exclude maphash methods that "never fail"

[djdv]

These methods are documented to "never fail", so it should be okay to ignore the return values.

hash.Hash is already excluded, but unlike the other subpkgs of hash, hash/maphash doesn't follow the convention of using a New() hash.Hash constructor; instead it exposes a struct *maphash.Hash, who's methods are called directly.

Since this is part of the standard library and likely to be called in this way, it seemed appropriate to add them to the default exclusion list.
You think so?

[kisielk]

Seems right to me.

[djdv]

Cool 😎
I tested this commit manually against the original code I was linting, as well as this:

package main
import "hash/maphash"
func main() {
	var hasher maphash.Hash
	hasher.Write(nil)
	hasher.WriteByte(0)
	hasher.WriteString("")
}

and it seems to detect (and exclude) the signatures correctly.

[dtcaciuc]

@djdv Do you mind adding a test case? You can either add those calls to an existing function under testdata or make a new one just for hashmaps (as long as its in main package)

[djdv]

I wasn't so sure how to add this test case, is something like this right?
If so, maybe it also makes sense to include c277fb1 but if not it could be dropped.

Edit:
I was hesitant about this because running go test was yielding this error before and after these patches:

internal error: package "crypto/sha256" without types was imported from "github.com/kisielk/errcheck/testdata"

Turns out I was running the tip build of the go command (oops).
Running the tests on Go stable seems to work as expected. The tests fail before the patch, but not after.

[dtcaciuc]

Looks good, thank you!