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* [Bug c++/66472] New: -Wshadow gets confused by using statements in template classes
@ 2015-06-09 11:25 gael.guennebaud at gmail dot com
2015-06-09 12:39 ` [Bug c++/66472] " chtz at informatik dot uni-bremen.de
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: gael.guennebaud at gmail dot com @ 2015-06-09 11:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66472
Bug ID: 66472
Summary: -Wshadow gets confused by using statements in template
classes
Product: gcc
Version: 5.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: gael.guennebaud at gmail dot com
Target Milestone: ---
This is a followup to bug 57709 that disabled shadow warnings between variables
and class functions. However, -Wshadow still trigger false positive when a base
member functions is imported with the "using" keyword, as in the following
example (tested with gcc 5.1):
template<typename T> struct BaseClass {
BaseClass(int size) : m_size(size) {}
int size() { return m_size; }
int m_size;
};
template<typename T> struct Foo : BaseClass<T> {
typedef BaseClass<T> Base;
Foo(int size) : Base(size) {}
using Base::size;
};
$ g++-mp-5 gcc_shadow.cpp -c -Wshadow
gcc_shadow.cpp: In constructor 'Foo<T>::Foo(int)':
gcc_shadow.cpp:9:17: warning: declaration of 'size' shadows a member of
'Foo<T>' [-Wshadow]
Foo(int size) : Base(size) {}
^
gcc_shadow.cpp:10:15: note: shadowed declaration is here
using Base::size;
Note that clang does not warn in this case, so it should be possible to figure
out that in this case, the imported "size" symbol is a function and not a
variable.
As suggested there https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57709#c16, I
tried to break at the call to warning_at to give you more input, but with no
luck, as if warning_at was not called at all. (I also tried to break at any
*warning* symbol with same result).
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/66472] -Wshadow gets confused by using statements in template classes
2015-06-09 11:25 [Bug c++/66472] New: -Wshadow gets confused by using statements in template classes gael.guennebaud at gmail dot com
@ 2015-06-09 12:39 ` chtz at informatik dot uni-bremen.de
2015-06-09 12:54 ` gael.guennebaud at gmail dot com
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: chtz at informatik dot uni-bremen.de @ 2015-06-09 12:39 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66472
Christoph Hertzberg <chtz at informatik dot uni-bremen.de> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |chtz at informatik dot uni-bremen.
| |de
--- Comment #1 from Christoph Hertzberg <chtz at informatik dot uni-bremen.de> ---
Wouldn't this actually be a valid warning if BaseClass had a constructor taking
a function pointer/member function pointer?
struct BaseClass {
BaseClass(int) { std::cout << "int\n"; }
BaseClass(int () ) { std::cout << "int()\n"; }
BaseClass(int (BaseClass::*)()) {std::cout << "int (BaseClass::*)()\n"; }
static int size() { return 0;}
int size2() { return 0; }
};
struct Foo : public BaseClass {
using BaseClass::size;
using BaseClass::size2;
// size shadows BaseClass::size!
Foo(int size) : BaseClass(size) {}
Foo() : BaseClass(size) {} // uses BaseClass::size
Foo(char) : BaseClass(size2) {} // uses BaseClass::size2
};
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/66472] -Wshadow gets confused by using statements in template classes
2015-06-09 11:25 [Bug c++/66472] New: -Wshadow gets confused by using statements in template classes gael.guennebaud at gmail dot com
2015-06-09 12:39 ` [Bug c++/66472] " chtz at informatik dot uni-bremen.de
@ 2015-06-09 12:54 ` gael.guennebaud at gmail dot com
2015-06-09 13:07 ` glisse at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: gael.guennebaud at gmail dot com @ 2015-06-09 12:54 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66472
--- Comment #2 from Gael Guennebaud <gael.guennebaud at gmail dot com> ---
But with the same reasoning you would end up reintroducing shadow warnings
between local variables and *any* functions, not only the ones visible from a
using statement. It has been recognized that triggering a warning in such a
case was too much:
- gcc 4.8 removed them for free functions
- gcc 5.0 removed them for member functions
and I think that it thus make sense to remove them for member functions visible
through "using". Did I miss something special regarding the use of "using"?
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/66472] -Wshadow gets confused by using statements in template classes
2015-06-09 11:25 [Bug c++/66472] New: -Wshadow gets confused by using statements in template classes gael.guennebaud at gmail dot com
2015-06-09 12:39 ` [Bug c++/66472] " chtz at informatik dot uni-bremen.de
2015-06-09 12:54 ` gael.guennebaud at gmail dot com
@ 2015-06-09 13:07 ` glisse at gcc dot gnu.org
2015-06-09 13:11 ` manu at gcc dot gnu.org
2021-12-25 1:43 ` pinskia at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: glisse at gcc dot gnu.org @ 2015-06-09 13:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66472
--- Comment #3 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to Gael Guennebaud from comment #0)
> As suggested there https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57709#c16, I
> tried to break at the call to warning_at to give you more input, but with no
> luck, as if warning_at was not called at all. (I also tried to break at any
> *warning* symbol with same result).
I compile with g++ -wrapper gdb,--args ... where this gcc was compile with -O0
-g. Breaking on warning_at shows that member is a using_decl.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/66472] -Wshadow gets confused by using statements in template classes
2015-06-09 11:25 [Bug c++/66472] New: -Wshadow gets confused by using statements in template classes gael.guennebaud at gmail dot com
` (2 preceding siblings ...)
2015-06-09 13:07 ` glisse at gcc dot gnu.org
@ 2015-06-09 13:11 ` manu at gcc dot gnu.org
2021-12-25 1:43 ` pinskia at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: manu at gcc dot gnu.org @ 2015-06-09 13:11 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66472
Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |manu at gcc dot gnu.org
--- Comment #4 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
> As suggested there https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57709#c16, I
> tried to break at the call to warning_at to give you more input, but with no
> luck, as if warning_at was not called at all. (I also tried to break at any
> *warning* symbol with same result).
Probably because you are debugging the driver instead of the compiler proper:
https://gcc.gnu.org/wiki/DebuggingGCC
Sorry, I should have mentioned that.
>From gcc-bugs-return-488483-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Tue Jun 09 13:15:23 2015
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From: "manu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/66472] -Wshadow gets confused by using statements in template classes
Date: Tue, 09 Jun 2015 13:15:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66472
--- Comment #5 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Marc Glisse from comment #3)
> I compile with g++ -wrapper gdb,--args ... where this gcc was compile with
> -O0 -g. Breaking on warning_at shows that member is a using_decl.
Is there anyway to tell what the using_decl is actually representing? Perhaps
via its type?
I think this is one of those cases where false negatives are more annoying than
false positives are dangerous, thus maybe the warning should be silent for all
using_decl.
>From gcc-bugs-return-488484-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Tue Jun 09 13:15:58 2015
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From: "chtz at informatik dot uni-bremen.de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/66472] -Wshadow gets confused by using statements in template classes
Date: Tue, 09 Jun 2015 13:15:00 -0000
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--- Comment #6 from Christoph Hertzberg <chtz at informatik dot uni-bremen.de> ---
Ok, good point on shadowing free functions.
Next pathological example: If you have a template specialization of your Base
with a static member variable called `size`, wouldn't the warning make sense?
template <class T>
struct Base {
Base(int y) {std::cout << "y=" <<y <<"\n";}
T size();
};
template<class T>
struct Bar : Base<T> {
using Base<T>::size;
Bar(int size) : Base<T>(size) {}
Bar() : Base<T>(size) {} // only works for T==int
};
// Specialization, probably not visible when Bar is defined:
template<>
struct Base<int> {
Base<int>(int x) {std::cout << "x=" <<x <<"\n";}
const static int sizeB;
};
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/66472] -Wshadow gets confused by using statements in template classes
2015-06-09 11:25 [Bug c++/66472] New: -Wshadow gets confused by using statements in template classes gael.guennebaud at gmail dot com
` (3 preceding siblings ...)
2015-06-09 13:11 ` manu at gcc dot gnu.org
@ 2021-12-25 1:43 ` pinskia at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-12-25 1:43 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66472
--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
GCC even warns for:
template<typename T> struct Foo : T {
typedef T Base;
Foo(int size) : Base(size) {}
using Base::size;
};
While clang does not even warn for this case:
struct Foo {
Foo(int size) {}
int size;
};
clang does not warn for constructors but do for normal methods:
struct Foo {
void g(int size) {}
int size;
};
I don't know if it is a good idea to warn for constructors after all ....
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-12-25 1:43 UTC | newest]
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2015-06-09 11:25 [Bug c++/66472] New: -Wshadow gets confused by using statements in template classes gael.guennebaud at gmail dot com
2015-06-09 12:39 ` [Bug c++/66472] " chtz at informatik dot uni-bremen.de
2015-06-09 12:54 ` gael.guennebaud at gmail dot com
2015-06-09 13:07 ` glisse at gcc dot gnu.org
2015-06-09 13:11 ` manu at gcc dot gnu.org
2021-12-25 1:43 ` pinskia at gcc dot gnu.org
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