fix Issue 16589 - Taking address of stack variables in @safe code is …

[WalterBright]

…allowed in some cases

[dlang-bot]

Fix	Bugzilla	Description
✓	16589	Taking address of stack variables in @safe code is allowed in some cases

[mathias-lang-sociomantic]

Should it be part of -transition=safe ?

[WalterBright]

Unfortunately, yes, as it is tripping in Phobos.

[mihails-strasuns]

Isn't it unnecessarily limiting though to implement this separately from DIP1000? It is perfectly valid to take address of the field and pass it to some function (expecting pointer) for processing, I would be very surprised if there isn't plenty of such code in the wild. Thus if it gets merged alone, it would break some legit use cases without a tool to make it work again (== scope).

[WalterBright]

It's been an error for years to take the address of a local in @safe code. It does not make sense to allow taking the address of a field of a local. This was not checked for, and that's what this PR does. It is not part of DIP1000.

It does break at least one Phobos function (the autotester quits at the first error), which is why I amended it to only check if -transition=safe, but the code is incorrect. Allowing this in @safe code breaks the whole point of ref.

If the user needs to & a local, the way to do it is by ref instead, or make it @trusted.

BTW, this rule nicely resolves the ambiguity of what return refers to with a parameter marked as return ref scope. If the function returns by ref, the return applies to the ref.

[andralex]

Few nits to improve the lot of readers and reduce LOC.

[andralex]

if (!v)
    return true; // nuttin' to do
... rest of the code ...

[andralex]

if + if = &&

if (sc.func && !sc.intypeof && !v.isDataseg() && sc.func.setUnsafe())
{
    ...
}

[andralex]

if (v && !checkAddressVar(v))
    return new ErrorExp();

[andralex]

if (v && v.storage_class & STCref) && !checkAddressVar(v))
    return new ErrorExp();

[andralex]

if (v && !checkAddressVar(v))
    return new ErrorExp();

[WalterBright]

Auto-merge toggled on