[PATCH b4 2/3] shazam: enable three-way merge for b4 shazam -H

[Christian Brauner <brauner@kernel.org>]

Pass -3 to git-am so three-way merge is attempted automatically when
applying patches in the sparse worktree. Without this, even
auto-resolvable conflicts cause git-am to fail.

Also support a shazam-am-flags config option to allow users to pass
additional flags to git-am.

Co-developed-by: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 src/b4/mbox.py | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/b4/mbox.py b/src/b4/mbox.py
index 132cbb9..0a86f6f 100644
--- a/src/b4/mbox.py
+++ b/src/b4/mbox.py
@@ -383,12 +383,21 @@ def make_am(msgs: List[EmailMessage], cmdargs: argparse.Namespace, msgid: str) -
 
         base_commit = get_base_commit(topdir, first_body, lser, cmdargs)
         linkurl = linkmask % top_msgid
+
+        am_flags = ['-3']
+        amflags_cfg = str(config.get('shazam-am-flags', ''))
+        if amflags_cfg:
+            sp = shlex.shlex(amflags_cfg, posix=True)
+            sp.whitespace_split = True
+            am_flags.extend(list(sp))
+
         try:
             if cmdargs.mergebase:
                 logger.info(' Base: %s', base_commit)
             else:
                 logger.info(' Base: %s (use --merge-base to override)', base_commit)
-            b4.git_fetch_am_into_repo(topdir, ambytes=ambytes, at_base=base_commit, origin=linkurl)
+            b4.git_fetch_am_into_repo(topdir, ambytes=ambytes, at_base=base_commit,
+                                       origin=linkurl, am_flags=am_flags)
         except b4.AmConflictError as cex:
             b4.git_run_command(topdir, ['worktree', 'remove', '--force', cex.worktree_path])
             logger.critical('Unable to cleanly apply series, see failure log below')

-- 
2.47.3