werk: improve "werk pick"

 * if pre-commit hooks fail, the "werk pick" can now be continued
   with "git cherry-pick --continue"
 * if the sha given to "werk pick" isn't a werk, it will work like
   "git cherry-pick", but it doesn't support the same command line
   parameters.

Change-Id: I32ae2032b0ba8298706d537e33573f35065426d7

werk

@@ -874,30 +874,51 @@ def main_pick(args: argparse.Namespace) -> None:
 
 
 def werk_cherry_pick(commit_id: str, no_commit: bool) -> None:
+    # First get the werk_id
+    result = subprocess.run(
+        ["git", "diff-tree", "--no-commit-id", "--name-only", "-r", commit_id],
+        capture_output=True,
+        check=True,
+    )
+    werk_id = None
+    for line in result.stdout.splitlines():
+        filename = line.decode('utf-8')
+        if filename.startswith(".werks/") and filename[7:].isdigit():
+            werk_id = int(filename[7:])
+
+    if werk_id is not None:
+        if os.path.exists(str(werk_id)):
+            bail_out(f"Trying to pick werk {werk_id}, but werk already present. Aborted.")
+
     # Cherry-pick the commit in question from the other branch
-    os.system("git cherry-pick --no-commit '%s'" % commit_id)  # nosec
+    cmd = ["git", "cherry-pick"]
+    if no_commit:
+        cmd.append("--no-commit")
+    cmd.append(commit_id)
+    pick = subprocess.run(cmd, check=False)
+    if pick.returncode:
+        # Exit with the result of the pick. This may be a merge conflict, so
+        # other tools may need to know about this.
+        sys.exit(pick.returncode)
 
     # Find werks that have been cherry-picked and change their version
     # to our current version
     load_werks()  # might have changed
-    for line in os.popen("git status --porcelain"):  # nosec
-        # M  .werks/103
-        #  M werk
-        _status, filename = line.strip().split(None, 1)
-        if filename.startswith(".werks/") and filename[7].isdigit():
-            werk_id = int(filename[7:])
-            change_werk_version(werk_id, g_current_version)
-            sys.stdout.write("Changed version of werk %s to %s.\n" %
-                             (format_werk_id(werk_id), g_current_version))
 
     # Commit
-    if not no_commit:
-        os.system("git commit -C '%s'" % commit_id)  # nosec
-
-    else:
-        sys.stdout.write("We don't commit yet. Here is the status:\n")
-        sys.stdout.write("Please commit with git commit -C '%s'\n\n" % commit_id)
-        os.system("git status")
+    if werk_id is not None:
+        change_werk_version(werk_id, g_current_version)
+        sys.stdout.write("Changed version of werk %s to %s.\n" %
+                         (format_werk_id(werk_id), g_current_version))
+
+        # This allows for picking regular commits as well
+        if not no_commit:
+            subprocess.run(["git", "add", str(werk_id)], check=True)
+            subprocess.run(["git", "commit", "--no-edit", "--amend"], check=True)
+        else:
+            sys.stdout.write("We don't commit yet. Here is the status:\n")
+            sys.stdout.write("Please commit with git commit -C '%s'\n\n" % commit_id)
+            subprocess.run(["git", "status"], check=True)
 
 
 def get_werk_ids() -> List[int]: