Add common Lua functions, use a Lua function in %python_provide

python.lua

@@ -0,0 +1,32 @@
+-- Convenience Lua functions that can be used within Python srpm/rpm macros
+
+-- Determine alternate names provided from the given name.
+-- Used in pythonname provides generator, python_provide and py_provides.
+-- There are 2 rules:
+--  python3-foo  -> python-foo, python3X-foo
+--  python3X-foo -> python-foo, python3-foo
+-- There is no python-foo -> rule, python-foo packages are version agnostic.
+-- Returns a table/array with strings. Empty when no rule matched.
+local function python_altnames(name)
+  local xy = rpm.expand('%{__default_python3_pkgversion}')
+  local altnames = {}
+  local replaced
+  -- NB: dash needs to be escaped!
+  if name:match('^python3%-') then
+    for i, prefix in ipairs({'python-', 'python' .. xy .. '-'}) do
+      replaced = name:gsub('^python3%-', prefix)
+      table.insert(altnames, replaced)
+    end
+  elseif name:match('^python' .. xy .. '%-') then
+    for i, prefix in ipairs({'python-', 'python3-'}) do
+      replaced = name:gsub('^python' .. xy .. '%-', prefix)
+      table.insert(altnames, replaced)
+    end
+  end
+  return altnames
+end
+
+
+return {
+  python_altnames = python_altnames,
+}