[LLVMbugs] [Bug 16792] New: Redeclaration of nested type misdiagosed as forward-decl

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=16792

            Bug ID: 16792
           Summary: Redeclaration of nested type misdiagosed as
                    forward-decl
           Product: clang
           Version: 3.3
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++11
          Assignee: unassignedclangbugs at nondot.org
          Reporter: imkinghan at gmail.com
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Compiling the following C++11 program (`-Wall -std=c++11`):

// main.cpp
struct X
{
    struct Y {};
};

struct X::Y xy; /*B*/
struct X::Y; /*A*/

int main()
{
    return 0;
}
// EOF


clang 3.3 diagnoses line /*A*/:

`error: forward declaration of struct cannot have a nested name specifier`

I don't believe there is an error there. The line is correctly parsed as a 
`simple-declaration` of `struct X::Y` the form 

`decl-specifier-seq[opt] init-declarator-list[opt];`

in which the `decl-specifier-seq` is present and the `init-declarator-list`
is absent. But it is not a forward declaration because `X::Y` is aleady
defined. And clang considers it already defined, because it finds 
no fault with the previous line /*B*/.

G++ 4.8.1, diagnoses /*A*/:

`warning: declaration ‘struct X::Y’ does not declare anything`

which I take to mean that nothing of the defined type `X::Y` is declared.

Similarly Intel C++ 13.1.3. MSVC++ 120 (`/Wall`) has nothing to say of the
line.

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