lit: modernize the lit configuration for the lit tests

[stella.stamenova]

Summary

This also normalizes the config feature that represents the windows platform to "system-windows" as opposed to having both "windows" and "system-windows"

[mgorny]

This breaks running tests via lit:

$ lit -v tests
lit: /usr/lib/python3.7/site-packages/lit/TestingConfig.py:102: fatal: unable to parse config file '/home/mgorny/git/llvm-project/llvm/utils/lit/tests/lit.cfg', traceback: Traceback (most recent call last):
  File "/usr/lib/python3.7/site-packages/lit/TestingConfig.py", line 89, in load_from_path
    exec(compile(data, path, 'exec'), cfg_globals, None)
  File "/home/mgorny/git/llvm-project/llvm/utils/lit/tests/lit.cfg", line 38, in <module>
    llvm_config.with_environment('PYTHONPATH', lit_path, append_path=True)
AttributeError: 'NoneType' object has no attribute 'with_environment'

utils/lit/tests/lit.cfg

 # -*- Python -*-
 
 import os
 import sys
 
 import lit.formats
+from lit.llvm import llvm_config
 
 # Configuration file for the 'lit' test runner.
 
 # name: The name of this test suite.
 config.name = 'lit'
 
 # testFormat: The test format to use to interpret tests.
 config.test_format = lit.formats.ShTest(execute_external=False)
 
 # suffixes: A list of file extensions to treat as test files.
 config.suffixes = ['.py']
 
 # excludes: A list of individual files to exclude.
 config.excludes = ['Inputs']
 
 # test_source_root: The root path where tests are located.
 config.test_source_root = os.path.dirname(__file__)
 config.test_exec_root = config.test_source_root
 
 config.target_triple = '(unused)'
 
-src_root = os.path.join(config.test_source_root, '..')
 llvm_src_root = getattr(config, 'llvm_src_root', None)
-if llvm_src_root != None:
-  # ``src_root`` may be in LLVM's binary build directory which does not contain
+if llvm_src_root:
+  # ``test_source_root`` may be in LLVM's binary build directory which does not contain
   # ``lit.py``, so use `llvm_src_root` instead.
   lit_path = os.path.join(llvm_src_root, 'utils', 'lit')
 else:
-  lit_path = src_root
+  lit_path = os.path.join(config.test_source_root, '..')
 
-pythonpath_list = [lit_path] # Required because some tests import the lit module
+# Required because some tests import the lit module
+llvm_config.with_environment('PYTHONPATH', lit_path, append_path=True)
 
-# Ensure the user's PYTHONPATH is included.
-if 'PYTHONPATH' in os.environ:
-    pythonpath_list.append(os.environ['PYTHONPATH'])
-if 'PYTHONPATH' in config.environment:
-    pythonpath_list.append(config.environment['PYTHONPATH'])
-config.environment['PYTHONPATH'] = os.pathsep.join(pythonpath_list)
+# Add llvm and lit tools directories if this config is being loaded indirectly.
+for attribute in ('llvm_tools_dir', 'lit_tools_dir'):
+    directory = getattr(config, attribute, None)
+    if directory:
+        llvm_config.with_environment('PATH', directory, append_path=True)
 
-config.substitutions.append(('%{src_root}', src_root))
 config.substitutions.append(('%{inputs}', os.path.join(
-            src_root, 'tests', 'Inputs')))
+    config.test_source_root, 'Inputs')))
 config.substitutions.append(('%{lit}', "%%{python} %s" % (
-            os.path.join(lit_path, 'lit.py'),)))
 config.substitutions.append(('%{python}', '"%s"' % (sys.executable)))
 
-
 # Enable coverage.py reporting, assuming the coverage module has been installed
 # and sitecustomize.py in the virtualenv has been modified appropriately.
 if lit_config.params.get('check-coverage', None):
     config.environment['COVERAGE_PROCESS_START'] = os.path.join(
         os.path.dirname(__file__), ".coveragerc")
 
-# Add a feature to detect the Python version.
-config.available_features.add("python%d.%d" % (sys.version_info[0],
-                                                  sys.version_info[1]))
-
 # Add a feature to detect if psutil is available
 try:
     import psutil
     lit_config.note('Found python psutil module')
     config.available_features.add("python-psutil")
 except ImportError:
     lit_config.warning('Could not import psutil. Some tests will be skipped and'
                        ' the --timeout command line argument will not work.')
-
-if sys.platform.startswith('win') or sys.platform.startswith('cygwin'):
-    config.available_features.add('windows')
-
-# Add llvm and lit tools directories if this config is being loaded indirectly.
-path = config.environment['PATH']
-for attribute in ('llvm_tools_dir', 'lit_tools_dir'):
-    directory = getattr(config, attribute, None)
-    if directory:
-        path = os.path.pathsep.join((directory, path))
-config.environment['PATH'] = path

utils/lit/tests/lit.site.cfg.in

 # This is used when we can't determine the tool dir at configuration time.
 try:
     config.llvm_tools_dir = config.llvm_tools_dir % lit_config.params
 except KeyError:
     e = sys.exc_info()[1]
     key, = e.args
     lit_config.fatal("unable to find %r parameter, use '--param=%s=VALUE'" % (key,key))
 
+import lit.llvm
+lit.llvm.initialize(lit_config, config)
+
 # Let the main config do the real work.
 lit_config.load_config(config, "@LLVM_BINARY_DIR@/utils/lit/tests/lit.cfg")

utils/lit/tests/shtest-timeout.py

 # REQUIRES: python-psutil
 
 # llvm.org/PR33944
-# This should be system-windows as windows does not cover all cases, but
-# apparently neither does system-windows
-# UNSUPPORTED: windows
+# UNSUPPORTED: system-windows
 
 # FIXME: This test is fragile because it relies on time which can
 # be affected by system performance. In particular we are currently
 # assuming that `short.py` can be successfully executed within 2
 # seconds of wallclock time.
 
 # Test per test timeout using external shell
 # RUN: not %{lit} \