[Build System: Python] Cleaned-up the python_lint.py script.

utils/python_lint.py

@@ -1,29 +1,45 @@
 #!/usr/bin/env python
-# python_lint.py - Runs flake8 linting over the repository ------*- python -*-
-#
+
 # This source file is part of the Swift.org open source project
 #
-# Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+# Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
 # Licensed under Apache License v2.0 with Runtime Library Exception
 #
 # See https://swift.org/LICENSE.txt for license information
 # See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 #
 
-from __future__ import print_function
+
+"""
+Utility script used to run the flake8 linter over all the project Python
+sources.
+"""
+
+
+from __future__ import absolute_import, print_function, unicode_literals
 
 import os
 import subprocess
 import sys
 
 
-def lint(arguments, verbose=True):
-    flake8_result = subprocess.call(
-        [sys.executable, "-c", "import flake8; import flake8_import_order"]
-    )
-    if flake8_result != 0:
-        if verbose:
-            print("""
+__all__ = [
+    'lint',
+]
+
+
+# -----------------------------------------------------------------------------
+# Constants
+
+_UTILS_DIR = os.path.abspath(os.path.dirname(__file__))
+_PROJECT_DIR = os.path.dirname(_UTILS_DIR)
+
+_REQUIRED_PACKAGES = [
+    'flake8',
+    'flake8-import-order',
+]
+
+_INSTALL_FLAKE8_MESSAGE = """
 The flake8 and flake8-import-order Python packages are required for linting,
 but these were not found on your system.
 
@@ -32,25 +48,49 @@ You can install these using:
     python -m pip install flake8
     python -m pip install flake8-import-order
 
-For more help, see http://flake8.pycqa.org.""")
+For more help, see http://flake8.pycqa.org.
+"""
 
-        # We should be returning `flake8_result` from here.  However,
-        # some Python files lint themselves using embedded doctests,
-        # which causes CI smoke tests to fail because the Linux nodes
-        # do not have these modules installed.
+
+# -----------------------------------------------------------------------------
+# Helpers
+
+def _is_package_installed(name):
+    """Runs the pip command to check if a package is installed.
+    """
+
+    command = [
+        sys.executable,
+        '-m', 'pip',
+        'show', '--quiet',
+        name,
+    ]
+
+    with open(os.devnull, 'w') as devnull:
+        status = subprocess.call(command, stderr=devnull)
+
+    return not status
+
+
+# -----------------------------------------------------------------------------
+
+def lint(args, verbose=False):
+    all_packages_installed = all([
+        _is_package_installed(name)
+        for name in _REQUIRED_PACKAGES
+    ])
+
+    if not all_packages_installed:
+        if verbose:
+            print(_INSTALL_FLAKE8_MESSAGE)
 
         return 0
 
-    utils_directory = os.path.dirname(os.path.abspath(__file__))
-    parent_directory = os.path.dirname(utils_directory)
-    linting_result = subprocess.call(
-        [sys.executable, "-m", "flake8"] + arguments,
-        cwd=parent_directory,
-        universal_newlines=True
-    )
-    return linting_result
+    return subprocess.call(
+        [sys.executable, '-m', 'flake8'] + args,
+        cwd=_PROJECT_DIR,
+        universal_newlines=True)
 
 
 if __name__ == '__main__':
-    linting_result = lint(sys.argv[1:])
-    sys.exit(linting_result)
+    sys.exit(lint(sys.argv[1:], verbose=True))