Bug 1469861

See upstream bug here: https://github.com/powerline/powerline/issues/1800

Developer closed both bugs because it is apparently our fault for packaging the python version of the script as /usr/bin/powerline. 

See: 

F25:

file $(which powerline)
/usr/bin/powerline: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=04e4042f5650ff2b23f858862231a59472aeaddd, stripped

F26:

file $(which powerline)
/usr/bin/powerline: Python script, ASCII text executable

I suspect this unintentional and is some install time weirdness based on the way the developer decided to automatically choose which one would be build based on available dependencies, but I'll have to dive into the SPEC to say more. Get back when I can!

client/powerline.c: In function ‘main’:
client/powerline.c:125:36: warning: ‘__builtin___snprintf_chk’ output may be truncated before the last format character
  snprintf(num_args, NUM_ARGS_SIZE, "%x", argc - 1);
                                    ^~~~
In file included from /usr/include/stdio.h:939:0,
                 from client/powerline.c:4:
/usr/include/bits/stdio2.h:64:10: note: ‘__builtin___snprintf_chk’ output between 2 and 9 bytes into a destination of si
   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        __bos (__s), __fmt, __va_arg_pack ());
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/ccKwNdgL.o: In function `main':
/builddir/build/BUILD/powerline-2.6/client/powerline.c:114: undefined reference to `true_sun_len'
collect2: error: ld returned 1 exit status
ERROR:root:Command '['cc', '-O2', '-g', '-pipe', '-Wall', '-Werror=format-security', '-Wp,-D_FORTIFY_SOURCE=2', '-fexcep
Traceback (most recent call last):
  File "setup.py", line 38, in <module>
    compile_client()
  File "setup.py", line 35, in compile_client
    subprocess.check_call(compiler + shlex.split(cflags) + ['client/powerline.c', '-o', 'scripts/powerline'])
  File "/usr/lib64/python3.6/subprocess.py", line 291, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['cc', '-O2', '-g', '-pipe', '-Wall', '-Werror=format-security', '-Wp,-D_FORTIFY
Compiling C version of powerline-client failed
Using powerline.py script instead of C version



This is why F25 and F26 differ. 

It seems that you found that out the hard way given that as I'm looking at the SPEC differences between F25 and F26, you added this:

+# As we only have python files do not create a debuginfo package
+%global debug_package %{nil}

And switch it to the `noarch` BuildArch. 

The way the comment is written, with the absence of info about this in the changelog leads me to believe you didn't realize that this was an automatic fallback because the C program failed to build, so that's why I'm documenting that here. Again, more info happening at github, too.

powerline-2.6-2.fc26 has been submitted as an update to Fedora 26. https://bodhi.fedoraproject.org/updates/FEDORA-2017-222bbba94a

powerline-2.6-2.fc26 has been pushed to the Fedora 26 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2017-222bbba94a

powerline-2.6-2.fc26 has been pushed to the Fedora 26 stable repository. If problems still persist, please make note of it in this bug report.