Close files opened by Scanner, Loader

We're seeing noise like the following in doc builds:

  /foo/.tox/docs/lib/python3.9/site-packages/docutils/statemachine.py:707:
  ResourceWarning: unclosed file <_io.BufferedReader name='/foo/.git/objects/pack/pack-dd69481843ca1b7377f2f109b0022221437aca20.pack'>
    if not hasattr(pattern, 'match'):
  ResourceWarning: Enable tracemalloc to get the object allocation traceback

Enable tracemalloc for Sphinx gives us the 'Loader' as the root cause:

  $ python -W all::ResourceWarning -X tracemalloc=100 -m sphinx.cmd.build ...
  ...
  File "/foo/.tox/docs/lib/python3.9/site-packages/reno/sphinxext.py", lineno 114
    ldr = loader.Loader(conf)
  File "/foo/.tox/docs/lib/python3.9/site-packages/reno/loader.py", lineno 63
    self._load_data()
  ...

(you could also use PYTHONTRACEMALLOC and PYTHONWARNINGS env vars)

Following this thread, it appears 'reno.scanner.Scanner' creates an
instance of 'dulwich.repo.Repo', however, it fails to close it [1]. The
'reno.loader.Loader' uses 'Scanner', meaning this also leaves around
open files.

The solution is simple: add a 'close()' method to both the 'Scanner' and
'Loader', and provide the necessary '__enter__' and '__exit__' magic
methods to use it as a context manager, like the 'Repo' object itself
supports.

[1] https://www.dulwich.io/docs/api/dulwich.repo.html#dulwich.repo.Repo.close

Change-Id: I0b9776f431cf902a9ace5d52961eb77caaae8eaa
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

releasenotes/notes/scanner-loader-context-managers-5d80d95dc3d33fe0.yaml

@@ -0,0 +1,31 @@
+---
+fixes:
+  - |
+    Instances of ``reno.scanner.Scanner`` and ``reno.loader.Loader`` will now
+    corectly close all open files related to the scanned Git repo when the
+    ``close()`` method is called. Alternatively, these classes may be used as
+    a context manager. Previously, Python would attempt to close these files
+    itself, resulting in a ``ResourceWarning`` warning being emitted.
+features:
+  - |
+    The ``reno.scanner.Scanner`` and ``reno.loader.Loader`` classes can now
+    be used as context managers. For example::
+
+        import reno.scannner
+
+        with reno.scanner.Scanner(...) as scanner:
+            pass
+
+    This will ensure any open files pertaining to the scanned Git repo are
+    correctly closed, avoiding ``ResourceWarning`` instances otherwise seen.
+
+    A ``close()`` method is also provided for both, allowing use outside of
+    context managers. For example::
+
+        import reno.loader
+
+        loader = reno.loader.Loader(...)
+        try:
+            pass
+        finally:
+            loader.close()

reno/cache.py

@@ -21,50 +21,48 @@ from reno import scanner
 
 
 def build_cache_db(conf, versions_to_include):
-    s = scanner.Scanner(conf)
+    with scanner.Scanner(conf) as s:
+        branches = [conf.branch]
+        if not conf.branch:  # if no branch requested, scan all
+            branches += s.get_series_branches()
 
-    branches = [conf.branch]
-    if not conf.branch:  # if no branch requested, scan all
-        branches += s.get_series_branches()
+        notes = collections.OrderedDict()
+        for branch in branches:
+            notes.update(s.get_notes_by_version(branch))
 
-    notes = collections.OrderedDict()
-    for branch in branches:
-        notes.update(s.get_notes_by_version(branch))
+        # Default to including all versions returned by the scanner.
+        if not versions_to_include:
+            versions_to_include = list(notes.keys())
 
-    # Default to including all versions returned by the scanner.
-    if not versions_to_include:
-        versions_to_include = list(notes.keys())
+        # Build a cache data structure including the file contents as well
+        # as the basic data returned by the scanner.
+        file_contents = {}
+        for version in versions_to_include:
+            for filename, sha in notes[version]:
+                body = s.get_file_at_commit(filename, sha)
+                # We want to save the contents of the file, which is YAML,
+                # inside another YAML file. That looks terribly ugly with
+                # all of the escapes needed to format it properly as
+                # embedded YAML, so parse the input and convert it to a
+                # data structure that can be serialized cleanly.
+                y = yaml.safe_load(body)
+                file_contents[filename] = y
 
-    # Build a cache data structure including the file contents as well
-    # as the basic data returned by the scanner.
-    file_contents = {}
-    for version in versions_to_include:
-        for filename, sha in notes[version]:
-            body = s.get_file_at_commit(filename, sha)
-            # We want to save the contents of the file, which is YAML,
-            # inside another YAML file. That looks terribly ugly with
-            # all of the escapes needed to format it properly as
-            # embedded YAML, so parse the input and convert it to a
-            # data structure that can be serialized cleanly.
-            y = yaml.safe_load(body)
-            file_contents[filename] = y
-
-    cache = {
-        'notes': [
-            {'version': k, 'files': v}
-            for k, v in notes.items()
-        ],
-        'dates': [
-            {'version': k, 'date': v}
-            for k, v in s.get_version_dates().items()
-        ],
-        'file-contents': file_contents,
-    }
-    return cache
+        cache = {
+            'notes': [
+                {'version': k, 'files': v}
+                for k, v in notes.items()
+            ],
+            'dates': [
+                {'version': k, 'date': v}
+                for k, v in s.get_version_dates().items()
+            ],
+            'file-contents': file_contents,
+        }
+        return cache
 
 
-def write_cache_db(conf, versions_to_include,
-                   outfilename=None):
+def write_cache_db(conf, versions_to_include, outfilename=None):
     """Create a cache database file for the release notes data.
 
     Build the cache database from scanning the project history and

reno/linter.py

@@ -27,22 +27,24 @@ def lint_cmd(args, conf):
     notes = glob.glob(os.path.join(notesdir, '*.yaml'))
 
     error = 0
-    load = loader.Loader(conf, ignore_cache=True)
     allowed_section_names = [conf.prelude_section_name] + \
                             [s[0] for s in conf.sections]
 
     uids = {}
-    for f in notes:
-        LOG.debug('examining %s', f)
-        uid = scanner._get_unique_id(f)
-        uids.setdefault(uid, []).append(f)
+    with loader.Loader(conf, ignore_cache=True) as ldr:
+        for f in notes:
+            LOG.debug('examining %s', f)
+            uid = scanner._get_unique_id(f)
+            uids.setdefault(uid, []).append(f)
 
-        content = load.parse_note_file(f, None)
-        for section_name in content.keys():
-            if section_name not in allowed_section_names:
-                LOG.warning('unrecognized section name %s in %s',
-                            section_name, f)
-                error = 1
+            content = ldr.parse_note_file(f, None)
+            for section_name in content.keys():
+                if section_name not in allowed_section_names:
+                    LOG.warning(
+                        'unrecognized section name %s in %s',
+                        section_name, f,
+                    )
+                    error = 1
 
     for uid, names in sorted(uids.items()):
         if len(names) > 1:

reno/lister.py

@@ -21,16 +21,16 @@ def list_cmd(args, conf):
     "List notes files based on query arguments"
     LOG.debug('starting list')
     reporoot = conf.reporoot
-    ldr = loader.Loader(conf)
-    if args.version:
-        versions = args.version
-    else:
-        versions = ldr.versions
-    for version in versions:
-        notefiles = ldr[version]
-        print(version)
-        for n, sha in notefiles:
-            if n.startswith(reporoot):
-                n = n[len(reporoot):]
-            print('\t%s (%s)' % (n, sha))
+    with loader.Loader(conf) as ldr:
+        if args.version:
+            versions = args.version
+        else:
+            versions = ldr.versions
+        for version in versions:
+            notefiles = ldr[version]
+            print(version)
+            for n, sha in notefiles:
+                if n.startswith(reporoot):
+                    n = n[len(reporoot):]
+                print('\t%s (%s)' % (n, sha))
     return

reno/loader.py

@@ -30,8 +30,7 @@ def get_cache_filename(conf):
 class Loader(object):
     "Load the release notes for a given repository."
 
-    def __init__(self, conf,
-                 ignore_cache=False):
+    def __init__(self, conf, ignore_cache=False):
         """Initialize a Loader.
 
         The versions are presented in reverse chronological order.
@@ -70,24 +69,37 @@ class Loader(object):
 
         if (not self._ignore_cache) and cache_file_exists:
             LOG.debug('loading cache file %s', self._cache_filename)
+
             with open(self._cache_filename, 'r', encoding=self._encoding) as f:
                 self._cache = yaml.safe_load(f.read())
-                # Save the cached scanner output to the same attribute
-                # it would be in if we had loaded it "live". This
-                # simplifies some of the logic in the other methods.
-                self._scanner_output = collections.OrderedDict(
-                    (n['version'], n['files'])
-                    for n in self._cache['notes']
-                )
-                self._tags_to_dates = collections.OrderedDict(
-                    (n['version'], n['date'])
-                    for n in self._cache['dates']
-                )
+
+            # Save the cached scanner output to the same attribute
+            # it would be in if we had loaded it "live". This
+            # simplifies some of the logic in the other methods.
+            self._scanner_output = collections.OrderedDict(
+                (n['version'], n['files'])
+                for n in self._cache['notes']
+            )
+            self._tags_to_dates = collections.OrderedDict(
+                (n['version'], n['date'])
+                for n in self._cache['dates']
+            )
         else:
             self._scanner = scanner.Scanner(self._config)
             self._scanner_output = self._scanner.get_notes_by_version()
             self._tags_to_dates = self._scanner.get_version_dates()
 
+    def close(self):
+        """Close any files opened by this loader."""
+        if self._scanner is not None:
+            self._scanner.close()
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        self.close()
+
     @property
     def versions(self):
         "A list of all of the versions found."

reno/report.py

@@ -16,20 +16,22 @@ from reno import loader
 
 def report_cmd(args, conf):
     "Generates a release notes report"
-    ldr = loader.Loader(conf)
     encoding = conf.options['encoding']
-    if args.version:
-        versions = args.version
-    else:
-        versions = ldr.versions
-    text = formatter.format_report(
-        ldr,
-        conf,
-        versions,
-        title=args.title,
-        show_source=args.show_source,
-        branch=args.branch,
-    )
+
+    with loader.Loader(conf) as ldr:
+        if args.version:
+            versions = args.version
+        else:
+            versions = ldr.versions
+        text = formatter.format_report(
+            ldr,
+            conf,
+            versions,
+            title=args.title,
+            show_source=args.show_source,
+            branch=args.branch,
+        )
+
     if args.output:
         with open(args.output, 'w', encoding=encoding) as f:
             f.write(text)

reno/scanner.py

@@ -533,6 +533,16 @@ class Scanner(object):
         )
         self._encoding = conf.options['encoding']
 
+    def close(self):
+        """Close any files opened by this scanner."""
+        self._repo.close()
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        self.close()
+
     def _get_ref(self, name):
         if name:
             candidates = [

reno/semver.py

@@ -22,76 +22,85 @@ LOG = logging.getLogger(__name__)
 def compute_next_version(conf):
     "Compute the next semantic version based on the available release notes."
     LOG.debug('starting semver-next')
-    ldr = loader.Loader(conf, ignore_cache=True)
-    LOG.debug('known versions: %s', ldr.versions)
+    with loader.Loader(conf, ignore_cache=True) as ldr:
+        LOG.debug('known versions: %s', ldr.versions)
 
-    # We want to include any notes in the local working directory or
-    # in any commits that came after the last tag. We should never end
-    # up with more than 2 entries in to_include.
-    to_include = []
-    for to_consider in ldr.versions:
-        if to_consider == '*working-copy*':
-            to_include.append(to_consider)
-            continue
-        # This check relies on PEP 440 versioning
-        parsed = version.Version(to_consider)
-        if parsed.post:
-            to_include.append(to_consider)
-            continue
-        break
+        # We want to include any notes in the local working directory or
+        # in any commits that came after the last tag. We should never end
+        # up with more than 2 entries in to_include.
+        to_include = []
+        for to_consider in ldr.versions:
+            if to_consider == '*working-copy*':
+                to_include.append(to_consider)
+                continue
 
-    # If we found no commits then we're sitting on a real tag and
-    # there is nothing to do to update the version.
-    if not to_include:
-        LOG.debug('found no staged notes and no post-release commits')
-        return ldr.versions[0]
+            # This check relies on PEP 440 versioning
+            parsed = version.Version(to_consider)
+            if parsed.post:
+                to_include.append(to_consider)
+                continue
 
-    LOG.debug('including notes from %s', to_include)
+            break
 
-    candidate_bases = to_include[:]
-    if candidate_bases[0] == '*working-copy*':
-        candidate_bases = candidate_bases[1:]
+        # If we found no commits then we're sitting on a real tag and
+        # there is nothing to do to update the version.
+        if not to_include:
+            LOG.debug('found no staged notes and no post-release commits')
+            return ldr.versions[0]
 
-    if not candidate_bases:
-        # We have a real tag and some locally modified files. Use the
-        # real tag as the basis of the next version.
-        base_version = version.Version(ldr.versions[1])
-    else:
-        base_version = version.Version(candidate_bases[0])
+        LOG.debug('including notes from %s', to_include)
 
-    LOG.debug('base version %s', base_version)
+        candidate_bases = to_include[:]
+        if candidate_bases[0] == '*working-copy*':
+            candidate_bases = candidate_bases[1:]
 
-    inc_minor = False
-    inc_patch = False
-    for ver in to_include:
-        for filename, sha in ldr[ver]:
-            notes = ldr.parse_note_file(filename, sha)
-            for section in conf.semver_major:
-                if notes.get(section, []):
-                    LOG.debug('found breaking change in %r section of %s',
-                              section, filename)
-                    return '{}.0.0'.format(base_version.major + 1)
-            for section in conf.semver_minor:
-                if notes.get(section, []):
-                    LOG.debug('found feature in %r section of %s',
-                              section, filename)
-                    inc_minor = True
-                    break
-            for section in conf.semver_patch:
-                if notes.get(section, []):
-                    LOG.debug('found bugfix in %r section of %s',
-                              section, filename)
-                    inc_patch = True
-                    break
+        if not candidate_bases:
+            # We have a real tag and some locally modified files. Use the
+            # real tag as the basis of the next version.
+            base_version = version.Version(ldr.versions[1])
+        else:
+            base_version = version.Version(candidate_bases[0])
+
+        LOG.debug('base version %s', base_version)
+
+        inc_minor = False
+        inc_patch = False
+
+        for ver in to_include:
+            for filename, sha in ldr[ver]:
+                notes = ldr.parse_note_file(filename, sha)
+
+                for section in conf.semver_major:
+                    if notes.get(section, []):
+                        LOG.debug('found breaking change in %r section of %s',
+                                  section, filename)
+                        return '{}.0.0'.format(base_version.major + 1)
+
+                for section in conf.semver_minor:
+                    if notes.get(section, []):
+                        LOG.debug('found feature in %r section of %s',
+                                  section, filename)
+                        inc_minor = True
+                        break
+
+                for section in conf.semver_patch:
+                    if notes.get(section, []):
+                        LOG.debug('found bugfix in %r section of %s',
+                                  section, filename)
+                        inc_patch = True
+                        break
 
     major = base_version.major
     minor = base_version.minor
     patch = base_version.micro
+
     if inc_patch:
         patch += 1
+
     if inc_minor:
         minor += 1
         patch = 0
+
     return '{}.{}.{}'.format(major, minor, patch)
 
 

reno/setup_command.py

@@ -127,13 +127,15 @@ class BuildReno(cmd.Command):
         )
         log.info('wrote cache file to %s', cache_filename)
 
-        ldr = loader.Loader(conf)
-        text = formatter.format_report(
-            ldr,
-            conf,
-            ldr.versions,
-            title=self.distribution.metadata.name,
-        )
+        with loader.Loader(conf) as ldr:
+            text = formatter.format_report(
+                ldr,
+                conf,
+                ldr.versions,
+                title=self.distribution.metadata.name,
+            )
+
         with open(self.output_file, 'w') as f:
             f.write(text)
+
         log.info('wrote release notes to %s', self.output_file)

reno/sphinxext.py

@@ -111,22 +111,23 @@ class ReleaseNotesDirective(rst.Directive):
                  os.path.join(conf.reporoot, notesdir),
                  branch or 'current branch'))
 
-        ldr = loader.Loader(conf)
-        if version_opt is not None:
-            versions = [
-                v.strip()
-                for v in version_opt.split(',')
-            ]
-        else:
-            versions = ldr.versions
-        LOG.info('got versions %s' % (versions,))
-        text = formatter.format_report(
-            ldr,
-            conf,
-            versions,
-            title=title,
-            branch=branch,
-        )
+        with loader.Loader(conf) as ldr:
+            if version_opt is not None:
+                versions = [
+                    v.strip()
+                    for v in version_opt.split(',')
+                ]
+            else:
+                versions = ldr.versions
+            LOG.info('got versions %s' % (versions,))
+            text = formatter.format_report(
+                ldr,
+                conf,
+                versions,
+                title=title,
+                branch=branch,
+            )
+
         source_name = '<%s %s>' % (__name__, branch or 'current branch')
         result = statemachine.ViewList()
         for line_num, line in enumerate(text.splitlines(), 1):

reno/tests/test_formatter.py

@@ -49,6 +49,13 @@ class TestFormatterBase(base.TestCase):
                 ignore_cache=False,
             )
 
+    def tearDown(self):
+        # we don't need to worry about closing this after since we're not
+        # actually using a real Git repo here (see the mock above), but we'll
+        # do so to enforce the contract
+        self.ldr.close()
+        super().tearDown()
+
 
 class TestFormatter(TestFormatterBase):
 

reno/tests/test_loader.py

@@ -65,8 +65,8 @@ class TestValidate(base.TestCase):
           This is a single string. It should be converted to a list.
         """))
         self.assertIsInstance(note_bodies['issues'], str)
-        ldr = self._make_loader(note_bodies)
-        parse_results = ldr.parse_note_file('note1', None)
+        with self._make_loader(note_bodies) as ldr:
+            parse_results = ldr.parse_note_file('note1', None)
         self.assertIsInstance(parse_results['issues'], list)
 
     def test_invalid_note_with_prelude_as_list(self):
@@ -75,8 +75,8 @@ class TestValidate(base.TestCase):
           - The prelude should not be a list.
         '''))
         self.assertIsInstance(note_bodies['prelude'], list)
-        ldr = self._make_loader(note_bodies)
-        ldr.parse_note_file('note1', None)
+        with self._make_loader(note_bodies) as ldr:
+            ldr.parse_note_file('note1', None)
         self.assertIn('does not parse as a single string', self.logger.output)
 
     def test_invalid_note_with_colon_as_dict(self):
@@ -86,8 +86,8 @@ class TestValidate(base.TestCase):
           - dict: But this is parsed as a mapping (dictionary), which is bad.
         '''))
         self.assertIsInstance(note_bodies['issues'][-1], dict)
-        ldr = self._make_loader(note_bodies)
-        ldr.parse_note_file('note1', None)
+        with self._make_loader(note_bodies) as ldr:
+            ldr.parse_note_file('note1', None)
         self.assertIn('instead of a string', self.logger.output)
 
     def test_invalid_note_with_unrecognized_key(self):
@@ -98,8 +98,8 @@ class TestValidate(base.TestCase):
           This is an issue but we're using an unrecognized section key.
         '''))
         self.assertIsInstance(note_bodies, dict)
-        ldr = self._make_loader(note_bodies)
-        ldr.parse_note_file('note1', None)
+        with self._make_loader(note_bodies) as ldr:
+            ldr.parse_note_file('note1', None)
         self.assertIn(
             'The foobar section of note1 is not a recognized section.',
             self.logger.output)
@@ -114,8 +114,8 @@ class TestValidate(base.TestCase):
           This is an issue but we're missing the top-level 'issues' key.
         '''))
         self.assertIsInstance(note_bodies, list)
-        ldr = self._make_loader(note_bodies)
-        self.assertRaises(ValueError, ldr.parse_note_file, 'note1', None)
+        with self._make_loader(note_bodies) as ldr:
+            self.assertRaises(ValueError, ldr.parse_note_file, 'note1', None)
         self.assertIn(
             'does not appear to be structured as a YAML mapping',
             self.logger.output)

reno/tests/test_scanner.py

@@ -217,8 +217,8 @@ class BasicTest(Base):
 
     def test_non_python_no_tags(self):
         filename = self._add_notes_file()
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -231,8 +231,8 @@ class BasicTest(Base):
     def test_python_no_tags(self):
         self._make_python_package()
         filename = self._add_notes_file()
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -246,8 +246,8 @@ class BasicTest(Base):
         filename = self._add_notes_file()
         self.repo.add_file('not-a-release-note.txt')
         self.repo.git('tag', '-s', '-m', 'first tag', '1.0.0')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -260,8 +260,8 @@ class BasicTest(Base):
     def test_note_commit_tagged(self):
         filename = self._add_notes_file()
         self.repo.git('tag', '-s', '-m', 'first tag', '1.0.0')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -274,8 +274,8 @@ class BasicTest(Base):
     def test_tag_with_v_prefix(self):
         filename = self._add_notes_file()
         self.repo.git('tag', '-s', '-m', 'tag with v prefix', 'v1.0.0')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -289,8 +289,8 @@ class BasicTest(Base):
         self._make_python_package()
         self.repo.git('tag', '-s', '-m', 'first tag', '1.0.0')
         filename = self._add_notes_file()
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -305,8 +305,8 @@ class BasicTest(Base):
         self.repo.git('tag', '-s', '-m', 'first tag', '1.0.0rc1')
         self.repo.git('tag', '-s', '-m', 'first tag', '1.0.0')
         filename = self._add_notes_file()
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -321,8 +321,8 @@ class BasicTest(Base):
         self.repo.add_file('ignore-1.txt')
         self.repo.git('tag', '-s', '-m', 'first tag', '1.0.0')
         self.repo.add_file('ignore-2.txt')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -337,8 +337,8 @@ class BasicTest(Base):
         self.repo.git('tag', '-s', '-m', 'first tag', '1.0.0')
         f1 = self._add_notes_file()
         f2 = self._add_notes_file()
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -353,8 +353,8 @@ class BasicTest(Base):
         f1 = self._add_notes_file(commit=False)
         f2 = self._add_notes_file()
         self.repo.git('tag', '-s', '-m', 'first tag', '1.0.0')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -370,8 +370,8 @@ class BasicTest(Base):
         f1 = self._add_notes_file()
         self.repo.git('tag', '-s', '-m', 'first tag', '2.0.0')
         f2 = self._add_notes_file()
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -391,8 +391,8 @@ class BasicTest(Base):
         f2 = f1.replace('slug1', 'slug2')
         self.repo.git('mv', f1, f2)
         self.repo.commit('rename note file')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -411,8 +411,8 @@ class BasicTest(Base):
         f2 = f1.replace('slug1', 'slug0')
         self.repo.git('mv', f1, f2)
         self.repo.commit('rename note file')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -431,8 +431,8 @@ class BasicTest(Base):
         with open(os.path.join(self.reporoot, f1), 'w') as f:
             f.write('---\npreamble: new contents for file')
         self.repo.commit('edit note file')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -451,8 +451,8 @@ class BasicTest(Base):
         f2 = f1.replace('slug1', 'slug2')
         self.repo.git('mv', f1, f2)
         self.repo.commit('rename note file')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -474,8 +474,8 @@ class BasicTest(Base):
                         'slug1-0000000000000001')
         self.repo.git('mv', f1, f2)
         self.repo.commit('rename note file')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -497,8 +497,8 @@ class BasicTest(Base):
         self.c.override(
             earliest_version='2.0.0',
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -518,8 +518,8 @@ class BasicTest(Base):
         self.repo.git('rm', f1)
         self.repo.commit('remove note file')
         self.repo.git('tag', '-s', '-m', 'first tag', '2.0.0')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -546,8 +546,8 @@ class BasicTest(Base):
                                     '--pretty=%H %d',
                                     '--name-only')
         self.addDetail('git log', text_content(log_results))
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -573,8 +573,8 @@ class BasicTest(Base):
         status_results = self.repo.git('status')
         self.addDetail('git status', text_content(status_results))
         # Now run the scanner
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         self.assertEqual(
             {'*working-copy*': [
                 (os.path.join('releasenotes', 'notes', basename),
@@ -598,8 +598,8 @@ class BasicTest(Base):
         status_results = self.repo.git('status')
         self.addDetail('git status', text_content(status_results))
         # Now run the scanner
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         # Take the staged version of the file, but associate it with
         # tagged version 1.0.0 because the file was added before that
         # version.
@@ -623,8 +623,8 @@ class BasicTest(Base):
         status_results = self.repo.git('status')
         self.addDetail('git status', text_content(status_results))
         # Now run the scanner
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         # Take the staged version of the file, but associate it with
         # tagged version 1.0.0 because the file was added before that
         # version.
@@ -647,8 +647,8 @@ class BasicTest(Base):
         self.c.override(
             earliest_version=None,
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -672,8 +672,8 @@ class BasicTest(Base):
         self.c.override(
             earliest_version=None,
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -698,8 +698,8 @@ class IgnoreTest(Base):
         self.c.override(
             ignore_notes=[f1],
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -717,8 +717,8 @@ class IgnoreTest(Base):
         self.c.override(
             ignore_notes=[os.path.basename(f1)],
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -736,8 +736,8 @@ class IgnoreTest(Base):
         self.c.override(
             ignore_notes=[scanner._get_unique_id(f1)],
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -758,8 +758,8 @@ class IgnoreTest(Base):
                 scanner._get_unique_id(f2),
             ],
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -775,8 +775,8 @@ class FileContentsTest(Base):
     def test_basic_file(self):
         # Prove that we can get a file we have committed.
         f1 = self._add_notes_file(contents='well-known-contents')
-        r = scanner.RenoRepo(self.reporoot)
-        contents = r.get_file_at_commit(f1, 'HEAD')
+        with scanner.RenoRepo(self.reporoot) as r:
+            contents = r.get_file_at_commit(f1, 'HEAD')
         self.assertEqual(
             b'well-known-contents',
             contents,
@@ -786,8 +786,8 @@ class FileContentsTest(Base):
         # Returns None when the file does not exist at all.
         # (we have to commit something, otherwise there is no HEAD)
         self._add_notes_file(contents='well-known-contents')
-        r = scanner.RenoRepo(self.reporoot)
-        contents = r.get_file_at_commit('no-such-dir/no-such-file', 'HEAD')
+        with scanner.RenoRepo(self.reporoot) as r:
+            contents = r.get_file_at_commit('no-such-dir/no-such-file', 'HEAD')
         self.assertEqual(
             None,
             contents,
@@ -799,8 +799,8 @@ class FileContentsTest(Base):
         with open(os.path.join(self.reporoot, f1), 'w') as f:
             f.write('new contents for file')
         self.repo.commit('edit note file')
-        r = scanner.RenoRepo(self.reporoot)
-        contents = r.get_file_at_commit(f1, 'HEAD')
+        with scanner.RenoRepo(self.reporoot) as r:
+            contents = r.get_file_at_commit(f1, 'HEAD')
         self.assertEqual(
             b'new contents for file',
             contents,
@@ -813,12 +813,11 @@ class FileContentsTest(Base):
         with open(os.path.join(self.reporoot, f1), 'w') as f:
             f.write('new contents for file')
         self.repo.commit('edit note file')
-        self.scanner = scanner.Scanner(self.c)
-        r = scanner.RenoRepo(self.reporoot)
-        head = r.head()
-        parent = r.get_parents(head)[0]
-        parent = parent.decode('ascii')
-        contents = r.get_file_at_commit(f1, parent)
+        with scanner.RenoRepo(self.reporoot) as r:
+            head = r.head()
+            parent = r.get_parents(head)[0]
+            parent = parent.decode('ascii')
+            contents = r.get_file_at_commit(f1, parent)
         self.assertEqual(
             b'initial-contents',
             contents,
@@ -830,8 +829,8 @@ class FileContentsTest(Base):
         f1 = self._add_notes_file(contents='initial-contents')
         with open(os.path.join(self.reporoot, f1), 'w') as f:
             f.write('new contents for file')
-        r = scanner.RenoRepo(self.reporoot)
-        contents = r.get_file_at_commit(f1, 'HEAD')
+        with scanner.RenoRepo(self.reporoot) as r:
+            contents = r.get_file_at_commit(f1, 'HEAD')
         self.assertEqual(
             b'initial-contents',
             contents,
@@ -843,8 +842,8 @@ class FileContentsTest(Base):
         f1 = self._add_notes_file(contents='initial-contents')
         with open(os.path.join(self.reporoot, f1), 'w') as f:
             f.write('new contents for file')
-        r = scanner.RenoRepo(self.reporoot)
-        contents = r.get_file_at_commit(f1, None)
+        with scanner.RenoRepo(self.reporoot) as r:
+            contents = r.get_file_at_commit(f1, None)
         self.assertEqual(
             'new contents for file',
             contents,
@@ -858,8 +857,8 @@ class PreReleaseTest(Base):
         self.repo.git('tag', '-s', '-m', 'first tag', '1.0.0.0a1')
         f1 = self._add_notes_file('slug1')
         self.repo.git('tag', '-s', '-m', 'first tag', '1.0.0.0a2')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -875,8 +874,8 @@ class PreReleaseTest(Base):
         self.repo.git('tag', '-s', '-m', 'first tag', '1.0.0.0b1')
         f1 = self._add_notes_file('slug1')
         self.repo.git('tag', '-s', '-m', 'first tag', '1.0.0.0b2')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -892,8 +891,8 @@ class PreReleaseTest(Base):
         self.repo.git('tag', '-s', '-m', 'first tag', '1.0.0.0rc1')
         f1 = self._add_notes_file('slug1')
         self.repo.git('tag', '-s', '-m', 'first tag', '1.0.0.0rc2')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -909,8 +908,8 @@ class PreReleaseTest(Base):
         self.repo.git('tag', '-s', '-m', 'first tag', 'v1.0.0.0a1')
         f1 = self._add_notes_file('slug1')
         self.repo.git('tag', '-s', '-m', 'first tag', 'v1.0.0.0a2')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -935,8 +934,8 @@ class PreReleaseTest(Base):
         self.c.override(
             collapse_pre_releases=True,
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -958,8 +957,8 @@ class PreReleaseTest(Base):
         self.c.override(
             collapse_pre_releases=True,
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -984,8 +983,8 @@ class PreReleaseTest(Base):
         self.c.override(
             collapse_pre_releases=True,
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -1015,8 +1014,8 @@ class MergeCommitTest(Base):
         time.sleep(0.1)  # force a delay between commits
         self.repo.add_file('ignore-2.txt')
         self.repo.git('tag', '-s', '-m', 'second tag', '2.0.0')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -1047,8 +1046,8 @@ class MergeCommitTest(Base):
         self.repo.git('show')
         self.repo.add_file('ignore-2.txt')
         self.repo.git('tag', '-s', '-m', 'second tag', '2.0.0')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -1081,8 +1080,8 @@ class MergeCommitTest(Base):
         self.repo.add_file('ignore-2.txt')
         self.repo.git('tag', '-s', '-m', 'third tag', '2.0.0')
         self.repo.add_file('ignore-3.txt')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -1119,8 +1118,8 @@ class MergeCommitTest(Base):
         self.repo.add_file('ignore-2.txt')
         self.repo.git('tag', '-s', '-m', 'third tag', '2.0.0')
         self.repo.add_file('ignore-3.txt')
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -1181,8 +1180,8 @@ class NullMergeTest(Base):
         # The scanner should skip over the null-merge and include the
         # notes that come before the version being merged in, up to
         # the base of the previous branch.
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -1200,8 +1199,8 @@ class NullMergeTest(Base):
         self.c.override(
             ignore_null_merges=False,
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -1245,6 +1244,10 @@ class BranchBaseTest(Base):
         self.repo.git('checkout', 'master')
         self.scanner = scanner.Scanner(self.c)
 
+    def tearDown(self):
+        self.scanner.close()
+        super().tearDown()
+
     def test_current_branch_no_extra_commits(self):
         # checkout the branch and then ask for its base
         self.repo.git('checkout', 'not-master')
@@ -1317,8 +1320,8 @@ class BranchTest(Base):
         f21 = self._add_notes_file('slug21')
         log_text = self.repo.git('log', '--decorate')
         self.addDetail('git log', text_content(log_text))
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -1342,8 +1345,8 @@ class BranchTest(Base):
         self.c.override(
             branch='stable/2',
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -1370,8 +1373,8 @@ class BranchTest(Base):
         self.c.override(
             stop_at_branch_base=False,
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -1407,8 +1410,8 @@ class BranchTest(Base):
             branch='stable/4',
             collapse_pre_releases=False,
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -1444,8 +1447,8 @@ class BranchTest(Base):
             branch='stable/4',
             collapse_pre_releases=True,
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -1482,8 +1485,8 @@ class BranchTest(Base):
             branch='stable/4',
             collapse_pre_releases=True,
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -1516,8 +1519,8 @@ class BranchTest(Base):
         self.c.override(
             branch='stable/4',
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -1550,8 +1553,8 @@ class BranchTest(Base):
         self.c.override(
             branch='stable/4',
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -1582,8 +1585,8 @@ class BranchTest(Base):
         self.c.override(
             branch='stable/4',
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -1599,8 +1602,8 @@ class BranchTest(Base):
         self.repo.git('checkout', '2.0.0')
         self.repo.git('checkout', '-b', 'stable/2')
         self.repo.git('checkout', 'master')
-        scanner1 = scanner.Scanner(self.c)
-        head1 = scanner1._get_ref('stable/2')
+        with scanner.Scanner(self.c) as scanner1:
+            head1 = scanner1._get_ref('stable/2')
         self.assertIsNotNone(head1)
         print('head1', head1)
         # Create a second repository by cloning the first.
@@ -1626,8 +1629,8 @@ class BranchTest(Base):
             cwd=reporoot2,
         ))
         c2 = config.Config(reporoot2)
-        scanner2 = scanner.Scanner(c2)
-        head2 = scanner2._get_ref('origin/stable/2')
+        with scanner.Scanner(c2) as scanner2:
+            head2 = scanner2._get_ref('origin/stable/2')
         self.assertIsNotNone(head2)
         self.assertEqual(head1, head2)
 
@@ -1635,8 +1638,8 @@ class BranchTest(Base):
         self.repo.git('checkout', '2.0.0')
         self.repo.git('checkout', '-b', 'stable/2')
         self.repo.git('checkout', 'master')
-        scanner1 = scanner.Scanner(self.c)
-        head1 = scanner1._get_ref('stable/2')
+        with scanner.Scanner(self.c) as scanner1:
+            head1 = scanner1._get_ref('stable/2')
         self.assertIsNotNone(head1)
         print('head1', head1)
         # Create a second repository by cloning the first.
@@ -1662,8 +1665,8 @@ class BranchTest(Base):
             cwd=reporoot2,
         ))
         c2 = config.Config(reporoot2)
-        scanner2 = scanner.Scanner(c2)
-        head2 = scanner2._get_ref('stable/2')
+        with scanner.Scanner(c2) as scanner2:
+            head2 = scanner2._get_ref('stable/2')
         self.assertIsNotNone(head2)
         self.assertEqual(head1, head2)
 
@@ -1680,8 +1683,8 @@ class BranchTest(Base):
         self.c.override(
             earliest_version=None,
         )
-        self.scanner = scanner.Scanner(self.c)
-        raw_results = self.scanner.get_notes_by_version()
+        with scanner.Scanner(self.c) as s:
+            raw_results = s.get_notes_by_version()
         results = {
             k: [f for (f, n) in v]
             for (k, v) in raw_results.items()
@@ -1720,6 +1723,10 @@ class ScanStopPointPrereleaseVersionsTest(Base):
         self.repo.git('tag', '-s', '-m', 'third tag', '2.0.0')
         self.repo.git('checkout', 'master')
 
+    def tearDown(self):
+        self.scanner.close()
+        super().tearDown()
+
     def test_beta_collapse(self):
         self.assertEqual(
             '1.0.0.0rc1',
@@ -1808,6 +1815,10 @@ class ScanStopPointRegularVersionsTest(Base):
         self.repo.git('tag', '-s', '-m', 'third tag', '2.0.2')
         self.repo.git('checkout', 'master')
 
+    def tearDown(self):
+        self.scanner.close()
+        super().tearDown()
+
     def test_invalid_earliest_version(self):
         self.assertIsNone(
             self.scanner._find_scan_stop_point(
@@ -1850,45 +1861,43 @@ class GetRefTest(Base):
         self.repo.git('tag', '-s', '-m', 'first tag', '1.0.0')
         self.repo.git('branch', 'stable/foo')
         self.repo.git('tag', 'bar-eol')
+        self.scanner = scanner.Scanner(self.c)
+
+    def tearDown(self):
+        self.scanner.close()
+        super().tearDown()
 
     def test_signed_tag(self):
-        self.scanner = scanner.Scanner(self.c)
         ref = self.scanner._get_ref('1.0.0')
         expected = self.scanner._repo.head()
         self.assertEqual(expected, ref)
 
     def test_unsigned_tag(self):
-        self.scanner = scanner.Scanner(self.c)
         ref = self.scanner._get_ref('bar-eol')
         expected = self.scanner._repo.head()
         self.assertEqual(expected, ref)
 
     def test_eol_tag_from_branch(self):
-        self.scanner = scanner.Scanner(self.c)
         ref = self.scanner._get_ref('stable/bar')
         expected = self.scanner._repo.head()
         self.assertEqual(expected, ref)
 
     def test_head(self):
-        self.scanner = scanner.Scanner(self.c)
         ref = self.scanner._get_ref(None)
         expected = self.scanner._repo.head()
         self.assertEqual(expected, ref)
 
     def test_stable_branch(self):
-        self.scanner = scanner.Scanner(self.c)
         ref = self.scanner._get_ref('stable/foo')
         expected = self.scanner._repo.head()
         self.assertEqual(expected, ref)
 
     def test_stable_branch_with_origin_prefix(self):
-        self.scanner = scanner.Scanner(self.c)
         ref = self.scanner._get_ref('origin/stable/foo')
         expected = self.scanner._repo.head()
         self.assertEqual(expected, ref)
 
     def test_no_such_value(self):
-        self.scanner = scanner.Scanner(self.c)
         self.assertRaises(
             ValueError,
             self.scanner._get_ref,
@@ -1909,17 +1918,17 @@ class TagsTest(Base):
         self.repo.git('tag', '-s', '-m', 'first tag', '3.0.0')
 
     def test_master(self):
-        self.scanner = scanner.Scanner(self.c)
-        results = self.scanner._get_tags_on_branch(None)
+        with scanner.Scanner(self.c) as s:
+            results = s._get_tags_on_branch(None)
         self.assertEqual(
             ['3.0.0', '2.0.0', '1.0.0'],
             results,
         )
 
     def test_get_ref(self):
-        self.scanner = scanner.Scanner(self.c)
-        ref = self.scanner._get_ref('3.0.0')
-        expected = self.scanner._repo.head()
+        with scanner.Scanner(self.c) as s:
+            ref = s._get_ref('3.0.0')
+            expected = s._repo.head()
         self.assertEqual(expected, ref)
 
     def test_not_master(self):
@@ -1928,8 +1937,8 @@ class TagsTest(Base):
         self._add_notes_file('slug4')
         self.repo.git('tag', '-s', '-m', 'not on master', '2.0.1')
         self.repo.git('checkout', 'master')
-        self.scanner = scanner.Scanner(self.c)
-        results = self.scanner._get_tags_on_branch('not-master')
+        with scanner.Scanner(self.c) as s:
+            results = s._get_tags_on_branch('not-master')
         self.assertEqual(
             ['2.0.1', '2.0.0', '1.0.0'],
             results,
@@ -1938,8 +1947,8 @@ class TagsTest(Base):
     def test_unsigned(self):
         self._add_notes_file('slug4')
         self.repo.git('tag', '-m', 'first tag', '4.0.0')
-        self.scanner = scanner.Scanner(self.c)
-        results = self.scanner._get_tags_on_branch(None)
+        with scanner.Scanner(self.c) as s:
+            results = s._get_tags_on_branch(None)
         self.assertEqual(
             ['4.0.0', '3.0.0', '2.0.0', '1.0.0'],
             results,
@@ -1948,8 +1957,8 @@ class TagsTest(Base):
     def test_tagged_tag_annotated(self):
         time.sleep(1)
         self.repo.git('tag', '-s', '-m', 'fourth tag', '4.0.0', '3.0.0')
-        self.scanner = scanner.Scanner(self.c)
-        results = self.scanner._get_tags_on_branch(None)
+        with scanner.Scanner(self.c) as s:
+            results = s._get_tags_on_branch(None)
         self.assertEqual(
             ['3.0.0', '4.0.0', '2.0.0', '1.0.0'],
             results,
@@ -1958,8 +1967,8 @@ class TagsTest(Base):
     def test_tagged_tag_lightweight(self):
         time.sleep(1)
         self.repo.git('tag', '-m', 'fourth tag', '4.0.0', '3.0.0')
-        self.scanner = scanner.Scanner(self.c)
-        results = self.scanner._get_tags_on_branch(None)
+        with scanner.Scanner(self.c) as s:
+            results = s._get_tags_on_branch(None)
         self.assertEqual(
             ['3.0.0', '4.0.0', '2.0.0', '1.0.0'],
             results,
@@ -1979,8 +1988,8 @@ class VersionTest(Base):
         self.repo.git('tag', '-s', '-m', 'third tag', '3.0.0')
 
     def test_tagged_head(self):
-        self.scanner = scanner.Scanner(self.c)
-        results = self.scanner._get_current_version(None)
+        with scanner.Scanner(self.c) as s:
+            results = s._get_current_version(None)
         self.assertEqual(
             '3.0.0',
             results,
@@ -1988,8 +1997,8 @@ class VersionTest(Base):
 
     def test_head_after_tag(self):
         self._add_notes_file('slug4')
-        self.scanner = scanner.Scanner(self.c)
-        results = self.scanner._get_current_version(None)
+        with scanner.Scanner(self.c) as s:
+            results = s._get_current_version(None)
         self.assertEqual(
             '3.0.0-1',
             results,
@@ -2002,8 +2011,8 @@ class VersionTest(Base):
         # single second (certainly not a person).
         time.sleep(1)
         self.repo.git('tag', '-s', '-m', 'fourth tag', '4.0.0')
-        self.scanner = scanner.Scanner(self.c)
-        results = self.scanner._get_current_version(None)
+        with scanner.Scanner(self.c) as s:
+            results = s._get_current_version(None)
         self.assertEqual(
             '4.0.0',
             results,
@@ -2452,11 +2461,9 @@ class GetSeriesBranchesTest(Base):
         self.repo.add_file('test.txt')
 
     def test_none(self):
-        self.scanner = scanner.Scanner(self.c)
-        self.assertEqual(
-            [],
-            self.scanner.get_series_branches(),
-        )
+        with scanner.Scanner(self.c) as s:
+            branches = s.get_series_branches()
+        self.assertEqual([], branches)
 
     def test_real_branches_sorted_names(self):
         self.repo.git(
@@ -2465,21 +2472,17 @@ class GetSeriesBranchesTest(Base):
         self.repo.git(
             'checkout', '-b', 'stable/b',
         )
-        self.scanner = scanner.Scanner(self.c)
-        self.assertEqual(
-            ['stable/a', 'stable/b'],
-            self.scanner.get_series_branches(),
-        )
+        with scanner.Scanner(self.c) as s:
+            branches = s.get_series_branches()
+        self.assertEqual(['stable/a', 'stable/b'], branches)
 
     def test_eol_tag(self):
         self.repo.git(
             'tag', '-s', '-m', 'closed branch', 'a-eol',
         )
-        self.scanner = scanner.Scanner(self.c)
-        self.assertEqual(
-            ['stable/a'],
-            self.scanner.get_series_branches(),
-        )
+        with scanner.Scanner(self.c) as s:
+            branches = s.get_series_branches()
+        self.assertEqual(['stable/a'], branches)
 
     def test_mix_tag_and_branch(self):
         self.repo.git(
@@ -2488,8 +2491,6 @@ class GetSeriesBranchesTest(Base):
         self.repo.git(
             'checkout', '-b', 'stable/b',
         )
-        self.scanner = scanner.Scanner(self.c)
-        self.assertEqual(
-            ['stable/a', 'stable/b'],
-            self.scanner.get_series_branches(),
-        )
+        with scanner.Scanner(self.c) as s:
+            branches = s.get_series_branches()
+        self.assertEqual(['stable/a', 'stable/b'], branches)