This worked with Friday's tip (+83676d6) but now fails nicely for me.

That sure suggests 9d7c9b4

cc @mdempsky @tshprecher

Given that the bug that that CL was fixing is not a regression from 1.6 (it was broken in 1.5 and 1.6), and given Russ's instructions for the code freeze, I suggest we re-open that issue, roll back the buggy fix, add a test case from this issue (closing it in the process), and then re-fix during the 1.8 cycle.

Agreed with @josharian. Revert 9d7c9b4 for 1.7, and try again for 1.8.

In retrospect, I suspect the issue is just the temporary variables need to match the RHS's type, not the LHS's type, but I don't want to try to roll forward with the problem now.

Minimal repro:

package p

func f(i interface{}) {
        i, _ = i.(error)
}

CL https://golang.org/cl/22930 mentions this issue.

Reverted.

I think this should be closed by a CL adding the minimal reproduction case you identified. That test will pass, and will prevent regression.

I'll mail such a CL in a bit if you don't beat me to it.

SGTM, go for it.

CL https://golang.org/cl/22931 mentions this issue.