Inline functions that do mutation rejected as ghost

[vkuncak]

Inline functions that do mutation rejected as ghost

[mario-bucev]

What a strange error, I've checked against an older commit and the same error appears, at least it's not from #1476...

[vkuncak]

The intention of having user-defined change blocks using inline seems doomed, but it helped uncover this.
Trying to make things ghost also confused me. It seems that marking an entire class ghost does not make its mutable fields ghost, but only methods defined in it (if any)? Do we have examples of people putting ghost on a class?

[mario-bucev]

changeMyClass is annotated with @ghost here because it is "an erased value or an erased inline method or field" according to the doc of isEffectivelyErased.
This check has been added here when we could use erased as a replacement for @ghost. Note that this check to isEffectivelyErased has no equivalent in the Scala 2 frontend.
I think it is safe to allow inline method, since this check was surely meant to only include erased.