Support empty incremental bundles

codearchiver/modules/git.py

@@ -2,6 +2,7 @@ import codearchiver.core
 import codearchiver.subprocess
 import datetime
 import functools
+import hashlib
 import logging
 import os.path
 import shutil
@@ -16,7 +17,7 @@ class GitIndex(codearchiver.core.Index):
 		codearchiver.core.IndexField(key = 'Based on bundle', required = False, repeatable = True),
 		codearchiver.core.IndexField(key = 'Ref', required = True, repeatable = True),
 		codearchiver.core.IndexField(key = 'Root commit', required = True, repeatable = True),
-		codearchiver.core.IndexField(key = 'Commit', required = True, repeatable = True),
+		codearchiver.core.IndexField(key = 'Commit', required = False, repeatable = True),
 	]
 
 
@@ -82,7 +83,21 @@ class Git(codearchiver.core.Module):
 						basedOnBundles[oldBundle] = True
 
 		_logger.info(f'Bundling into {bundle}')
-		codearchiver.subprocess.run_with_log(['git', 'bundle', 'create', '--progress', f'../{bundle}', '--stdin', '--reflog', '--all'], cwd = directory, input = ''.join(f'^{commit}\n' for commit in oldCommits).encode('ascii'))
+		status , _, stderr = codearchiver.subprocess.run_with_log(['git', 'bundle', 'create', '--progress', f'../{bundle}', '--stdin', '--reflog', '--all'], cwd = directory, input = ''.join(f'^{commit}\n' for commit in oldCommits).encode('ascii'), check = False)
+		if status == 128 and stderr == 'fatal: Refusing to create empty bundle.\n':
+			# Manually write an empty bundle instead
+			# Cf. Documentation/technical/bundle-format.txt and Documentation/technical/pack-format.txt in git's repository for details on the formats
+			_logger.info('Writing empty bundle directly instead')
+			with open(bundle, 'wb') as fp:
+				fp.write(b'# v2 git bundle\n')  # bundle signature
+				fp.write(b'\n')  # bundle end of prerequisites and refs
+				packdata = b'PACK'  # pack signature
+				packdata += b'\0\0\0\x02'  # pack version
+				packdata += b'\0\0\0\0'  # pack number of objects
+				fp.write(packdata)
+				fp.write(hashlib.sha1(packdata).digest())  # pack checksum trailer
+		elif status != 0:
+			raise RuntimeError(f'git bundle creation returned with non-zero exit status {status}.')
 
 		_logger.info(f'Removing clone')
 		shutil.rmtree(directory)