cmd/gc: composite literal import regression after e73800eb2b00

[davecheney]

What steps will reproduce the problem?

https://golang.org/cl/7395054 has introduced a regression in juju similar to
the one it was trying to fix, at or after revision e73800eb2b00 I see the following when
trying to compile

# launchpad.net/juju-core/state/statecmd
state/statecmd/config.go:12: cannot use &txn.Op literal (type *txn.Op) as type
txn.Op in return argument
launchpad.net/juju-core/worker/uniter/relation
# launchpad.net/juju-core/worker/uniter/charm
worker/uniter/charm/charm.go:11: cannot use &txn.Op literal (type *txn.Op) as type
txn.Op in return argument

config.go:12 is import "launchpad.net/juju-core/state"
charm.go:11 is the same

What is the expected output? What do you see instead?


Please use labels and text to provide additional information.

[rsc]

Comment 1:

This is much harder than it should be. I wonder if it might help to export
&T{...} as (*T){...} instead. That's what the parse tree wants it to be.

[remyoudompheng]

Comment 2:

Revision e73800eb2b00 is ugly. I think the correct way of fixing (which is what I
originally intended), is to add a n->orig node when typechecking a &T{} literal. There
is so much mutation happening afterwards that I don't understand how it can work
otherwise.
I've begun to write https://golang.org/cl/7437043
It needs a bit more polishing and seems to compile juju, but haven't got the time to
reduce your issue to a small testcase.

[rogpeppe]

Comment 3:

7437043 fixes the juju problem, at any rate.

[rogpeppe]

Comment 4:

in case it helps, i narrowed down the juju code to the minimal amount that still
exhibits the problem. it might be possible to make it smaller still, of course, but i'm
stopping here.
i ended up with three files; running "go test" in the state directory shows the problem.
local/foo/foo.go:
package foo
type Op struct {}
state/state_test.go:
package state_test
import "launchpad.net/juju-core/state0"
type Foo *state.State
state/state.go:
package state
import "local/foo"
func Public() {
    var s Settings
    s.op()
}
type State struct {}
func (s *State) x(*Settings) {}
type Settings struct {}
func (c *Settings) x() {
    run([]foo.Op{{}})
}
func run([]foo.Op) {}
func (s *Settings) op() foo.Op {
    return foo.Op{}
}

[remyoudompheng]

Comment 5:

Thanks roger, I've updated CL 7437043 with your example.

[remyoudompheng]

Comment 6:

This issue was closed by revision b0bb6f8.

Status changed to Fixed.