Comment 1:

The copy built-in function is explained in detail, with examples, in §Copying slices,
The Go Programming Language Specification.
http://golang.org/doc/go_spec.html#Copying_slices
One of the rules given in the specification is: "The built-in function copy copies
array or slice elements from a source src to a destination dst ..." The error message
"arguments to copy must be slices or array pointers" indicates that your code broke
this rule. You did not provide an example of your failing code.
[]byte is a slice type. Therefore, your proposed error messsage, "argument 1 is
invalid because it is a []byte which is not a slice or an array pointer," after
substitution, would read, "argument 1 is invalid because it is a slice[sic] which is
not a slice or an array pointer."

Comment 2:

Labels changed: added compilerbug.

Owner changed to r...@golang.org.

Status changed to Accepted.

Comment 3:

Sorry for not providing examples. Here is one:
package main
func main() {
    var a [4]byte
    var b [4]byte
    copy(a,b) // fails
    copy(&a,&b) // works
}
It may be obvious to a go expert that an array is not a slice or an array pointer, but
it 
is not necessarily obvious to an inexperienced go developer. The language does so 
much to hide the difference between pointer and reference and array that the 
inexperienced developer may not realize what to do to solve the problem.
That's why a hint from the compiler as to which arguments are causing the problem 
and what the incorrect type is would help the developer correct their code.

Comment 4:

This issue was closed by revision 07fc145.

Status changed to Fixed.

Merged into issue #-.