More checks of argument aliasing

[jad-hamza]

For issue #947

@samarion I tried your suggestion of using Try(getTargets(e)).toOption.getOrElse(exprOps.variablesOf(arg).map(v => Target(v, None, Path.empty)))) to identify aliases. Did you then want to check whether a target of one argument is a prefix of a target of another argument?

For issue #947, this doesn't seem to work because the targets of c1 are Some(Target(c1, None, <empty>)) and the targets of c2 are Some(Target(c1, None, <empty>)). Should getTargets on c2 also return c1?

We might have the same issue with getTargets returns None, because variablesOf will not capture the transitive dependencies.

[samarion]

I tried your suggestion of using Try(getTargets(e)).toOption.getOrElse(exprOps.variablesOf(arg).map(v => Target(v, None, Path.empty)))) to identify aliases.

You might want to filter out variables that don't have a mutable type in the orElse case.

Did you then want to check whether a target of one argument is a prefix of a target of another argument?

Yes, that sounds right.

For issue #947, this doesn't seem to work because the targets of c1 are Some(Target(c1, None, )) and the targets of c2 are Some(Target(c1, None, )).

You probably need to apply rewritings with exprOps.replaceFromSymbols(env.rewritings, arg) before calling getTargets and variablesOf. That should hopefully fix the issue of transitive dependencies. If it doesn't, then we probably have a more general problem with aliasing in let-bindings.

[jad-hamza]

Thanks for the quick review! The rewritings make this example work correctly (make it fail as it should).

[jad-hamza]

I disabled the aliasing check for accessors, otherwise it was making simple updates such as x = x + 1 for a var x in a trait fail.