cmd/compile: cannot use &autotmp_1621 (type *error) as type *parseError in argument to runtime.assertE2T2

[bep]

See failed Travis build for Viper:

https://travis-ci.org/spf13/viper/jobs/128640109

github.com/BurntSushi/toml

# github.com/BurntSushi/toml

../../BurntSushi/toml/parse.go:43: cannot use &autotmp_1621 (type *error) as type *parseError in argument to runtime.assertE2T2

Works on 1.4-1.6, fails on Go tip.

See https://github.com/BurntSushi/toml/blob/master/parse.go#L43

[dr2chase]

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

[josharian]

That sure suggests 9d7c9b4

[josharian]

cc @mdempsky @tshprecher

[josharian]

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.

[mdempsky]

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)
}

[gopherbot]

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

[mdempsky]

Reverted.

[josharian]

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

[josharian]

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

[mdempsky]

SGTM, go for it.