Proof of concept: Macros to manipulate %py3_shebang_flags

Currently, when packagers want to strip the -s flag,
they define %py3_shebang_flags to %nil or they %undefine it.

However, if we are to add more default flags in the future,
they will lose them all.

Instead, we now have %py3_shebang_flags_add and %py3_shebang_flags_remove
so packagers can explicitly remove the -s flag.

Intentionally, the old %py3_build macro keeps using the default.

macros.python

@@ -11,9 +11,45 @@
 %python_ext_suffix %(RPM_BUILD_ROOT= %{__python} -Esc "import sysconfig; print(sysconfig.get_config_var('EXT_SUFFIX'))")
 
 %py_setup setup.py
+
+# This is the "201x-era" macro, we also use it to define the default
 %py_shbang_opts -s
-%py_shbang_opts_nodash %(opts=%{py_shbang_opts}; echo ${opts#-})
-%py_shebang_flags %(opts=%{py_shbang_opts}; echo ${opts#-})
+
+# This is a convenient helper that strips the leading dash from %%py_shbang_opts
+%py_shbang_opts_nodash %{lua:print((rpm.expand('%?py_shbang_opts'):gsub('^%-', '')))}
+
+# Finally, this is the value everybody should actually use, with _add and _remove helpers
+%py_shebang_flags %{lua:
+-- py_shebang_flags is also a Lua global, so we can conveniently manipulate it repeatedly
+-- in the beginning however, it is not set, so we need to do it
+if py_shebang_flags == nil then
+    py_shebang_flags = rpm.expand('%?py_shbang_opts_nodash')
+end
+print(py_shebang_flags)
+}
+
+%py_shebang_flags_add() %{lua:
+if py_shebang_flags == nil then
+    py_shebang_flags = rpm.expand('%?py_shbang_opts_nodash')
+end
+for flag in rpm.expand('%?*'):gmatch('%a') do
+    index, _ = py_shebang_flags:find(flag)
+    if index == nil then
+        py_shebang_flags = py_shebang_flags .. flag
+    end
+end
+}
+
+%py_shebang_flags_remove() %{lua:
+if py_shebang_flags == nil then
+    py_shebang_flags = rpm.expand('%?py_shbang_opts_nodash')
+end
+for flag in rpm.expand('%?*'):gmatch('%a') do
+    py_shebang_flags, _ = py_shebang_flags:gsub(flag, '')
+end
+}
+
+
 %py_shebang_fix %{expand:\\\
   if [ -f /usr/bin/pathfix%{python_version}.py ]; then
     pathfix=/usr/bin/pathfix%{python_version}.py

macros.python3

@@ -9,9 +9,44 @@
 %python3_ext_suffix %(RPM_BUILD_ROOT= %{__python3} -Ic "import sysconfig; print(sysconfig.get_config_var('EXT_SUFFIX'))")
 %py3dir %{_builddir}/python3-%{name}-%{version}-%{release}
 
+# This is the "201x-era" macro, we also use it to define the default
 %py3_shbang_opts -s
-%py3_shbang_opts_nodash %(opts=%{py3_shbang_opts}; echo ${opts#-})
-%py3_shebang_flags %(opts=%{py3_shbang_opts}; echo ${opts#-})
+
+# This is a convenient helper that strips the leading dash from %%py3_shbang_opts
+%py3_shbang_opts_nodash %{lua:print((rpm.expand('%?py3_shbang_opts'):gsub('^%-', '')))}
+
+# Finally, this is the value everybody should actually use, with _add and _remove helpers
+%py3_shebang_flags %{lua:
+-- py3_shebang_flags is also a Lua global, so we can conveniently manipulate it repeatedly
+-- in the beginning however, it is not set, so we need to do it
+if py3_shebang_flags == nil then
+    py3_shebang_flags = rpm.expand('%?py3_shbang_opts_nodash')
+end
+print(py3_shebang_flags)
+}
+
+%py3_shebang_flags_add() %{lua:
+if py3_shebang_flags == nil then
+    py3_shebang_flags = rpm.expand('%?py3_shbang_opts_nodash')
+end
+for flag in rpm.expand('%?*'):gmatch('%a') do
+    index, _ = py3_shebang_flags:find(flag)
+    if index == nil then
+        py3_shebang_flags = py3_shebang_flags .. flag
+    end
+end
+}
+
+%py3_shebang_flags_remove() %{lua:
+if py3_shebang_flags == nil then
+    py3_shebang_flags = rpm.expand('%?py3_shbang_opts_nodash')
+end
+for flag in rpm.expand('%?*'):gmatch('%a') do
+    py3_shebang_flags, _ = py3_shebang_flags:gsub(flag, '')
+end
+}
+
+
 %py3_shebang_fix %{expand:\\\
   if [ -f /usr/bin/pathfix%{python3_version}.py ]; then
     pathfix=/usr/bin/pathfix%{python3_version}.py