[Issue 5164] New: Error without line number using "is (T...)"

November 06, 2010
[Issue 5164] Error without line number using "is (T...)"
Posted by Don
in reply to Don
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Don
Posted in reply to Don
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http://d.puremagic.com/issues/show_bug.cgi?id=5164


Don <clugdbug@yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch
           Severity|normal                      |major


--- Comment #1 from Don <clugdbug@yahoo.com.au> 2010-11-05 23:22:56 PDT ---
There are multiple problems here:
(1) The missing line number is because in declaration.c, line 157, 'loc' never
gets stored:

TupleDeclaration::TupleDeclaration(Loc loc, Identifier *id, Objects *objects)
    : Declaration(id)
{
+    this->loc = loc;
    this->type = NULL;
    this->objects = objects;

(2) The error message happens because in IsExp::semantic(), around line 5130,
in the "declare trailing parameters" section, the symbol is added TWICE. First
as:
        sc->insert(s);
   and later as
        s->addMember(sc, sc->sd, 1);
For every other pooible symbol in an is(), it recognizes it's a duplicate and
doesn't raise an error, but TupleDeclaration doesn't define overloadInsert, so
it fails. But I don't think it should be adding twice in the first place.

The difference between insert() and addMember() is that the latter allows code
such as this:

struct boo(T...) {}

template foo(T){
    static if (is(T xxx == boo!(U), U...) ) {}
       enum result = true;
}

foo!(boo!(int)).U[0] yyy;

That is, it makes the declared symbol accessible outside the template. But if it's a struct foo(T), the U symbol is accessible in both cases. So I think the call to sc->insert(s) should be moved to the end, and called only if addMember isn't called. Line 5145.

-                if (!sc->insert(s))
-                    error("declaration %s is already defined", s->toChars());
#if 0
                Object *o = (Object *)dedtypes.data[i];
                Dsymbol *s = TemplateDeclaration::declareParameter(loc, sc, tp,
o);
#endif

   if (sc->sd)
        s->addMember(sc, sc->sd, 1);
+    else if (!sc->insert(s))
+        error("declaration %s is already defined", s->toChars());


(3) Although the example in point 2 now compiles, it generates wrong code! The tuple will always be empty. This is because the earlier correctly deduced tuple is getting clobbered. This happens in template.c, line 3510


   MATCH TemplateTupleParameter::matchArg(Scope *sc,
        Objects *tiargs, int i, TemplateParameters *parameters,
        Objects *dedtypes,
        Declaration **psparam, int flags)
{
    //printf("TemplateTupleParameter::matchArg()\n");

    /* The rest of the actual arguments (tiargs[]) form the match
     * for the variadic parameter.
     */
    assert(i + 1 == dedtypes->dim);     // must be the last one
    Tuple *ovar;
+                // It might have already been deduced
+    if (dedtypes->data[i] && isTuple((Object *)dedtypes->data[i]))
+        ovar = isTuple((Object *)dedtypes->data[i]);
    else
    if (i + 1 == tiargs->dim && isTuple((Object *)tiargs->data[i]))
        ovar = isTuple((Object *)tiargs->data[i]);

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