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digitalmars.D.bugs - [Issue 7372] New: wrong error: undefined identifier

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7372

           Summary: wrong error: undefined identifier
           Product: D
           Version: D1
          Platform: x86
        OS/Version: Linux
            Status: NEW
          Severity: regression
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: leandro.lucarella sociomantic.com



2012-01-26 08:50:37 PST ---
Test case:

m.d
---
import m2;
interface I {}
class C : I { mixin M!(I); }
---

m2.d
----
import m1;
template M (T)
{
    public void f()
    {
        bug(1); // line 6
    }
}
----

m1.d
----
template bug(T)
{
    void bug(T t) {}
}
----

$ dmd -c m.d
m2.d(6): Error: undefined identifier bug
m2.d(6): Error: function expected before (), not __error of type _error_

Aside from the second spurious error, "bug" symbol should be perfectly defined.

Moving any template function to another module fixes the problem. Using a
selective import (import m1 : bug;) also fails. Using the full name of the
symbol (m1.bug(1); using static import m1; or without static) produces this
error instead:

m2.d(6): Error: undefined identifier m1, did you mean module m?
m2.d(6): Error: function expected before (), not __error of type _error_

Adding an alias to m2.d like this: alias m1.bug bug; fixes the problem. So it
looks like the symbol is hidden to the template.

A git bisect show this commit as the one introducing the regression:
merge D2 pull 591 (93a643aba6f62db1b7658c2bfb51f9d0b576c337)

https://github.com/D-Programming-Language/dmd/commit/93a643aba6f62db1b7658c2bfb51f9d0b576c337
https://github.com/D-Programming-Language/dmd/pull/591

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7372


Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bugzilla digitalmars.com
         Resolution|                            |INVALID



12:25:59 PST ---
This is not a bug.

From the spec: "Unlike a template instantiation, a template mixin's body is
evaluated within the scope where the mixin appears, not where the template
declaration is defined."

The default for imports is private, so m1.bug is not visible to m.C.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7372


Leandro Lucarella <leandro.lucarella sociomantic.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|rejects-valid               |diagnostic
             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |
            Summary|(Regression git) wrong      |Error provides too little
                   |error: undefined identifier |information to diagnose the
                   |                            |problem (error: undefined
                   |                            |identifier)
           Severity|regression                  |normal



2012-01-27 04:00:32 PST ---


 This is not a bug.
 
 From the spec: "Unlike a template instantiation, a template mixin's body is
 evaluated within the scope where the mixin appears, not where the template
 declaration is defined."
 
 The default for imports is private, so m1.bug is not visible to m.C.


OK, so the case with the alias works because aliases are public by default,
right? Then using private alias m1.bug bug; I get this error:
m2.d(7): Error: module m m2.bug is private

Which describes the problem a little better. I will reopen this (lowering the
importance) to keep in mind the error message should be improved. The current
error gives no NO clue about the real location of the problem, which should be
the instantiation site, I think.

The "private alias" error is a little better in that regard but could be more
specific too. This is the main reason why this problem was SO hard to reduce to
a small test case. I was extremely hard to find out where the root problem was
because the error is triggered in the template, which in the real code is
instantiated from many places.

Besides that, I think this is a really nasty corner case then. So using a mixin
will require either:

1) Pollute the user's namespace by publicly importing everything the template
use
2) Asking the user to know the details of the mixin implementation and import
things according.

It there any other solution to this problem that doesn't have those 2 problems?
I guess doing the imports INSIDE the template would be an option, thus
polluting only the class name space and not the entire module, but there is
still pollution going on.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement



09:28:10 PST ---
It's fundamental to mixing in templates that any scopes it needs to build must
be present in the instantiation context, so yes, the burden is on the designer
of that template to document it.

I'm going to mark this as enhancement because it is working as it was designed
to.

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prev sibling parent d-bugmail puremagic.com writes:
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2012-01-27 09:35:15 PST ---


 It's fundamental to mixing in templates that any scopes it needs to build must
 be present in the instantiation context, so yes, the burden is on the designer
 of that template to document it.
 
 I'm going to mark this as enhancement because it is working as it was designed
 to.


Fair enough, but I think the error is really bad, I spent at least 2 hours to
figure out what was going on because of what I explain in comment 2. I  I think
it might deserve a little more than "enhancement", but this is a grey area. If
a compiler error says "can't compile" and nothing else, is that an bug or just
an enhancement? The message is not wrong, but is really bad, like in this case
(at a different level, of course).

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