2 files changed, 36 insertions, 11 deletions

diff --git a/project.py b/project.py
index fdbf9e4a..80b0cf8d 100644
--- a/project.py
+++ b/project.py
@@ -2311,6 +2311,27 @@ class Project(object):
     # Enable the extension!
     self.config.SetString('extensions.%s' % (key,), value)
 
+  def ResolveRemoteHead(self, name=None):
+    """Find out what the default branch (HEAD) points to.
+
+    Normally this points to refs/heads/master, but projects are moving to main.
+    Support whatever the server uses rather than hardcoding "master" ourselves.
+    """
+    if name is None:
+      name = self.remote.name
+
+    # The output will look like (NB: tabs are separators):
+    # ref: refs/heads/master    HEAD
+    # 5f6803b100bb3cd0f534e96e88c91373e8ed1c44  HEAD
+    output = self.bare_git.ls_remote('-q', '--symref', '--exit-code', name, 'HEAD')
+
+    for line in output.splitlines():
+      lhs, rhs = line.split('\t', 1)
+      if rhs == 'HEAD' and lhs.startswith('ref:'):
+        return lhs[4:].strip()
+
+    return None
+
   def _CheckForImmutableRevision(self):
     try:
       # if revision (sha or tag) is not present then following function
diff --git a/subcmds/init.py b/subcmds/init.py
index 41578076..5ba0d074 100644
--- a/subcmds/init.py
+++ b/subcmds/init.py
@@ -54,7 +54,8 @@ from the server and is installed in the .repo/ directory in the
 current working directory.
 
 The optional -b argument can be used to select the manifest branch
-to checkout and use.  If no branch is specified, master is assumed.
+to checkout and use.  If no branch is specified, the remote's default
+branch is used.
 
 The optional -m argument can be used to specify an alternate manifest
 to be used. If no manifest is specified, the manifest default.xml
@@ -215,24 +216,27 @@ to update the working directory files.
 
       m._InitGitDir(mirror_git=mirrored_manifest_git)
 
-      if opt.manifest_branch:
-        m.revisionExpr = opt.manifest_branch
-      else:
-        m.revisionExpr = 'refs/heads/master'
-    else:
-      if opt.manifest_branch:
-        m.revisionExpr = opt.manifest_branch
-      else:
-        m.PreSync()
-
     self._ConfigureDepth(opt)
 
+    # Set the remote URL before the remote branch as we might need it below.
     if opt.manifest_url:
       r = m.GetRemote(m.remote.name)
       r.url = opt.manifest_url
       r.ResetFetch()
       r.Save()
 
+    if opt.manifest_branch:
+      m.revisionExpr = opt.manifest_branch
+    else:
+      if is_new:
+        default_branch = m.ResolveRemoteHead()
+        if default_branch is None:
+          # If the remote doesn't have HEAD configured, default to master.
+          default_branch = 'refs/heads/master'
+        m.revisionExpr = default_branch
+      else:
+        m.PreSync()
+
     groups = re.split(r'[,\s]+', opt.groups)
     all_platforms = ['linux', 'darwin', 'windows']
     platformize = lambda x: 'platform-' + x