bitbake: b4-config: Add basic support for b4 contribution workflow

b4[1] is a very nice tool for mail-based contribution. A config[2] file
exists to set up a few defaults. We can use it to set the To recipients
to always add, in our case the mailing list.

This also adds a wrapper script that is called by b4 to figure out which
addresses to put as Cc recipients. Considering that patches to the doc/
directory also need to be sent to the yocto-docs mailing list, this
wrapper handles that. A limitation of the script (lsdiff actually) is
that it doesn't know how to handle empty files, but those should be
of rather rare occurrences.

Because we currently do not have anything to check for patch validity,
remove requirement for b4 prep --check to be run before sending a patch
series, via disable-needs-checking in prep-pre-flight-checks.

[1] https://pypi.org/project/b4/
[2] https://b4.docs.kernel.org/en/latest/config.html

(Bitbake rev: 8843860010c97cc10ff69205d209634639b6c5cd)

Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/.b4-config

@@ -0,0 +1,4 @@
+[b4]
+  send-series-to = bitbake-devel@lists.openembedded.org
+  send-auto-cc-cmd = ./contrib/b4-wrapper-bitbake.py send-auto-cc-cmd
+  prep-pre-flight-checks = disable-needs-checking

bitbake/contrib/b4-wrapper-bitbake.py

@@ -0,0 +1,40 @@
+#!/usr/bin/env python3
+#
+# Copyright OpenEmbedded Contributors
+#
+# SPDX-License-Identifier: MIT
+#
+# This script is to be called by b4:
+# - through b4.send-auto-cc-cmd with "send-auto-cc-cmd" as first argument,
+#
+# When send-auto-cc-cmd is passed:
+#
+#  This returns the list of Cc recipients for a patch.
+#
+# This script takes as stdin a patch.
+
+import subprocess
+import sys
+
+cmd = sys.argv[1]
+if cmd != "send-auto-cc-cmd":
+    sys.exit(-1)
+
+patch = sys.stdin.read()
+
+if subprocess.call(["which", "lsdiff"], stdout=subprocess.DEVNULL) != 0:
+    print("lsdiff missing from host, please install patchutils")
+    sys.exit(-1)
+
+files = subprocess.check_output(["lsdiff", "--strip-match=1", "--strip=1", "--include=doc/*"],
+                                input=patch, text=True)
+if len(files):
+    print("docs@lists.yoctoproject.org")
+else:
+# Handle patches made with --no-prefix
+    files = subprocess.check_output(["lsdiff", "--include=doc/*"],
+                                    input=patch, text=True)
+    if len(files):
+        print("docs@lists.yoctoproject.org")
+
+sys.exit(0)