[scan-build-py] Increase precision of timestamp in report directory name

[dcoughlin]

Summary

This patch improves compatibility with the perl version of scan-build.

The perl version of scan-build produces output report directories with increasing lexicographic ordering. This ordering is relied on by the CmpRuns.py tool in utils/analyzer when comparing results for build commands with multiple steps. That tool tries to line up the output directory for each step between different runs of the analyzer based on the increasing directory name.

The python version of scan-build uses tmp file.mkdtemp() with a time stamp prefix to create report directories. The timestamp has a 1-second precision. This means that when analysis of a single build step takes less than a second the ordering property that CmpRuns.py expects will sometimes not hold, depending on the timing and the random suffix generated by mkdtemp(). Ultimately this causes CmpRuns to incorrectly correlate results from build steps and report spurious differences between runs.

To fix this, I propose increasing the precision of the timestamp used in scan-build-py to the microsecond level. This approach still has the same underlying issue -- but in practice, analysis of any build step is unlikely to take less than a millisecond.

What do you think?

[rizsotto.mailinglist]

looks good to me. i like the test. :) but would keep the pep8 cleanness.

tools/scan-build-py/libscanbuild/report.py

38–39

this line length's is 80, which breaks the pep8 check. (would kill some of the -)

[dcoughlin]

Fix the pep8 79-column violation.

tools/scan-build-py/libscanbuild/report.py

 import time
 import tempfile
 import itertools
 import plistlib
 import glob
 import json
 import logging
 import contextlib
+import datetime
 from libscanbuild import duplicate_check
 from libscanbuild.clang import get_version
 
 __all__ = ['report_directory', 'document']
 
 
 @contextlib.contextmanager
 def report_directory(hint, keep):
     """ Responsible for the report directory.
 
     hint -- could specify the parent directory of the output directory.
     keep -- a boolean value to keep or delete the empty report directory. """
 
-    stamp = time.strftime('scan-build-%Y-%m-%d-%H%M%S-', time.localtime())
+    stamp_format = 'scan-build-%Y-%m-%d-%H-%M-%S-%f-'
+    stamp = datetime.datetime.now().strftime(stamp_format)
 
     parentdir = os.path.abspath(hint)
     if not os.path.exists(parentdir):
         os.makedirs(parentdir)
 
     name = tempfile.mkdtemp(prefix=stamp, dir=parentdir)
 
     logging.info('Report directory created: %s', name)

tools/scan-build-py/tests/unit/test_report.py

class GetPrefixFromCompilationDatabaseTest(unittest.TestCase):
 
     def test_with_single_file(self):
         self.assertEqual(
             sut.commonprefix(['/tmp/a.c']), '/tmp')
 
     def test_empty(self):
         self.assertEqual(
             sut.commonprefix([]), '')
+
+class ReportDirectoryTest(unittest.TestCase):
+
+    # Test that successive report directory names ascend in lexicographic
+    # order. This is required so that report directories from two runs of
+    # scan-build can be easily matched up to compare results.
+    def test_directory_name_comparison(self):
+        with libear.TemporaryDirectory() as tmpdir, \
+             sut.report_directory(tmpdir, False) as report_dir1, \
+             sut.report_directory(tmpdir, False) as report_dir2, \
+             sut.report_directory(tmpdir, False) as report_dir3:
+            self.assertLess(report_dir1, report_dir2)
+            self.assertLess(report_dir2, report_dir3)