Initial fixture for git library

Provide fixture object that can be used to build isolated test envs
when working with git and developing git tooling that uses the git
application.

Change-Id: I5b39f8d52beca848adb20d646c26d91c4b977b92

.stestr.conf

@@ -0,0 +1,3 @@
+[DEFAULT]
+test_path=tests
+top_dir=./

fixtures_git/__init__.py

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+# Copyright (c) 2013-2016 Hewlett-Packard Enterprise Development Company, L.P.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+import os
+import re
+import shutil
+import tempfile
+
+import fixtures
+import git
+import loremipsum
+
+
+__all__ = [
+    'GitFixture'
+]
+
+
+def _get_node_to_pick(node):
+    m = re.search(r'(.*)(\d+)$', node)
+    if m:
+        # get copy of a another change
+        node_number = int(m.group(2)) - 1
+        node_name = m.group(1)
+        if node_number > 0:
+            node_name += str(node_number)
+        return node_name
+    return None
+
+
+_NOT_VISITED = 0
+_VISITED = 1
+_FINISHED = 2
+
+
+def reverse_toposort(data):
+
+    # convert to dict for linear lookup times when returning
+    data = dict(data)
+
+    # keep track of nodes visited and processed
+    # by checking if a child has been visited before but not processed you
+    # can detect a back edge and abort since the graph is not acyclic
+    visited = dict()
+
+    # DFS algorithm with customization to handle use of '=' notation for merge
+    # commits and also the additional dependency for cherry-picking
+    nodes_to_visit = []
+    for i in data.keys():
+        if i not in visited:
+            nodes_to_visit.append(i)
+
+        while nodes_to_visit:
+            node = nodes_to_visit.pop()
+            if visited.get(node) is _VISITED:
+                # already visited so just return it with it's deps
+                yield (node, data[node])
+                visited[node] = _FINISHED
+                continue
+            elif visited.get(node) is _FINISHED:
+                continue
+
+            visited[node] = _VISITED
+            nodes_to_visit.append(node)
+            # special case for cherry-picking changes
+            c_node = _get_node_to_pick(node)
+            if c_node and c_node not in visited:
+                nodes_to_visit.append(c_node)
+
+            for d in data[node]:
+                r_d = d.strip('=')
+                if r_d not in visited:
+                    nodes_to_visit.append(r_d)
+                else:
+                    # if we've already visited a dep but not processed it,
+                    # then we have a back edge of some kind
+                    if visited[r_d] is _VISITED:
+                        message = ("Graph is not acyclic: %s is a dependency "
+                                   "of %s, but has been visited without being "
+                                   "processed before it." % (r_d, node))
+                        raise RuntimeError(message)
+
+
+class GitTree(object):
+
+    def __init__(self, gitrepo, tree, branches):
+        self.graph = {}
+        self.gitrepo = gitrepo
+        self.repo = gitrepo.repo
+        self._build_git_tree(tree, branches)
+
+    def _commit(self, node):
+        p_node = _get_node_to_pick(node)
+        if p_node:
+            self.repo.git.cherry_pick(self.graph[p_node], x=True)
+        else:
+            # standard commit
+            self.gitrepo.add_commits(1, ref="HEAD",
+                                     message_prefix="[%s]" % node)
+
+    def _merge_commit(self, node, parents):
+        # merge commits
+        parent_nodes = [p.lstrip("=") for p in parents]
+        commits = [str(self.graph[p]) for p in parent_nodes[1:]]
+
+        if any([p.startswith("=") for p in parents]):
+            # special merge commit using inverse of 'ours' by
+            # emptying the current index and then reading in any
+            # trees of the nodes prefixed with '='
+            use = [str(self.graph[p.lstrip("=")])
+                   for p in parents if p.startswith("=")]
+            try:
+                self.repo.git.merge(*commits, s="ours", no_commit=True)
+            except git.exc.GitCommandError as exc:
+                if 'refusing to merge unrelated histories' in exc.stderr:
+                    self.repo.git.merge(*commits, s="ours", no_commit=True,
+                                        allow_unrelated_histories=True)
+                else:
+                    raise
+            self.repo.git.read_tree(empty=True)
+            self.repo.git.read_tree(empty=True)
+            self.repo.git.read_tree(*use, u=True, reset=True)
+        elif len(commits) < 2:
+            # standard merge
+            try:
+                self.repo.git.merge(*commits, no_commit=True)
+            except git.exc.GitCommandError as exc:
+                if 'refusing to merge unrelated histories' in exc.stderr:
+                    self.repo.git.merge(*commits, no_commit=True,
+                                        allow_unrelated_histories=True)
+                else:
+                    raise
+        else:
+            # multi-branch merge, git is not great at handling
+            # merging multiple orphaned branches
+            try:
+                self.repo.git.merge(*commits, s="ours", no_commit=True)
+            except git.exc.GitCommandError as exc:
+                if 'refusing to merge unrelated histories' in exc.stderr:
+                    self.repo.git.merge(*commits, s="ours", no_commit=True,
+                                        allow_unrelated_histories=True)
+                else:
+                    raise
+            self.repo.git.read_tree(empty=True)
+            self.repo.git.read_tree("HEAD", *commits)
+            self.repo.git.checkout("--", ".")
+        self.repo.git.commit(m="[%s] Merging %s into %s" %
+                               (node, ",".join(parent_nodes[1:]),
+                                parent_nodes[0]))
+        self.repo.git.clean(f=True, d=True, x=True)
+
+    def _build_git_tree(self, graph_def, branches=[]):
+        """Helper function to build a git repository from a graph definition
+        of nodes and their parent nodes. A list of branches may be provided
+        where each element has two members corresponding to the name and the
+        target node it references.
+
+        Supports unordered graphs, only requirement is that there is a commit
+        defined with no parents, which will become the root commit.
+
+        Root commits can specified by an empty list as the second member:
+
+            ('NodeA', [])
+
+        Merge commits are specified by multiple nodes:
+
+            ('NodeMerge', ['Node1', 'Node2'])
+
+
+        As the import subcommand to git-upstream supports a special merge
+        commit that ignores all previous history from the other tree being
+        merged in using the 'ours' strategy. You specify this by defining
+        a parent node as '=<Node>'. The resulting merge commit contains just
+        the contents of the tree from the specified parent while still
+        recording the parents.
+
+        Following will result in a merge commit 'C', with parents 'P1' and
+        'P2', but will have the same tree as 'P1'.
+
+            ('C', ['=P1', 'P2'])
+
+
+        The tree building code can handle a graph definition being out of
+        order but will fail to find certain circular dependencies and may
+        result in an infinite loop.
+
+        Examples:
+
+            [('A', []), ('B', ['A']), ('C', ['B'])]
+            [('A', []), ('C', ['B']), ('B', ['A'])]
+        """
+
+        # require that graphs must have at least 1 node with no
+        # parents, which is a root commit in git
+        if not any([True for _, parents in graph_def if not parents]):
+            assert("No root commit defined in test graph")
+
+        for node, parents in reverse_toposort(graph_def):
+            if not parents:
+                # root commit
+                self.repo.git.symbolic_ref("HEAD", "refs/heads/%s" % node)
+                self.repo.git.rm(".", r=True, cached=True,
+                                 with_exceptions=False)
+                self.repo.git.clean(f=True, d=True, x=True)
+                self.gitrepo.add_commits(1, ref="HEAD",
+                                         message_prefix="[%s]" % node)
+                # only explicitly listed branches should exist afterwards
+                self.repo.git.checkout(self.repo.commit())
+                self.repo.git.branch(node, D=True)
+
+            else:
+                # checkout the dependent node
+                self.repo.git.checkout(self.graph[parents[0].lstrip('=')])
+                if len(parents) > 1:
+                    # merge commits
+                    self._merge_commit(node, parents)
+                else:
+                    self._commit(node)
+            self.graph[node] = self.repo.commit()
+
+        for name, node in branches:
+            self.repo.git.branch(name, str(self.graph[node]), f=True)
+
+        # return to master
+        self.repo.git.checkout("master")
+
+    def commits_from_nodes(self, nodes=[]):
+
+        return [self.graph[n] for n in nodes]
+
+
+class GitFixture(fixtures.Fixture):
+    """Create a git repo in which to operate.
+
+    By default creates an empty git repository under a temporary
+    directory and deletes it after use.
+
+    It accepts options to automatically define a git repository
+    layout based on list of commits setting the given branches to
+    the relevant node once built.
+
+    :ivar graph: Iterable describing the tree of git commits to create.
+    :ivar branches: Dict of node to branch names to set once finished.
+    :ivar path: Custom path to use, otherwise will create a temporary
+        directory to use and set the 'path' attribute to it.
+    :ivar user: Dict describing a user to use for commits, defaults
+        to 'Example User <user@example.com>',
+    :ivar clean_on_exit: Control whether to delete the tempoary path
+        once complete, defaults to 'True', but is ignored if 'path'
+        is provided.
+    """
+
+    def __init__(self, graph=None, branches=None, path=None, user=None,
+                 clean_on_exit=True):
+        # set attributes for use
+        self.path = path
+        self.gittree = None
+        self.repo = None
+
+        # internal attributes
+        self._graph = graph or []
+        self._branches = branches or []
+        self._user = {
+            'name': 'Example User',
+            'email': 'user@example.com',
+        }
+        self._user.update(user or {})
+
+        self._clean_on_exit = clean_on_exit
+
+    def _setUp(self):
+        self._file_list = set()
+        if not self.path:
+            tempdir = self.useFixture(fixtures.TempDir())
+            self.path = os.path.join(tempdir.path, 'git')
+            if self._clean_on_exit is True:
+                self.addCleanup(shutil.rmtree, tempdir.path)
+
+        os.mkdir(self.path)
+        g = git.Git(self.path)
+        g.init()
+
+        self.repo = git.Repo(self.path)
+        self.repo.git.config('user.email', self._user['email'])
+        self.repo.git.config('user.name', self._user['name'])
+        self.repo.git.commit(m="Initialize empty repo", allow_empty=True)
+
+        if self._graph:
+            self.gittree = GitTree(self, self._graph, self._branches)
+
+    def _create_file(self):
+        contents = "\n\n".join(loremipsum.get_paragraphs(3))
+
+        # always want to ensure the files added to the repo are unique no
+        # matter which branch they are added to, as otherwise there may
+        # be conflicts caused by replaying local changes and performing
+        # merges
+        while True:
+            tmpfile = tempfile.NamedTemporaryFile(
+                dir=self.repo.working_dir, delete=False)
+            if tmpfile.name not in self._file_list:
+                self._file_list.add(tmpfile.name)
+                break
+            # case where same filename in use on a different branch
+            tmpfile.close()
+            os.remove(tmpfile.name)
+
+        tmpfile.write(contents.encode('utf-8'))
+        tmpfile.close()
+        return tmpfile.name
+
+    def _create_file_commit(self, change_id=None, message_prefix=None):
+        filename = self._create_file()
+        self.repo.git.add(filename)
+        message = "Adding %s" % os.path.basename(filename)
+        if message_prefix:
+            message = "%s %s" % (message_prefix, message)
+        if change_id:
+            message = message + "\n\nChange-Id: %s" % change_id
+        self.repo.git.commit(m=message)
+
+    def add_commits(self, num=1, ref="HEAD", change_ids=[],
+                    message_prefix=None):
+        """Create the given number of commits using generated files"""
+        if ref != "HEAD":
+            self.repo.git.checkout(ref)
+
+        num = max(num, len(change_ids))
+        ids = list(change_ids) + [None] * (num - len(change_ids))
+
+        for x in range(num):
+            self._create_file_commit(
+                change_id=ids[x], message_prefix=message_prefix)

requirements.txt

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+fixtures
+GitPython
+loremipsum

test-requirements.txt

@@ -1 +1,5 @@
+flake8
+hacking
 sphinx
+stestr
+testtools

tests/simple/test_fixture.py

@@ -0,0 +1,34 @@
+# Copyright (c) 2014 Hewlett-Packard Development Company, L.P.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+import testtools
+
+import fixtures_git
+
+
+class TestBuildTree(testtools.TestCase):
+
+    def test_basic(self):
+        pass
+
+    def test_merge(self):
+        pass
+
+    def test_merge_and_replace(self):
+        pass
+
+    def test_merge_unrelated_history(self):
+        pass

tests/test_toposort.py

@@ -0,0 +1,37 @@
+# Copyright (c) 2014 Hewlett-Packard Development Company, L.P.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+import testtools
+
+import fixtures_git
+
+
+class TestResolve(testtools.TestCase):
+
+    def test_ordered(self):
+        pass
+
+    def test_unordered(self):
+        pass
+
+    def test_merge(self):
+        pass
+
+    def test_multiple_merges(self):
+        pass
+
+    def test_merge_unrelated_history(self):
+        pass

tox.ini

@@ -6,10 +6,25 @@ skip_missing_interpreters = True
 
 [testenv]
 usedevelop = True
+setenv =
+    LANG=en_US.UTF-8
+    PYTHONDONTWRITEBYTECODE=1
+    SUBUNIT_FORMATTER=tee testr_subunit_log
+    VIRTUAL_ENV={envdir}
+
 install_command = pip install -U {opts} {packages}
-deps = -r{toxinidir}/test-requirements.txt
+deps = -r{toxinidir}/requirements.txt
+       -r{toxinidir}/test-requirements.txt
 commands =
-    python setup.py test
+    stestr run --slowest {posargs}
+
+[testenv:pep8]
+commands = flake8
+
+[testenv:cover]
+commands =
+    python setup.py stestr --coverage --coverage-package-name=fixtures_git
+    coverage report
 
 [testenv:docs]
 commands =
@@ -17,3 +32,8 @@ commands =
 
 [testenv:venv]
 commands = {posargs}
+
+[flake8]
+ignore=H236,H40
+show-source = True
+exclude = .venv,.tox,dist,doc,build,*.egg