[This bug is NOT targeted to the upcoming trixie release]

Please keep this issue open in the bug tracker for the package it
was filed for.  If a fix in another package is required, please
file a bug for the other package (or clone), and add a block in this
package. Please keep the issue open until the package can be built in
a follow-up test rebuild.

The package fails to build in a test rebuild on at least amd64 with
gcc-15/g++-15, but succeeds to build with gcc-14/g++-14. The
severity of this report will be raised before the forky release.

The full build log can be found at:
http://qa-logs.debian.net/2025/02/16/amd64exp/kakasi_2.3.6-4.2_unstable_gccexp.log.gz
The last lines of the build log are at the end of this report.

To build with GCC 15, either set CC=gcc-15 CXX=g++-15 explicitly,
or install the gcc, g++, gfortran, ... packages from experimental.

  apt-get -t=experimental install g++

GCC 15 now defaults to the C23/C++23 standards, exposing many FTBFS.
Other Common build failures are new warnings resulting in build failures
with -Werror turned on, or new/dropped symbols in Debian symbols files.
For other C/C++ related build failures see the porting guide at
http://gcc.gnu.org/gcc-15/porting_to.html

[...]
hh2.c: In function ‘H2a’:
hh2.c:677:1: warning: old-style function definition [-Wold-style-definition]
  677 | H2a(c, n)
      | ^~~
k2.c: In function ‘k2j’:
hh2.c: In function ‘H2j’:
k2.c:495:1: warning: old-style function definition [-Wold-style-definition]
  495 | k2j(c, n)
      | ^~~
hh2.c:685:1: warning: old-style function definition [-Wold-style-definition]
  685 | H2j(c, n)
      | ^~~
k2.c: In function ‘k2K’:
k2.c:503:1: warning: old-style function definition [-Wold-style-definition]
  503 | k2K(c, n)
      | ^~~
hh2.c: In function ‘H2K’:
hh2.c:693:1: warning: old-style function definition [-Wold-style-definition]
  693 | H2K(c, n)
      | ^~~
make[4]: *** [Makefile:438: kakasi.o] Error 1
hh2.c: In function ‘H2k’:
hh2.c:741:1: warning: old-style function definition [-Wold-style-definition]
  741 | H2k(c, n)
      | ^~~
k2.c: In function ‘k2H’:
k2.c:571:1: warning: old-style function definition [-Wold-style-definition]
  571 | k2H(c, n)
      | ^~~
hh2.c: In function ‘H2H’:
hh2.c:793:1: warning: old-style function definition [-Wold-style-definition]
  793 | H2H(c, n)
      | ^~~
hh2.c:851:1: warning: control reaches end of non-void function [-Wreturn-type]
  851 | }
      | ^
kk2.c: In function ‘K2rom’:
kk2.c:582:1: warning: old-style function definition [-Wold-style-definition]
  582 | K2rom(c, n, type)
      | ^~~~~
kk2.c: In function ‘K2a’:
kk2.c:684:1: warning: old-style function definition [-Wold-style-definition]
  684 | K2a(c, n)
      | ^~~
kk2.c: In function ‘K2j’:
kk2.c:692:1: warning: old-style function definition [-Wold-style-definition]
  692 | K2j(c, n)
      | ^~~
kk2.c: In function ‘K2H’:
kk2.c:700:1: warning: old-style function definition [-Wold-style-definition]
  700 | K2H(c, n)
      | ^~~
kk2.c: In function ‘K2k’:
kk2.c:767:1: warning: old-style function definition [-Wold-style-definition]
  767 | K2k(c, n)
      | ^~~
kk2.c: In function ‘K2K’:
kk2.c:818:1: warning: old-style function definition [-Wold-style-definition]
  818 | K2K(c, n)
      | ^~~
make[4]: Leaving directory '/build/reproducible-path/kakasi-2.3.6/src'
make[3]: *** [Makefile:507: all-recursive] Error 1
make[3]: Leaving directory '/build/reproducible-path/kakasi-2.3.6'
make[2]: *** [Makefile:379: all] Error 2
make[2]: Leaving directory '/build/reproducible-path/kakasi-2.3.6'
dh_auto_build: error: make -j8 returned exit code 2
make[1]: *** [debian/rules:18: override_dh_auto_build] Error 25
make[1]: Leaving directory '/build/reproducible-path/kakasi-2.3.6'
make: *** [debian/rules:12: binary] Error 2
dpkg-buildpackage: error: debian/rules binary subprocess returned exit status 2