[Bug c++/41970] New: Unjustified "anonymous type" warning

[Bug c++/41970] New: Unjustified "anonymous type" warning

[igodard at pacbell dot net]

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This code:

enum {a, b, c} A = a;
namespace {
    enum {d, e, f} D = d;
    }
int main() { return 0; }

gets you:

foo.cc:1: warning: non-local variable ‘<anonymous enum> A’ uses anonymous type
foo.cc:3: warning: non-local variable ‘<unnamed>::<anonymous enum>
<unnamed>::D’ uses anonymous type

As A is local and D is not, it seems that one of the warnings is wrong. Or
maybe the warning doesn't mean what it appears to mean, in which case please
consider this to be a report about an incomprehensible diagnostic.


-- 
           Summary: Unjustified "anonymous type" warning
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: igodard at pacbell dot net


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] Unjustified "anonymous type" warning

[redi at gcc dot gnu dot org]

------- Comment #1 from redi at gcc dot gnu dot org  2009-11-06 14:09 -------
Both declarations are at namespace-scope (see [basic.scope.namespace]) not
local scope (see [basic.scope.local]) so I think "non-local" is fine


-- 

redi at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] Unjustified "anonymous type" warning

[igodard at pacbell dot net]

------- Comment #2 from igodard at pacbell dot net  2009-11-06 15:30 -------
OK, I read the standard sections cited and understand.

Then I'll reopen this to ask the deeper question: why do either deserve a
warning in the first place? 


-- 

igodard at pacbell dot net changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] Unjustified "anonymous type" warning

[redi at gcc dot gnu dot org]

------- Comment #3 from redi at gcc dot gnu dot org  2009-11-06 15:43 -------
(In reply to comment #2)
> Then I'll reopen this to ask the deeper question: why do either deserve a
> warning in the first place? 

Good question - they probably should be fatal errors :-)

[basic.link]/8
"A name with no linkage (notably, the name of a class or enumeration declared
in a local scope (3.3.2)) shall not be used to declare an entity with linkage."

The anonymous enumeration types have no linkage, but one could argue that since
they are anonymous they are not "names with no linkage" but I think it's still
invalid.  If A and D have external linkage then they could be referred to from
another translation unit, but that is not possible because their type cannot be
named from another translation unit.

You can make it valid by giving the variables internal linkage:

enum {a, b, c} static A = a;
namespace {
    enum {d, e, f} static D = d;
    }


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] Unjustified "anonymous type" warning

[redi at gcc dot gnu dot org]

------- Comment #4 from redi at gcc dot gnu dot org  2009-11-06 15:48 -------
Or rather,

static enum {a, b, c} A = a;
namespace {
    static enum {d, e, f} D = d;
}


In any case, the warning is telling you that an object with external linkage
cannot be referred to in other translation units, so external linkage may not
be appropriate


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] Unjustified "anonymous type" warning

[igodard at pacbell dot net]

------- Comment #5 from igodard at pacbell dot net  2009-11-06 18:22 -------
That argument (warn about unreferenceable names with external linkage) applies
here to enum A. However, because enum D is inside the anonymous namespace it
cannot be referenced from another unit anyway and so must have local (i.e.
static) linkage. Hence, as suggested by my original report, it seems reasonable
that there should be no warning on D.

Or am I misunderstanding the implications of the anonymous namespace, which I
had understood to be the C++ replacement for C's "static"? That is, in your
second example, isn't the "static" on D redundant?


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] Unjustified "anonymous type" warning

[redi at gcc dot gnu dot org]

------- Comment #6 from redi at gcc dot gnu dot org  2009-11-06 18:27 -------
Members of anonymous namespaces do not necessarily have internal linkage,
that's the point.  They are local to a translation unit, but can still have
external linkage.

N.B. for GCC 4.2 and later "Members of the anonymous namespace are now local to
a particular translation unit, along with any other declarations which use
them, though they are still treated as having external linkage for language
semantics."
>From http://gcc.gnu.org/gcc-4.2/changes.html


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] Unjustified "anonymous type" warning

[redi at gcc dot gnu dot org]

------- Comment #7 from redi at gcc dot gnu dot org  2009-11-06 18:30 -------
N.B. Comeau's online compiler gives an error for both variable definitions


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] Unjustified "anonymous type" warning

[matt at use dot net]

------- Comment #8 from matt at use dot net  2010-01-10 22:04 -------
Created an attachment (id=19531)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=19531&action=view)
pre-processed output of the file that emitted the false positive using the
commandline mentioned in my comment


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] Unjustified "anonymous type" warning

[igodard at pacbell dot net]

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------- Comment #9 from igodard at pacbell dot net  2010-01-10 22:23 -------
Comeau gives this diagnostic:
"ComeauTest.c", line 1: error: use of a type with no linkage to declare a
variable
          with linkage
  enum {a, b, c} A = a;
                 ^
This message give the true nature of the problem, whereas the gcc message:
  foo.cc:1: warning: non-local variable ‘<anonymous enum> A’ uses anonymous
type
requires six posts from experts to explain.

Please recategorize this report as "diagnostic quality", confirm, and assign
it.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] Unjustified "anonymous type" warning

[manu at gcc dot gnu dot org]

------- Comment #10 from manu at gcc dot gnu dot org  2010-01-11 18:46 -------
(From update of attachment 19531)
This file has nothing to do with this bug.


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #19531|0                           |1
        is obsolete|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] Unjustified "anonymous type" warning

[manu at gcc dot gnu dot org]

------- Comment #11 from manu at gcc dot gnu dot org  2010-01-11 18:52 -------
(In reply to comment #9)
> Please recategorize this report as "diagnostic quality", confirm, and assign
> it.

Bugs are not assigned, they are taken. But confirmed it is. Patches welcome.


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu dot org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |diagnostic
   Last reconfirmed|0000-00-00 00:00:00         |2010-01-11 18:52:09
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] use of a type with no linkage to declare a variable with linkage

[manu at gcc dot gnu dot org]

------- Comment #12 from manu at gcc dot gnu dot org  2010-01-11 18:54 -------
Comeau rejects it. Is this accepts-invalid, then?


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Unjustified "anonymous type"|use of a type with no
                   |warning                     |linkage to declare a
                   |                            |variable with linkage


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] use of a type with no linkage to declare a variable with linkage

[redi at gcc dot gnu dot org]

------- Comment #13 from redi at gcc dot gnu dot org  2010-01-12 01:00 -------
(In reply to comment #12)
> Comeau rejects it. Is this accepts-invalid, then?
> 

I think so, as I suggested in comment 3


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] use of a type with no linkage to declare a variable with linkage

[redi at gcc dot gnu dot org]

------- Comment #14 from redi at gcc dot gnu dot org  2010-01-12 01:08 -------
(In reply to comment #9)
> requires six posts from experts to explain.

I'm not sure where you got that number, after my second comment I was
correcting my own typos or your misunderstanding of unnamed namespaces :)


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] use of a type with no linkage to declare a variable with linkage

[igodard at pacbell dot net]

------- Comment #15 from igodard at pacbell dot net  2010-01-12 01:12 -------
Should I submit a second report so there is one for "accepts invalid" and a
different one for "diagnostic quality"?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] use of a type with no linkage to declare a variable with linkage

[manu at gcc dot gnu dot org]

------- Comment #16 from manu at gcc dot gnu dot org  2010-01-12 10:16 -------
(In reply to comment #15)
> Should I submit a second report so there is one for "accepts invalid" and a
> different one for "diagnostic quality"?
> 

No need, thanks. Both can be solved at the same time.


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |accepts-invalid


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] use of a type with no linkage to declare a variable with linkage

[jason at gcc dot gnu dot org]

------- Comment #17 from jason at gcc dot gnu dot org  2010-01-20 23:32 -------
We accept this testcase with a warning because it is both common and harmless.

In 4.5, this testcase will be accepted with no warning in -std=c++0x mode, as
we now implement DR 757.


-- 

jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jason at gcc dot gnu dot org
                   |dot org                     |
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2010-01-11 18:52:09         |2010-01-20 23:32:16
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] use of a type with no linkage to declare a variable with linkage

[jason at gcc dot gnu dot org]

------- Comment #18 from jason at gcc dot gnu dot org  2010-01-20 23:36 -------
So, removing the accepts-invalid keyword.  I'll fix the diagnostic in 4.6.


-- 

jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|accepts-invalid             |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] use of a type with no linkage to declare a variable with linkage

[jason at gcc dot gnu dot org]

------- Comment #19 from jason at gcc dot gnu dot org  2010-02-19 21:39 -------
Created an attachment (id=19925)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=19925&action=view)
patch for 4.6


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] use of a type with no linkage to declare a variable with linkage

[jason at gcc dot gnu dot org]

------- Comment #20 from jason at gcc dot gnu dot org  2010-04-07 15:54 -------
Subject: Bug 41970

Author: jason
Date: Wed Apr  7 15:54:17 2010
New Revision: 158071

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=158071
Log:
        PR c++/41970
        * decl.c (grokvardecl): Tweak warning message.
        (grokfndecl): Likewise.

Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/decl.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/g++.old-deja/g++.other/linkage1.C


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970

[Bug c++/41970] use of a type with no linkage to declare a variable with linkage

[jason at gcc dot gnu dot org]

------- Comment #21 from jason at gcc dot gnu dot org  2010-05-04 04:56 -------
Fixed for 4.6.


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jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.6.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41970