fix(build): change resolve_requires to be independent of pip

Fixes: #451

setup.py

@@ -1,6 +1,6 @@
 #!/usr/bin/env python
 #
-# Copyright 2015-2023 Flavio Garcia
+# Copyright 2015-2024 Flavio Garcia
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -16,35 +16,30 @@
 
 import firenado
 from setuptools import setup, find_packages
-import sys
+import os
 
-try:
-    # for pip >= 10
-    from pip._internal.req import parse_requirements
-except ImportError:
-    # for pip <= 9.0.3
-    print("error: Upgrade to a pip version newer than 10. Run \"pip install "
-          "--upgrade pip\".")
-    sys.exit(1)
+with open("README.md", "r") as fh:
+    long_description = fh.read()
 
 
 # Solution from http://bit.ly/29Yl8VN
 def resolve_requires(requirements_file):
-    try:
-        requirements = parse_requirements("./%s" % requirements_file,
-                                          session=False)
-        return [str(ir.req) for ir in requirements]
-    except AttributeError:
-        # for pip >= 20.1.x
-        # Need to run again as the first run was ruined by the exception
-        requirements = parse_requirements("./%s" % requirements_file,
-                                          session=False)
-        # pr stands for parsed_requirement
-        return [str(pr.requirement) for pr in requirements]
-
+    requires = []
+    if os.path.isfile(f"./{requirements_file}"):
+        file_dir = os.path.dirname(f"./{requirements_file}")
+        with open(f"./{requirements_file}") as f:
+            for raw_line in f.readlines():
+                line = raw_line.strip().replace("\n", "")
+                if len(line) > 0:
+                    if line.startswith("-r "):
+                        partial_file = os.path.join(file_dir, line.replace(
+                            "-r ", ""))
+                        partial_requires = resolve_requires(partial_file)
+                        requires = requires + partial_requires
+                        continue
+                    requires.append(line)
+    return requires
 
-with open("README.md", "r") as fh:
-    long_description = fh.read()
 
 setup(
     name="Firenado",