Fix detection of submodule remote versions

A new method get_submodule_versions_from_remote() is added
to the git module and used to detect the remote revisions
of the configured submodules.

The new method loops over the detected submodules and determines the
remote branch of each submodule as configured in the .gitmodules
file. The default remains "master".

lib/ansible/modules/git.py

@@ -569,6 +569,31 @@ def get_submodule_versions(git_path, module, dest, version='HEAD'):
     return submodules
 
 
+def get_submodule_config(git_path, module, dest, submodule_name, config_name):
+    config_path = 'submodule.' + submodule_name + '.' + config_name
+    cmd = [git_path, 'config', '-f', '.gitmodules', '--default', 'master', '--get', config_path]
+    (rc, out, err) = module.run_command(cmd, cwd=dest)
+    return out.rstrip('\n')
+
+
+def get_submodule_versions_from_remote(git_path, module, dest, submodule_revisions):
+    submodule_revisions_remote = {}
+    for submodule_name in submodule_revisions:
+        submodule_path = get_submodule_config(git_path, module, dest, submodule_name, 'path')
+        if not submodule_path:
+            module.fail_json(msg='Unable to detect path of submodule: %s' % submodule_name)
+
+        submodule_branch = get_submodule_config(git_path, module, dest, submodule_name, 'branch')
+        if not submodule_branch:
+            module.fail_json(msg='Unable to detect branch of submodule: %s' % submodule_name)
+
+        submodule_path = os.path.join(dest, submodule_path)
+        revision = get_version(module, git_path, submodule_path, '%s/%s' % ('origin', submodule_branch))
+        submodule_revisions_remote[submodule_name] = revision
+
+    return submodule_revisions_remote
+
+
 def clone(git_path, module, repo, dest, remote, depth, version, bare,
           reference, refspec, git_version_used, verify_commit, separate_git_dir, result, gpg_allowlist, single_branch):
     ''' makes a new git repo if it does not already exist '''
@@ -935,7 +960,7 @@ def fetch(git_path, module, repo, dest, version, remote, depth, bare, refspec, g
             module.fail_json(msg="Failed to %s: %s %s" % (label, out, err), cmd=command)
 
 
-def submodules_fetch(git_path, module, remote, track_submodules, dest):
+def submodules_fetch(git_path, module, track_submodules, dest):
     changed = False
 
     if not os.path.exists(os.path.join(dest, '.gitmodules')):
@@ -962,9 +987,7 @@ def submodules_fetch(git_path, module, remote, track_submodules, dest):
 
         if track_submodules:
             # Compare against submodule HEAD
-            # FIXME: determine this from .gitmodules
+            after = get_submodule_versions_from_remote(git_path, module, dest, begin)
-            version = 'master'
-            after = get_submodule_versions(git_path, module, dest, '%s/%s' % (remote, version))
             if begin != after:
                 changed = True
         else:
@@ -1393,7 +1416,7 @@ def main():
     # Deal with submodules
     submodules_updated = False
     if recursive and not bare:
-        submodules_updated = submodules_fetch(git_path, module, remote, track_submodules, dest)
+        submodules_updated = submodules_fetch(git_path, module, track_submodules, dest)
         if submodules_updated:
             result.update(submodules_changed=submodules_updated)