compiler fails to detect unimplemented method for embedded interface in struct, causing panic: invalid memory address or nil pointer dereference

[gopherbot]

by cyle@riggsfamilyweb.net:

Before filing a bug, please check whether it has been fixed since the
latest release. Search the issue tracker and check that you're running the
latest version of Go:

Run "go version" and compare against
http://golang.org/doc/devel/release.html  If a newer version of Go exists,
install it and retry what you did to reproduce the problem.

Thanks.

What steps will reproduce the problem?
If possible, include a link to a program on play.golang.org.
1. http://play.golang.org/p/cvmtnB4NoX

What is the expected output?
Some error about a missing/unimplemented method

What do you see instead?
Program compiles and runs with panic:
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x20 pc=0x203c]

goroutine 1 [running]:
main.main()
    /Users/cyler/src/gobug/bug.go:13 +0x3c

goroutine 2 [runnable]:
exit status 2


Which compiler are you using (5g, 6g, 8g, gccgo)?
 ~/src/gobug $ go version
go version go1.1.2 darwin/amd64

Which operating system are you using?
OS X 10.8.4 Darwin Kernel Version 12.4.0: Wed May  1 17:57:12 PDT 2013;
root:xnu-2050.24.15~1/RELEASE_X86_64 x86_64

Which version are you using?  (run 'go version')
 ~/src/gobug $ go version
go version go1.1.2 darwin/amd64

Please provide any additional information below.

Notes:
If the interface embedded in the struct is in a different file than the struct itself
the stack dump for the panic reports a call at line 0 of the file which defines the
interface.

[remyoudompheng]

Comment 1:

The method is not missing. I don't know what an unimplemented method is. You can't call
methods that don't exist.
Calling a method on a nil interface is a run-time panic (I can't find the right line in
the spec.=).
Incorrect line numbers are already reported (issue #4388)

Status changed to WorkingAsIntended.

[gopherbot]

Comment 2 by cyle@riggsfamilyweb.net:

Thanks for the quick response.

[remyoudompheng]

Comment 3:

http://golang.org/ref/spec#Selectors
"5. If x is of interface type and has the value nil, calling or evaluating the method
x.f causes a run-time panic."

[gopherbot]

Comment 4 by cyle@riggsfamilyweb.net:

For those looking at this in the future, I guess the following applies here?
http://golang.org/ref/spec#Calls :
"Calling a nil function value causes a run-time panic."
Although obvious in hindsight, it was not immediately obvious that not implementing a
method which exists on the interface is "calling a nil function".

[remyoudompheng]

Comment 5:

No it doesn't. There is no nil function involved here.

[gopherbot]

Comment 6 by cyle@riggsfamilyweb.net:

Thanks for the clarification.