In directory $GOROOT/src:

$ gorename -from \"cmd/internal/obj/arm64\"::c -to ___ -d
gorename: ambiguous specifier c matches var at asm7.go:6, var at asm7.go:6, var at asm7.go:2, var at asm7.go:5, var at asm7.go:43, var at asm7.go:2

The positions here are bogus; there is no object c at any of these places. These appear to be line offsets relative to functions containing local variables called c.

There's also an implicit feature request here. I'm running this command to find all the local variables named c. Then I will inspect them, pick a good new name for them, and gorename them one at a time. The -to=___ is just because a -to is required, and -d is to avoid actually changing the files; I don't really want any of that, I just want to know where the c's are. Maybe there's a better way? Perhaps a gorename flag that just tells you the declaration site of all impacted objects?

cc @alandonovan