[Issue 3869] Unreasonable error without line number: "recursive template expansion"

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=3869


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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
                 CC|                            |clugdbug at yahoo.com.au


--- Comment #1 from Don <clugdbug at yahoo.com.au> 2010-03-02 11:19:28 PST ---
The missing line number is the only bug here; the rest is an enhancement
request. You have a recursive definition in sum.opAdd(). As soon as you do
anything which forces opAdd to be instantiated, the recursion is detected.

Here's a reduced test case for what you're doing:

struct sum(A) {
    auto blah(int a) { return .sum!(sum)(); }
}

sum!(int) z;

-------
A quick, incomplete patch to improve the error message slightly: Template.c
line 156.
(Doesn't help very much, since it only gives the line number of the template
which is being instantiated, whereas you might want the line which was
instantiating it).
In fact, this particular test case will compile OK if the error message is
removed. (still need to return 1 to fake a match). But that won't work in
general.

    if (t1)
    {
    /* if t1 is an instance of ti, then give error
     * about recursive expansions.
     */
    Dsymbol *s = t1->toDsymbol(sc);
    if (s && s->parent)
    {   TemplateInstance *ti1 = s->parent->isTemplateInstance();
        if (ti1 && ti1->tempdecl == tempdecl)
        {
        for (Scope *sc1 = sc; sc1; sc1 = sc1->enclosing)
        {
            if (sc1->scopesym == ti1)
            {
-            error("recursive template expansion for template argument %s",
t1->toChars());
+            error(s->loc, "recursive template expansion for template argument
%s", t1->toChars());
            return 1;    // fake a match
            }
        }
        }
    }

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