[PATCH] shazam: Add the --merge-base argument

[Palmer Dabbelt <palmer@rivosinc.com>]

I was just handling a patch set where the author used English to
describe the dependencies.  They hadn't yet been merged at the time the
patch set was posted so I don't think there's really any way to make
sure the computers always understand the base, this just lets me quickly
override the automatic merge base detection when I run into something
non-canonical.

Link: https://lore.kernel.org/all/20220913061817.22564-1-zong.li@sifive.com/
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
---
 b4/command.py |  2 ++
 b4/mbox.py    | 13 ++++++++-----
 man/b4.5.rst  |  2 ++
 3 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/b4/command.py b/b4/command.py
index b16043e..5bb674e 100644
--- a/b4/command.py
+++ b/b4/command.py
@@ -171,6 +171,8 @@ def cmd():
     sp_sh.add_argument('--guess-lookback', dest='guessdays', type=int, default=21,
                        help=('(use with -H or -M) When guessing base, go back this many days from the patch date '
                              '(default: 3 weeks)'))
+    sp_sh.add_argument('--merge-base', dest='mergebase', type=str, default=None,
+                       help=('(use with -H or -M) Force this base when merging'))
     sp_sh.set_defaults(func=cmd_shazam)
 
     # b4 pr
diff --git a/b4/mbox.py b/b4/mbox.py
index ff96a11..c1a0660 100644
--- a/b4/mbox.py
+++ b/b4/mbox.py
@@ -231,14 +231,17 @@ def make_am(msgs, cmdargs, msgid):
         logger.critical(' Link: %s', linkurl)
 
     base_commit = None
-    matches = re.search(r'base-commit: .*?([\da-f]+)', first_body, re.MULTILINE)
-    if matches:
-        base_commit = matches.groups()[0]
+    if cmdargs.mergebase is not None:
+        base_commit = cmdargs.mergebase
     else:
-        # Try a more relaxed search
-        matches = re.search(r'based on .*?([\da-f]{40})', first_body, re.MULTILINE)
+        matches = re.search(r'base-commit: .*?([\da-f]+)', first_body, re.MULTILINE)
         if matches:
             base_commit = matches.groups()[0]
+        else:
+            # Try a more relaxed search
+            matches = re.search(r'based on .*?([\da-f]{40})', first_body, re.MULTILINE)
+            if matches:
+                base_commit = matches.groups()[0]
 
     if not base_commit and topdir and cmdargs.guessbase:
         logger.critical(' Base: attempting to guess base-commit...')
diff --git a/man/b4.5.rst b/man/b4.5.rst
index 073f32a..e889542 100644
--- a/man/b4.5.rst
+++ b/man/b4.5.rst
@@ -226,6 +226,8 @@ options:
                         Attempt to merge series as if it were a pull request (execs git-merge)
   --guess-lookback GUESSDAYS
                         (use with -H or -M) When guessing base, go back this many days from the patch date (default: 3 weeks)
+  --merge-base COMMIT
+                        (use with -H or -M) Force this base when merging
 
 *Example*: b4 shazam -H 20200313231252.64999-1-keescook@chromium.org
 
-- 
2.38.0