[IMP] clone_oca_dependencies: Clone repositories from commits SHA (#619)

This improvement allows to clone repositories selecting a commit SHA.
Useful when you want to work with an specific state of the repository
that is not marked by any branch.

The syntax of the line you have to place in oca_dependencies.txt is as
follows:

```
server-tools [email protected]:OCA/server-tools.git 12.0 0c2c386

```

Note that you need to explicitly indicate a branch where the commit is
present because git doesn't allows to clone or fetch using directly a
commit SHA without having a configuration parameter set at server side[1].

So, when you choose to clone a repository using a commit SHA,
`clone_oca_dependencies` will fetch the commit history for the branch
you selected and then reset `HEAD` position to that commit.

[1] https://stackoverflow.com/questions/31278902/how-to-shallow-clone-a-specific-commit-with-depth-1/43136160#43136160

sample_files/oca_dependencies.txt

@@ -13,3 +13,7 @@
 #
 # To provide both the URL and a branch, use:
 # sale-workflow https://github.com/OCA/sale-workflow branchname
+#
+# To use a specific commit version, set the branch (required) and the
+# commit SHA to select:
+# sale-workflow https://github.com/OCA/sale-workflow branchname f848e37

travis/clone_oca_dependencies

@@ -21,7 +21,10 @@ The expected format for oca_dependencies.txt:
 * a dependency line contains:
   - the name of the OCA project
   - (optional) the URL to the git repository (defaulting to the OCA repository)
-  - (optional) the name of the branch to use (defaulting to ${VERSION})
+  - (optional) the name of the branch to use (defaulting to ${VERSION}). It is
+    required if you want to select a commit SHA in the next parameter.
+  - (optional) the commit SHA1 to use. If you set this option you MUST specify
+    the branch
 """
 from __future__ import print_function
 import sys
@@ -41,20 +44,18 @@ def parse_depfile(depfile, owner='OCA'):
         if not line or line.startswith('#'):
             continue
         parts = line.split()
-        repo = parts[0]
-        if len(parts) > 2:
-            branch = parts[2]
-        else:
+        num_parts = len(parts)
+        repo, url, branch, commit = [
+            num_parts > i and parts[i] for i in range(4)]
+        if not branch:
             branch = os.environ.get('VERSION', '8.0')
-        if len(parts) > 1:
-            url = parts[1]
-        else:
+        if not url:
             url = 'https://github.com/%s/%s.git' % (owner, repo)
-        deps.append((repo, url, branch))
+        deps.append((repo, url, branch, commit))
     return deps
 
 
-def git_checkout(deps_checkout_dir, reponame, url, branch):
+def git_checkout(deps_checkout_dir, reponame, url, branch, commit=False):
     checkout_dir = osp.join(deps_checkout_dir, reponame)
     if not osp.isdir(checkout_dir):
         command = ['git', 'clone', '-q', url, '-b', branch,
@@ -63,8 +64,19 @@ def git_checkout(deps_checkout_dir, reponame, url, branch):
         command = ['git', '--git-dir=' + os.path.join(checkout_dir, '.git'),
                    '--work-tree=' + checkout_dir, 'pull', '--ff-only',
                    url, branch]
+    if commit:
+        try:
+            command.remove('--depth=1')
+            command.remove('--ff-only')
+        except ValueError:
+            pass
     _logger.info('Calling %s', ' '.join(command))
     subprocess.check_call(command)
+    if commit:
+        command = ['git',  '--git-dir=' + os.path.join(checkout_dir, '.git'),
+                   '--work-tree=' + checkout_dir, 'reset', '--hard', commit]
+        _logger.info('Calling %s', ' '.join(command))
+        subprocess.check_call(command)
     return checkout_dir
 
 
@@ -90,13 +102,13 @@ def run(deps_checkout_dir, build_dir):
                 deps = parse_depfile(depfile)
         except IOError:
             deps = []
-        for depname, url, branch in deps:
+        for depname, url, branch, commit in deps:
             _logger.info('* processing %s', depname)
             if depname in processed:
                 continue
             processed.add(depname)
             checkout_dir = git_checkout(deps_checkout_dir, depname,
-                                        url, branch)
+                                        url, branch, commit)
             new_dep_filename = osp.join(checkout_dir, 'oca_dependencies.txt')
             reqfilename = osp.join(checkout_dir, 'requirements.txt')
             if osp.isfile(reqfilename):