[Bug c++/105511] New: Spurious warning: "expected 'template' keyword..." when lt and gt compare over ternary

[Bug c++/105511] New: Spurious warning: "expected 'template' keyword..." when lt and gt compare over ternary

[cuzdav at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105511

            Bug ID: 105511
           Summary: Spurious warning: "expected 'template' keyword..."
                    when lt and gt compare over ternary
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: cuzdav at gmail dot com
  Target Milestone: ---

Only on g++ 12 (new warning).

Building with the freshly released G++12 with warning enabled
(-Werror=missing-template-keyword)

Complete, minimized code:

template <typename X>
bool before(bool ascending, X & a, X * b) {
    return ascending ? a.value < (*b).value : a.value > (*b).value;
}


<source>:4:26: warning: expected 'template' keyword before dependent template
name [-Wmissing-template-keyword]
    4 |     return ascending ? a.value < (*b).value : a.value > (*b).value;
      |                          ^~~~~

Visible on Compiler Explorer
https://godbolt.org/z/dW9hjbdex

Yes, the left-angle and right-angle brackets are present, but it's not looking
quite hard enough to see that they are on opposite sides of a ternary ':'.


My Compiler, if it matters:
/opt/imc/gcc-12.1.0/bin/g++
(base) bash-4.2$ g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/opt/imc/gcc-12.1.0/libexec/gcc/x86_64-pc-linux-gnu/12.1.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-12.1.0/configure --prefix=/opt/imc/gcc-12.1.0
--enable-languages=c,c++,fortran,lto --disable-multilib
--with-build-time-tools=/home/trading/cuzdav/code/imc-gcc/gcc/12.1.0/INSTALLDIR//opt/imc/gcc-12.1.0/bin
--enable-libstdcxx-time=rt
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.1.0 (GCC)

[Bug c++/105511] [12/13 Regression] Spurious warning: "expected 'template' keyword..." when lt and gt compare over ternary

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105511

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
      Known to work|                            |11.1.0, 11.3.0
            Summary|Spurious warning: "expected |[12/13 Regression] Spurious
                   |'template' keyword..." when |warning: "expected
                   |lt and gt compare over      |'template' keyword..." when
                   |ternary                     |lt and gt compare over
                   |                            |ternary
      Known to fail|                            |12.1.0
   Target Milestone|---                         |12.3
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2022-10-31

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

r12-6563-gb8ffa71e4271ae introduced the warning and enabled it by default.
I say this is a regression since the warning is enabled by default and I can't
even see how to avoid the warning.

[Bug c++/105511] [12/13 Regression] Spurious warning: "expected 'template' keyword..." when lt and gt compare over ternary

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105511

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
I'm not sure if there's anything to fix; the manual says:

In rare cases it is possible to get false positives. To silence this, wrap
the expression in parentheses. For example, the following is treated as a
template, even where m and N are integers:

@smallexample
void NotATemplate (my_class t)
@{
  int N = 5;

  bool test = t.m < N > (0); // Treated as a template.
  test = (t.m < N) > (0); // Same meaning, but not treated as a template.
@}
@end smallexample

so

return ascending ? (a.value < (*b).value) : a.value > (*b).value;

prevents the warning.

[Bug c++/105511] [12/13 Regression] Spurious warning: "expected 'template' keyword..." when lt and gt compare over ternary

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105511

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |WONTFIX

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
So indeed it works as documented, thus WONTFIX.