http://d.puremagic.com/issues/show_bug.cgi?id=2029

           Summary: Typesefe variadic functions don't work at compile time
           Product: D
           Version: 2.013
          Platform: PC
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla@digitalmars.com
        ReportedBy: bartosz@relisoft.com


The following doesn't compile:

string foo (string [] a...)
{
    string result = "";
    foreach (s; a)
        result ~= s;
    return result;
}

mixin (foo ("int ", "x;"));

tError: cannot evaluate foo(cast(invariant(char)[][])((invariant(char)[][2u]
__arrayArg244 = void;
) , (__arrayArg244[0u]) = "int " , (__arrayArg244[1u]) = "x;" , __arrayArg244))
at compile time
attribute argument to mixin must be a string, not
(foo(cast(invariant(char)[][])
((invariant(char)[][2u] __arrayArg244 = void;
) , (__arrayArg244[0u]) = "int " , (__arrayArg244[1u]) = "x;" ,
__arrayArg244)))


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Tomas Lindquist Olsen <tomas@famolsen.dk> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tomas@famolsen.dk


--- Comment #1 from Tomas Lindquist Olsen <tomas@famolsen.dk> 2009-09-15 07:15:10 PDT ---
I'd like this to work too :) I guess I should make a patch ...

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Version|2.013                       |1.020


--- Comment #2 from Don <clugdbug@yahoo.com.au> 2009-09-15 07:30:43 PDT ---
(In reply to comment #1)
> I'd like this to work too :) I guess I should make a patch ...

I had a quick go at it before the last release. I didn't include it because it required changes outside of interpret.c. So I did member functions instead <g>. Should work on D1 as well.

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--- Comment #3 from Don <clugdbug@yahoo.com.au> 2009-09-15 07:42:03 PDT ---
(In reply to comment #2)
> (In reply to comment #1)
> > I'd like this to work too :) I guess I should make a patch ...
> 
> I had a quick go at it before the last release. I didn't include it because it required changes outside of interpret.c. So I did member functions instead <g>. Should work on D1 as well.

To clarify: you can just comment out the lines near the top of interpret.c that
displays the error message about typesafe variadics. But then you find that it
doesn't compile, because it's trying to modify a global variable __arrayArg1.
(The CTFE error messages make it a lot easier to understand what's happening
<g>).
Something similar happens with struct constructors, and I think it's wrong.
It's more difficult to know how to fix it without breaking something else.

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--- Comment #4 from Tomas Lindquist Olsen <tomas@famolsen.dk> 2009-11-18 03:40:17 PST ---
Created an attachment (id=501)
draft patch for fixing typesafe variadic and ctfe

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--- Comment #5 from Tomas Lindquist Olsen <tomas@famolsen.dk> 2009-11-18 03:46:13 PST ---
I've attached a draft patch that replaces the typesafe variadic ast rewrites to something that works in any scope (and with ctfe).

without the patch the following function:

    void foo(int[] arr ...)

when called:

    foo(1,2,3);

is rewritten as:

    int[3] _args;
    (_args[0] = 1, _args[1] = 2, _args[2] = 3, foo(_args[]));

..

In global scope, this breaks, as you cannot assign to globals from ctfe, and in normal ctfe, breaks somehow as well.

This patch changes the rewrite to:

    foo([1,2,3]);

with each element being implicitly converted to the array element type.

One downside is that codegen always allocates array literals on the heap, so it degrades performance a bit, but that needs to be fixed for http://d.puremagic.com/issues/show_bug.cgi?id=2356 as well (though it's probably a slightly different issue), and generally I'm not getting an impression that it's a concern (performance is secondary).

In any case I added a new "scopedLiteral" field to ArrayLiteralExp so that codegen knows it's allowed to put the array on the stack if it wants to.

Comments appreciated.

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--- Comment #6 from Tomas Lindquist Olsen <tomas@famolsen.dk> 2009-11-18 03:48:50 PST ---
I forgot to mention, the patch is against the latest dmd-1.x branch

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--- Comment #7 from Tomas Lindquist Olsen <tomas@famolsen.dk> 2009-11-21 06:21:44 PST ---
So... Noone cares?

... This is a *draft*. I'm looking for feedback on how to better fix this, while the patch isn't perfect, it does fix the bug.

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--- Comment #8 from Don <clugdbug@yahoo.com.au> 2009-11-25 21:23:48 PST ---
Thanks, this is helpful. The problem is, that this isn't an isolated bug: the struct constructor bug has the same root cause. I think we need to fix both of them at once.

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--- Comment #9 from Don <clugdbug@yahoo.com.au> 2009-12-23 01:34:48 PST ---
The solution is much, much simpler. The problem is that CTFE doesn't support casting array literals to their base type, even though it's a no-op!


constfold.c, inside Expression *Cast(Type *type, Type *to, Expression *e1),
line 1095:
------------
    /* Allow casting from one string type to another
     */
    if (e1->op == TOKstring)
    {
    if (tb->ty == Tarray && typeb->ty == Tarray &&
        tb->nextOf()->size() == typeb->nextOf()->size())
    {
        return expType(to, e1);
    }
    }

+    if (e1->op == TOKarrayliteral && typeb == tb)
+        return e1;

    if (e1->isConst() != 1)
    return EXP_CANT_INTERPRET;
--------
And then in interpret.c, we can remove the error message (line 116):

    TypeFunction *tf = (TypeFunction *)tb;
    Type *tret = tf->next->toBasetype();
-    if (tf->varargs)
-    {    cantInterpret = 1;
-    error("Variadic functions are not yet implemented in CTFE");
-    return NULL;
-    }
    // Ensure there are no lazy parameters
    if (tf->parameters)

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