fix: change the pip runner string based on a pip version check

- if pip version is less than 19.3, choose to run main directly as its a
  function, whereas with pip versions starting with 19.3, execute the
  function `main` inside the pip.main module

Author: sriram-mv

aws_lambda_builders/workflows/python_pip/compat.py

@@ -21,6 +21,23 @@ def pip_import_string(python_exe):
         return 'from pip._internal import main'
 
 
+def pip_runner_string(python_exe):
+    os_utils = OSUtils()
+    cmd = [
+        python_exe,
+        "-c",
+        "import pip; assert (int(pip.__version__.split('.')[0]) <= 19 and int(pip.__version__.split('.')[1]) < 3)"
+    ]
+    p = os_utils.popen(cmd, stdout=os_utils.pipe, stderr=os_utils.pipe)
+    p.communicate()
+    # Pip changed main to be a module instead of a function from 19.3
+    # and added a separate main function within the main module.
+    if p.returncode == 0:
+        return 'import sys; %s; sys.exit(main(%s))'
+    else:
+        return 'import sys; %s; sys.exit(main.main(%s))'
+
+
 if os.name == 'nt':
     # windows
     # This is the actual patch used on windows to prevent distutils from

aws_lambda_builders/workflows/python_pip/packager.py

@@ -9,7 +9,7 @@
 from email.parser import FeedParser
 
 
-from .compat import pip_import_string
+from .compat import pip_import_string, pip_runner_string
 from .compat import pip_no_compile_c_env_vars
 from .compat import pip_no_compile_c_shim
 from .utils import OSUtils
@@ -553,6 +553,7 @@ def __init__(self, osutils=None, python_exe=None, import_string=None):
         self.python_exe = python_exe
         if import_string is None:
             import_string = pip_import_string(python_exe=self.python_exe)
+        self.run_pip_string = pip_runner_string(python_exe=self.python_exe)
         self._import_string = import_string
 
     def main(self, args, env_vars=None, shim=None):
@@ -561,7 +562,7 @@ def main(self, args, env_vars=None, shim=None):
         if shim is None:
             shim = ''
         run_pip = (
-            'import sys; %s; sys.exit(main(%s))'
+            self.run_pip_string
         ) % (self._import_string, args)
         exec_string = '%s%s' % (shim, run_pip)
         invoke_pip = [self.python_exe, '-c', exec_string]

tests/unit/workflows/python_pip/test_packager.py

@@ -1,5 +1,6 @@
 import sys
 from collections import namedtuple
+from unittest import TestCase
 
 import mock
 import pytest
@@ -70,7 +71,7 @@ def osutils():
 
 class FakePopen(object):
     def __init__(self, rc, out, err):
-        self.returncode = 0
+        self.returncode = rc
         self._out = out
         self._err = err
 
@@ -303,14 +304,24 @@ def test_inject_unknown_error_if_no_stderr(self, pip_factory):
         assert str(einfo.value) == 'Unknown error'
 
 
-class TestSubprocessPip(object):
+class TestSubprocessPip(TestCase):
     def test_does_use_custom_pip_import_string(self):
         fake_osutils = FakePopenOSUtils([FakePopen(0, '', '')])
         expected_import_statement = 'foobarbaz'
         pip = SubprocessPip(osutils=fake_osutils,
-                            import_string=expected_import_statement)
+                            import_string=expected_import_statement,
+                            python_exe=sys.executable)
         pip.main(['--version'])
 
         pip_execution_string = fake_osutils.popens[0][0][0][2]
         import_statement = pip_execution_string.split(';')[1].strip()
         assert import_statement == expected_import_statement
+
+    def test_check_pip_runner_string_pip(self):
+        fake_osutils = FakePopenOSUtils([FakePopen(0, '', '')])
+        pip = SubprocessPip(osutils=fake_osutils,
+                            python_exe=sys.executable)
+        pip.main(['--version'])
+
+        pip_runner_string = fake_osutils.popens[0][0][0][2].split(";")[-1:][0]
+        self.assertIn("main", pip_runner_string)