New opt-in possibility to fix byte-compilation reproducibility

A new script brp-fix-pyc-reproducibility creates an opt-in way of how to fix
problems with the reproducibility of byte-compiled Python files. The script
uses marshalparser [0] which currently doesn't provide solutions for all issues
but can fix at least problems with reference flags. For more info see
this Bugzilla [1].

If you want to use this new feature, you need to define
`%py_reproducible_pyc_path` to specify a path you want to fix `.pyc`
files in (recursively) and build-require /usr/bin/marshalparser.

if you forget to build-require the parser. The error message is:
```
+ /usr/lib/rpm/redhat/brp-python-bytecompile '' 1 0
Bytecompiling .py files below /builddir/build/BUILDROOT/tldr-0.5-2.fc33.x86_64/usr/lib/python3.9 using /usr/bin/python3.9
+ /usr/lib/rpm/redhat/brp-fix-pyc-reproducibility /builddir/build/BUILDROOT/tldr-0.5-2.fc33.x86_64
ERROR: If %py_reproducible_pyc_path is defined, you have to also BuildRequire: /usr/bin/marshalparser !
error: Bad exit status from /var/tmp/rpm-tmp.UUJr4v (%install)
```

A build fails if the parser is not able to parse any of the `.pyc` files.

And finally, if a build is properly configured it produces fixed `.pyc` files.

Currently, `.pyc` files in the tldr package contain a lot of unused reference flags:
```
$ dnf install -y tldr
$ marshalparser --unused /usr/lib/python3.9/site-packages/__pycache__/tldr.cpython-39.pyc
… long output …
190 - Flag_ref(byte=9610, type='TYPE_SHORT_ASCII_INTERNED', content=b'init', usages=0)
191 - Flag_ref(byte=9633, type='TYPE_SHORT_ASCII_INTERNED', content=b'source', usages=0)
192 - Flag_ref(byte=9651, type='TYPE_SHORT_ASCII_INTERNED', content=b'argv', usages=0)
193 - Flag_ref(byte=9657, type='TYPE_SHORT_ASCII_INTERNED', content=b'print_help', usages=0)
194 - Flag_ref(byte=9669, type='TYPE_SHORT_ASCII_INTERNED', content=b'stderr', usages=0)
195 - Flag_ref(byte=9682, type='TYPE_SHORT_ASCII_INTERNED', content=b'parse_args', usages=0)
196 - Flag_ref(byte=9737, type='TYPE_SHORT_ASCII_INTERNED', content=b'encode', usages=0)
197 - Flag_ref(byte=9782, type='TYPE_SHORT_ASCII_INTERNED', content=b'parser', usages=0)
198 - Flag_ref(byte=9790, type='TYPE_SHORT_ASCII_INTERNED', content=b'options', usages=0)
199 - Flag_ref(byte=9799, type='TYPE_SHORT_ASCII_INTERNED', content=b'rest', usages=0)
200 - Flag_ref(byte=9821, type='TYPE_SHORT_ASCII_INTERNED', content=b'result', usages=0)
202 - Flag_ref(byte=10022, type='TYPE_SHORT_ASCII_INTERNED', content=b'__main__', usages=0)
203 - Flag_ref(byte=10102, type='TYPE_SHORT_ASCII_INTERNED', content=b'argparse', usages=0)
204 - Flag_ref(byte=10433, type='TYPE_SHORT_ASCII_INTERNED', content=b'__name__', usages=0)
205 - Flag_ref(byte=10463, type='TYPE_SHORT_ASCII_INTERNED', content=b'<module>', usages=0)
```

This new feature fixes them:

```
$ marshalparser --unused /usr/lib/python3.9/site-packages/__pycache__/tldr.cpython-39.pyc
<empty output>
```

[0] https://github.com/fedora-python/marshalparser
[1] https://bugzilla.redhat.com/show_bug.cgi?id=1686078

brp-fix-pyc-reproducibility

@@ -0,0 +1,18 @@
+#!/bin/bash -e
+
+# If using normal root, avoid changing anything.
+if [ -z "$RPM_BUILD_ROOT" -o "$RPM_BUILD_ROOT" = "/" ]; then
+  exit 0
+fi
+
+# Defined as %py_reproducible_pyc_path macro and passed here as
+# the first command-line argument
+path_to_fix=$1
+
+# First, check that the parser is available:
+if [ ! -x /usr/bin/marshalparser ]; then
+  echo "ERROR: If %py_reproducible_pyc_path is defined, you have to also BuildRequire: /usr/bin/marshalparser !"
+  exit 1
+fi
+
+find "$path_to_fix" -type f -name "*.pyc" | xargs /usr/bin/marshalparser --fix --overwrite

macros

@@ -233,6 +233,7 @@ print(result)
 %__brp_strip_comment_note /usr/lib/rpm/brp-strip-comment-note %{__strip} %{__objdump}
 %__brp_strip_static_archive /usr/lib/rpm/brp-strip-static-archive %{__strip}
 %__brp_python_bytecompile /usr/lib/rpm/redhat/brp-python-bytecompile "" "%{?_python_bytecompile_errors_terminate_build}" "%{?_python_bytecompile_extra}"
+%__brp_fix_pyc_reproducibility /usr/lib/rpm/redhat/brp-fix-pyc-reproducibility
 %__brp_python_hardlink /usr/lib/rpm/brp-python-hardlink
 # __brp_mangle_shebangs_exclude - shebangs to exclude
 # __brp_mangle_shebangs_exclude_file - file from which to get shebangs to exclude
@@ -250,6 +251,7 @@ print(result)
     %{?__brp_strip_lto} \
     %{?__brp_strip_static_archive} \
     %{?py_auto_byte_compile:%{?__brp_python_bytecompile}} \
+    %{?py_reproducible_pyc_path:%{?__brp_fix_pyc_reproducibility} "%{py_reproducible_pyc_path}"} \
     %{?__brp_python_hardlink} \
     %{?__brp_mangle_shebangs} \
 %{nil}

redhat-rpm-config.spec

@@ -6,8 +6,8 @@
 
 Summary: Red Hat specific rpm configuration files
 Name: redhat-rpm-config
-Version: 161
-Release: 2%{?dist}
+Version: 162
+Release: 1%{?dist}
 # No version specified.
 License: GPL+
 URL: https://src.fedoraproject.org/rpms/redhat-rpm-config
@@ -53,6 +53,10 @@ Source201: brp-mangle-shebangs
 # however, now we can do Fedora changes within
 Source202: brp-python-bytecompile
 
+# for fixing pyc files reproducibility with marshalparser
+# https://github.com/fedora-python/marshalparser
+Source203: brp-fix-pyc-reproducibility
+
 # Dependency generator scripts (deprecated)
 Source300: find-provides
 Source301: find-provides.ksyms
@@ -207,6 +211,9 @@ install -p -m 644 -t %{buildroot}%{_rpmluadir}/fedora/srpm forge.lua
 %{_rpmconfigdir}/macros.d/macros.kmp
 
 %changelog
+* Thu Jul 16 2020 Lumír Balhar <lbalhar@redhat.com> - 162-1
+- New script brp-fix-pyc-reproducibility
+
 * Tue Jun 16 2020 Lumír Balhar <lbalhar@redhat.com> - 161-2
 - Use stdlib compileall for Python >= 3.9