked error"
        case nil:
        }
+
+       var a interface{}
+       a = 5
+
+       switch a.(type) {
+       case string:
+               fmt.Println("this is string", a.(string))
+       case int:
+               fmt.Println("this is int", a.(int))
+       default:
+               fmt.Println("unknown type")
+       }
 }

[dtcaciuc]

Current errcheck behavior is consistent with gopls. Recommended action is to reassign variable to make it assume the resolved type