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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/93503] [9/10/11/12 Regression] Duplicated warning on pure
 virtual template
Date: Fri, 07 Jan 2022 01:44:16 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D93503

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
For the reduced testcase this is what clang produces:
<source>:3:5: error: 'virtual' cannot be specified on member function templ=
ates
    virtual int foo(int) =3D 0;
    ^~~~~~~~
<source>:3:17: error: illegal initializer (only variables can be initialize=
d)
    virtual int foo(int) =3D 0;
                ^

MSVC:

<source>(3): error C2898: 'int S::foo(int)': member function templates cann=
ot
be virtual
<source>(3): error C2187: syntax error: 'constant' was unexpected here
<source>(3): note: This diagnostic occurred in the compiler generated funct=
ion
'int S::foo(int)'

ICC:
<source>(3): error: "virtual" is not allowed in a function template declara=
tion
      virtual int foo(int) =3D 0;
      ^

<source>(3): error: expected a ";"
      virtual int foo(int) =3D 0;
                           ^



Clang's error message is incorrect even because it says only variables can =
be
initialized which is not true as virtual functions can be initilized to 0 s=
o it
can be considered a pure virtual.
Maybe GCC's second error message could be changed to talk about pure virtual
and such.=