[Bug c++/58263] New: [feature request] friend class $UndefinedClass

[Bug c++/58263] New: [feature request] friend class $UndefinedClass

[vova7890 at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58263

            Bug ID: 58263
           Summary: [feature request] friend class $UndefinedClass
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: trivial
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vova7890 at mail dot ru

Idea is in:

class MyClass1
{
   friend class MyClas2; // trivial stupid human issue with MyClas2 -> MyClass2
private:
   void help();
};


class MyClass2
{
public:
   void need(MyClass1 *cl) {
      cl->help();   // error: is private!!
   }
};


Maybe need to check, have we declaration or not. If not - got a warning about
missing declaration.

[Bug c++/58263] [feature request] friend class $UndefinedClass

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58263

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|trivial                     |enhancement

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to vova7890 from comment #0)
> Maybe need to check, have we declaration or not. If not - got a warning
> about missing declaration.

That can't work, consider:

// A.h
class A {
  A();
  friend class B;
};

// B.h
#include "A.h"
class B { };

// A.cc
#include "A.h"
A::A() {}

Do we warn in A.cc that B is not defined? It is defined in another header, but
that isn't included by A.cc because it isn't needed.

[Bug c++/58263] [feature request] friend class $UndefinedClass

[vova7890 at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58263

--- Comment #2 from vova7890 <vova7890 at mail dot ru> ---
(In reply to Jonathan Wakely from comment #1)
> Do we warn in A.cc that B is not defined? It is defined in another header,
> but that isn't included by A.cc because it isn't needed.



We warn about implicit friend class MyClas2. For example, we wrong writed class
name(as in example MyClas2 -> MyClass2, missed the letter "s" in the word
Class), try to compile that and see:

[vova7890@localhost tmp]$ g++ -O2 main.cpp
main.cpp: In member function 'void MyClass2::need(MyClass1*)':
main.cpp:10:9: error: 'void MyClass1::help()' is private
    void help();
         ^
main.cpp:18:16: error: within this context
       cl->help();   // error: is private!!


But, we don`t understand why it`s private, because we think that we correctly
writed class name(friend class MyClass2), and do not see where is the bug
exactly. But, if compiler say as, about implicit friend class MyClas2, like
this:

[vova7890@localhost tmp]$ g++ -O2 main.cpp
main.cpp:8:12: warning: implicit declaration of friend 'MyClas2'
    friend class MyClas2;
                 ^
main.cpp: In member function 'void MyClass2::need(MyClass1*)':
main.cpp:10:9: error: 'void MyClass1::help()' is private
    void help();
         ^
main.cpp:18:16: error: within this context
       cl->help();   // error: is private!!


we see where is exactly issue, and just correct that stupid typo.

[Bug c++/58263] [feature request] friend class $UndefinedClass

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58263

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
But that will warn about valid code, where you didn't spell the name wrong.

[Bug c++/58263] [feature request] friend class $UndefinedClass

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58263

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
How about looking into the MyClass1 to see if there is a friend class and have
a quick heuristic about the spelling mistake when doing the error message?

[Bug c++/58263] [feature request] friend class $UndefinedClass

[vova7890 at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58263

--- Comment #5 from vova7890 <vova7890 at mail dot ru> ---
(In reply to Jonathan Wakely from comment #3)
> But that will warn about valid code, where you didn't spell the name wrong.

Yes, but it can be not in one file, as in example. If it in one file, and
friend class is below the main class, can avoid warning by this:

class MyClass2;

class MyClass1
{
   friend class MyClass2; // trivial stupid human issue with MyClas2 ->
MyClass2
private:
   void help();
};

class MyClass2
{
public:
   void need(MyClass1 *cl) {
      cl->help();   // error: is private!!
   }
};

Also, maybe can use it on paranoid level warnings, for example.

[Bug c++/58263] [feature request] friend class $UndefinedClass

[vova7890 at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58263

--- Comment #6 from vova7890 <vova7890 at mail dot ru> ---
(In reply to Andrew Pinski from comment #4)
> How about looking into the MyClass1 to see if there is a friend class and
> have a quick heuristic about the spelling mistake when doing the error
> message?

Good idea. Can lookup for class name in visible fields, and also in curent
source, including fields after friend-contained class.