[lit] Remove (or allow specific) unused imports

Summary:
Using Python linter flake8 on the utils/lit reveals several linter
warnings designated "F401: Unused import". Fix or silence these
warnings.

Some of these unused imports are legitimate, while some are part of lit's API.
For example, users of lit expect to be able to access `lit.formats.ShTest` in
their `lit.cfg`, despite the module hierarchy for that symbol actually being
`lit.formats.shtest.ShTest`. To silence linter errors for these lines,
include a "noqa" directive.

Reviewers: echristo, delcypher, beanz, ddunbar

Subscribers: mehdi_amini, llvm-commits

Differential Revision: https://reviews.llvm.org/D25407

llvm-svn: 283710

utils/lit/lit.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python
 
+from lit.main import main
+
 if __name__=='__main__':
-    import lit
-    lit.main()
+    main()

utils/lit/lit/LitConfig.py

@@ -83,7 +83,7 @@ class LitConfig(object):
             # a timeout per test. Check it's available.
             # See lit.util.killProcessAndChildren()
             try:
-                import psutil
+                import psutil  # noqa: F401
             except ImportError:
                 self.fatal("Setting a timeout per test requires the"
                            " Python psutil module but it could not be"

utils/lit/lit/__init__.py

@@ -1,8 +1,5 @@
 """'lit' Testing Tool"""
 
-from __future__ import absolute_import
-from .main import main
-
 __author__ = 'Daniel Dunbar'
 __email__ = 'daniel@minormatter.com'
 __versioninfo__ = (0, 6, 0)

utils/lit/lit/formats/__init__.py

@@ -1,4 +1,8 @@
-from __future__ import absolute_import
-from lit.formats.base import TestFormat, FileBasedTest, OneCommandPerFileTest
-from lit.formats.googletest import GoogleTest
-from lit.formats.shtest import ShTest
+from lit.formats.base import (  # noqa: F401
+    TestFormat,
+    FileBasedTest,
+    OneCommandPerFileTest
+)
+
+from lit.formats.googletest import GoogleTest  # noqa: F401
+from lit.formats.shtest import ShTest  # noqa: F401