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staticcheck: flag string(T) where T is a newtype of uint8 that has a String() method #1119
Description
(Filing separately from #682, since this is something outside of go vet's check; feel free to merge.)
package main
import "fmt"
type newtype uint8
func (v newtype) String() (s string) { return "newtype" }
func main() {
// Example A
fmt.Println(string(64))
// Example B
fmt.Println(string(newtype(64)))
// Example C
fmt.Println(newtype(64).String())
}go vet will mark example A but not example B, probably because it still allows string(byte) conversions and thinks that newtype is the same as byte.
staticcheck (as of v0.3.0-0.dev.0.20211107063326-8cad455d2ffe) doesn't report any errors. There is already an issue about reproducing the original go vet check, but I think that this one is different, because this one concerns newtypes, and in particular ones that have their own String() method. I think that if the programmer (1) defined a new type and (2) added a String() method for it then it is extremely unlikely that they would want string(T) as opposed to T.String() anywhere in their code.
(Also, apologies for opening a blank issue instead of using a template. A force of habit 😅.)
Activity
dominikh commentedon Nov 10, 2021
Marking as
aggressivebecause I'm not sure this would fit intostaticcheck, and marking asneeds-decisionbecause I'm not sure it fits at all. I can imagine valid code that would do this, for example in the context of binary serialization. The type would represent some field in a binary file format, its String method returns a human-friendly representation (such as the name of an enum), and string(b) would be used while building output to write. It's somewhat far-fetched, however, because binary serialization shouldn't be using strings.