[Issue 6230] New: Member functions can no longer be weakly pure

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=6230

           Summary: Member functions can no longer be weakly pure
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: rejects-valid
          Severity: blocker
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: kennytm at gmail.com


--- Comment #0 from kennytm at gmail.com 2011-06-30 08:39:36 PDT ---
(See http://lists.puremagic.com/pipermail/phobos/2011-June/005487.html and
comments in Phobos commit 4f28d** for existing discussion.)

After DMD commit 84b4f* a member function can no longer be pure, claiming
itself as a nested function. I believe this is a bug because the relevant DMD
code

            Dsymbol *vparent = v->toParent2();
            for (Dsymbol *s = sc->func; s; s = s->toParent2())
            {
                if (s == vparent)
                    break;
                FuncDeclaration *ff = s->isFuncDeclaration();
                if (!ff)
                    break;
                if (ff->setImpure())
                {   error("pure nested function '%s' cannot access mutable data
'%s'",
                        ff->toChars(), v->toChars());
                    break;
                }
            }

cannot check the case when 'vparent' is an aggregrate. Nevertheless, this leads
to commits d014a and 40def in druntime, and 4f28d in Phobos**, which probably
means this bug is INVALID.

Test case:
-----------------------
struct S {
    int p;
    int q() const pure {    // <-- Error
        return p;
    }
}

class C {
    int p;
    int q() const pure {    // <-- Error
        return p;
    }
}

int q2(ref const S s) pure {    // <-- Currently OK
    return s.p;
}

int q3(ref const C c) pure {    // <-- Currently OK
    return c.p;
}
-----------------------
y.d(4): Error: pure nested function 'q' cannot access mutable data 'p'
y.d(11): Error: pure nested function 'q' cannot access mutable data 'p'
-----------------------

* https://github.com/D-Programming-Language/dmd/commit/84b4f
** https://github.com/D-Programming-Language/druntime/commit/d014a
   https://github.com/D-Programming-Language/druntime/commit/40def
   https://github.com/D-Programming-Language/phobos/commit/4f28d

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