os: inconsistent behaviour of File's methods on a nil pointer

[gopherbot]

by robryk:

Some of *os.File's methods return an error when called on a nil pointer. For example,
the following do so: Read, ReadAt, Write, WriteAt. These methods explicitely check for a
nil pointer.

Some other panic when they are called on a nil pointer. For instance: Name, Close, Seek.

The documentation doesn't say anything about this case. It might be nice to do the same
thing for all methods, but I'm not sure if the compatibility promises don't prevent any
change there.

The behaviour was mentioned in:
https://plus.google.com/u/0/104862366695495126200/posts/LE5tfxKaUS4

[robpike]

Comment 1:

Labels changed: added priority-later, removed priority-triage.

Status changed to Accepted.

[rsc]

Comment 2:

Labels changed: added go1.2maybe.

[rsc]

Comment 3:

Labels changed: added feature.

[robpike]

Comment 4:

The change can only be made for methods that return an error, so Fd and Name are not
candidates.
The following program prints:
Chdir panicked
Chmod panicked
Chown panicked
Close panicked
Readdir panicked
Readdirnames panicked
Seek panicked
Stat panicked
Truncate panicked
package main
import (
    "fmt"
    "os"
)
func test(name string, f func()){
    defer func() {
        if recover() != nil {
            fmt.Println(name, "panicked")
        }
    }()
    f()
}
func main() {
    p := make([]byte, 10)
    test("Chdir", func(){(*os.File)(nil).Chdir()})
    test("Chmod", func(){(*os.File)(nil).Chmod(0)})
    test("Chown", func(){(*os.File)(nil).Chown(0, 0)})
    test("Close", func(){(*os.File)(nil).Close()})
    test("Read", func(){(*os.File)(nil).Read(p)})
    test("ReadAt", func(){(*os.File)(nil).ReadAt(p, 0)})
    test("Readdir", func(){(*os.File)(nil).Readdir(0)})
    test("Readdirnames", func(){(*os.File)(nil).Readdirnames(0)})
    test("Seek", func(){(*os.File)(nil).Seek(0, 0)})
    test("Stat", func(){(*os.File)(nil).Stat()})
    test("Sync", func(){(*os.File)(nil).Sync()})
    test("Truncate", func(){(*os.File)(nil).Truncate(0)})
    test("Write", func(){(*os.File)(nil).Write(p)})
    test("WriteAt", func(){(*os.File)(nil).WriteAt(p, 0)})
    test("WriteString", func(){(*os.File)(nil).WriteString("hi")})
}

[robpike]

Comment 5:

This issue was closed by revision 4cb086b.

Status changed to Fixed.