blurb: get BPO# from branch, add commit template - update the PR

blurb/blurb.py

@@ -76,7 +76,7 @@
 #
 # Please enter the relevant bugs.python.org issue number here:
 #
-.. bpo:
+.. bpo: {bpo}
 
 #
 # Uncomment one of these "section:" lines to specify which section
@@ -913,24 +913,12 @@ def add():
     os.close(handle)
     atexit.register(lambda : os.unlink(tmp_path))
 
-    def init_tmp_with_template():
-        with open(tmp_path, "wt", encoding="utf-8") as file:
-            # hack:
-            # my editor likes to strip trailing whitespace from lines.
-            # normally this is a good idea.  but in the case of the template
-            # it's unhelpful.
-            # so, manually ensure there's a space at the end of the bpo line.
-            text = template
-
-            bpo_line = ".. bpo:"
-            without_space = "\n" + bpo_line + "\n"
-            with_space = "\n" + bpo_line + " \n"
-            if without_space not in text:
-                sys.exit("Can't find BPO line to ensure there's a space on the end!")
-            text = text.replace(without_space, with_space)
-            file.write(text)
+    # See if the branch name incidates the BPO number
+    branch_bpo, branch_suffix = get_bpo_git_branch()
 
-    init_tmp_with_template()
+    with open(tmp_path, "wt", encoding="utf-8") as f:
+        text = template.format(bpo=branch_bpo)
+        f.write(text)
 
     # We need to be clever about EDITOR.
     # On the one hand, it might be a legitimate path to an
@@ -976,6 +964,17 @@ def init_tmp_with_template():
     path = blurb.save_next()
     git_add_files.append(path)
     flush_git_add_files()
+
+    # For convenience, write a preformatted commit template. You can tell git to
+    # use this template with "git config.template .git/blurb".
+    msgfile = os.path.join(root, '.git', 'blurb')
+    if os.path.isdir(os.path.dirname(msgfile)):
+        metadata, text = blurb[0]
+        with open(msgfile, 'wt', encoding="utf-8") as f:
+            f.write("bpo-{}: {}\n".format(metadata['bpo'], branch_suffix))
+            f.write("\n")
+            f.write(text)
+
     print("Ready for commit.")
 
 
@@ -1156,6 +1155,28 @@ def flush_git_rm_files():
         git_rm_files.clear()
 
 
+def get_bpo_git_branch():
+    """Try to detect bpo number from branch name
+
+    Supports:
+       bpo1234
+       bpo_1234
+       bpo-1234
+
+    returns: branch number, branch suffix
+    """
+    try:
+        p = subprocess.run(["git", "rev-parse", "--abbrev-ref", "HEAD"], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+        p.check_returncode()
+    except subprocess.CalledProcessError:
+        return '', ''
+    branch = p.stdout.decode('utf-8').strip()
+    mo = re.match("^bpo[-_]?(\d+)[-_]?(.*)", branch)
+    if mo is None:
+        return '', branch
+    return mo.group(1), mo.group(2)
+
+
 # @subcommand
 # def noop():
 #     "Do-nothing command.  Used for blurb smoke-testing."