runtime: val, ok = <- someChannel inside of select causes ok to be false on empty channel but not closed

[gopherbot]

by Chance.Zibolski:

Firstly, I want to mention this issue was found in go 1.2.2 and resolved in go 1.3, but
because I was unable to find a bug, or any mention of this problem in the release notes,
I was not very confident that the Go authors were aware of the bug existing or getting
fixed, because the lack of disclosure related to the issue.

The issue violates the spec "The value of ok is true if the value received was
delivered by a successful send operation to the channel, or false if it is a zero value
generated because the channel is closed and empty."

The actual behavior in go 1.2.2 is that the value is false when the channel is closed
*OR* empty.

Because there may be code running on 1.2.2 which expects the behavior to be the
"OR" (even though it isnt according the spec), I would have expected this to
be announced on the release, much like how map iteration became random.

I also expect that there would be a test to verify, and assert the proper behavior, but
I'm also unsure of that.

What does 'go version' print?

go1.2.2 linux/amd64

What steps reproduce the problem?

Use the val, ok idiom to receive from a non-closed channel which is empty, inside of a
select structure with a default case.

http://play.golang.org/p/zvPKOQeOD5
https://gist.github.com/ecnahc515/9c42754b8c4dfc27500f

What happened?

The value of okay was set to false.

What should have happened instead?

The value of okay should remain true.

Please provide any additional information below.

After talking to some people in #go-nuts who bisected, they seem to think the issue was
fixed here: https://golang.org/cl/83000048

[dominikh]

Comment 1:

To save some people the effort:
Go 1.0.2 (yes, that old) already had the wrong behaviour.
https://golang.org/cl/83000048 is the CL that eventually changed it.

[gopherbot]

Comment 2:

CL https://golang.org/cl/109600044 mentions this issue.

[gopherbot]

Comment 3 by Chance.Zibolski:

If there is a test and as I've found, its been fixed then this could be closed. However
I'm very surprised the was no announcement about this bug somewhere. Maybe I'm blind
though.

[ianlancetaylor]

Comment 4:

Labels changed: added repo-main, release-go1.4.

[robpike]

Comment 6:

This is reporting a bug that has been fixed in 1.3. I am unsure what the requester is
asking for. Is it just a test? If so, please submit a CL to add a test.

[gopherbot]

Comment 7 by Chance.Zibolski:

I'm not writing a test, but yes, I filed a bug because I didn't have much confidence
this bug was an intentionally fixed after reviewing what might have fixed this.

[minux]

Comment 8:

This issue was closed by revision 2296928.

Status changed to Fixed.