scripts: Add a script to rebase branches from old modules into monorepo

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/919>

diff --git a/scripts/rebase-branch-from-old-module.py b/scripts/rebase-branch-from-old-module.py
new file mode 100755 (executable)
index 0000000..2e0dbc7
--- /dev/null
+++ b/scripts/rebase-branch-from-old-module.py
@@ -0,0 +1,220 @@
+#!/usr/bin/env python3
+
+from pathlib import Path as P
+from urllib.parse import urlparse
+from contextlib import contextmanager
+import os
+import re
+import sys
+
+import argparse
+import requests
+
+import subprocess
+
+import random
+import string
+
+URL = "https://gitlab.freedesktop.org/"
+PARSER = argparse.ArgumentParser(
+    description="`Rebase` a branch from an old GStreamer module onto the monorepo"
+)
+PARSER.add_argument("repo", help="The repo with the old module to use.")
+PARSER.add_argument("branch", help="The branch to rebase.")
+
+log_depth = []               # type: T.List[str]
+
+@contextmanager
+def nested(name=''):
+    global log_depth
+    log_depth.append(name)
+    try:
+        yield
+    finally:
+        log_depth.pop()
+
+def bold(text: str):
+    return f"\033[1m{text}\033[0m"
+
+def green(text: str):
+    return f"\033[1;32m{text}\033[0m"
+
+def red(text: str):
+    return f"\033[1;31m{text}\033[0m"
+
+def yellow(text: str):
+    return f"\033[1;33m{text}\033[0m"
+
+def fprint(msg, nested=True):
+    if log_depth:
+        prepend = log_depth[-1] + ' | ' if nested else ''
+    else:
+        prepend = ''
+
+    print(prepend + msg, end="")
+    sys.stdout.flush()
+
+
+class GstCherryPicker:
+    def __init__(self):
+
+        self.branch = None
+        self.repo = None
+        self.module = None
+
+        self.git_rename_limit = None
+
+    def check_clean(self):
+        try:
+            out = self.git("status", "--porcelain")
+            if out:
+                fprint("\n" + red('Git repository is not clean:') + "\n```\n" + out + "\n```\n")
+                sys.exit(1)
+
+        except Exception as e:
+            sys.exit(
+                f"Git repository is not clean. Clean it up before running ({e})")
+
+    def run(self):
+        assert self.branch
+        assert self.repo
+        self.check_clean()
+
+        try:
+            git_rename_limit = int(self.git("config", "merge.renameLimit"))
+        except subprocess.CalledProcessError:
+            git_rename_limit = 0
+        if int(git_rename_limit) < 999999:
+            self.git_rename_limit = git_rename_limit
+            fprint("-> Setting git rename limit to 999999 so we can properly cherry-pick between repos")
+            self.git("config", "merge.renameLimit", "999999")
+            fprint(f"{green(' OK')}\n", nested=False)
+
+        try:
+            self.rebase()
+        finally:
+            if self.git_rename_limit is not None:
+                self.git("config", "merge.renameLimit", str(self.git_rename_limit))
+
+    def rebase(self):
+        repo = urlparse(self.repo)
+
+        repo_path = P(repo.path)
+        self.module = module = repo_path.stem
+        remote_name = f"{module}-{repo_path.parent.name}"
+        fprint('Adding remotes...')
+        self.git("remote", "add", remote_name, self.repo, can_fail=True)
+        self.git("remote", "add", module, f"{URL}gstreamer/{module}.git",
+                can_fail=True)
+        fprint(f"{green(' OK')}\n", nested=False)
+
+        fprint(f'Fetching {remote_name}...')
+        self.git("fetch", remote_name,
+            interaction_message=f"fetching {remote_name} with:\n"
+            f"   `$ git fetch {remote_name}`")
+        fprint(f"{green(' OK')}\n", nested=False)
+
+        fprint(f'Fetching {module}...')
+        self.git("fetch", module,
+            interaction_message=f"fetching {module} with:\n"
+            f"   `$ git fetch {module}`")
+        fprint(f"{green(' OK')}\n", nested=False)
+
+        prevbranch = self.git("rev-parse", "--abbrev-ref", "HEAD").strip()
+        tmpbranchname = f"{remote_name}_{self.branch}"
+        fprint(f'Checking out branch {remote_name}/{self.branch} as {tmpbranchname}\n')
+        try:
+            self.git("checkout", f"{remote_name}/{self.branch}", "-b", tmpbranchname)
+            self.git("rebase", f"{module}/master",
+                interaction_message=f"Failed rebasing {remote_name}/{self.branch} on {module}/master with:\n"
+                f"   `$ git rebase {module}/master`")
+            self.cherry_pick(tmpbranchname)
+        except:
+            self.git("rebase", "--abort", can_fail=True)
+            self.git("checkout", prevbranch)
+            self.git("branch", "-D", tmpbranchname)
+            raise
+        fprint(f"{green(' OK')}\n", nested=False)
+
+    def cherry_pick(self, branch):
+        shas = self.git('log', '--format=format:%H', f'{self.module}/master..').strip()
+        fprint(f'Resetting on origin/main')
+        self.git("reset", "--hard", "origin/main")
+        fprint(f"{green(' OK')}\n", nested=False)
+
+        for sha in reversed(shas.split()):
+            fprint(f' - Cherry picking: {bold(sha)}\n')
+            self.git("cherry-pick", sha,
+                     interaction_message=f"cherry-picking {sha} onto {branch} with:\n  "
+                                        f" `$ git cherry-pick {sha}`"
+            )
+
+
+    def git(self, *args, can_fail=False, interaction_message=None, call=False):
+        retry = True
+        while retry:
+            retry = False
+            try:
+                if not call:
+                    try:
+                        return subprocess.check_output(["git"] + list(args),
+                                                    stdin=subprocess.DEVNULL,
+                                                    stderr=subprocess.STDOUT).decode()
+                    except:
+                        if not can_fail:
+                            fprint(f"\n\n{bold(red('ERROR'))}: `git {' '.join(args)}` failed" + "\n", nested=False)
+                        raise
+                else:
+                    subprocess.call(["git"] + list(args))
+                    return "All good"
+            except Exception as e:
+                if interaction_message:
+                    output = getattr(e, "output", b"")
+                    if output is not None:
+                        out = output.decode()
+                    else:
+                        out = "????"
+                    fprint(f"\n```"
+                          f"\n{out}\n"
+                          f"Entering a shell to fix:\n\n"
+                          f" {bold(interaction_message)}\n\n"
+                          f"You should then exit with the following codes:\n\n"
+                          f"  - {bold('`exit 0`')}: once you have fixed the problem and we can keep moving the \n"
+                          f"  - {bold('`exit 1`')}: {bold('retry')}: once you have let the repo in a state where cherry-picking the commit should be to retried\n"
+                          f"  - {bold('`exit 3`')}: stop the script and abandon moving your MRs\n"
+                          "\n```\n", nested=False)
+                    try:
+                        if os.name == 'nt':
+                            shell = os.environ.get(
+                                "COMSPEC", r"C:\WINDOWS\system32\cmd.exe")
+                        else:
+                            shell = os.environ.get(
+                                "SHELL", os.path.realpath("/bin/sh"))
+                        subprocess.check_call(shell)
+                    except subprocess.CalledProcessError as e:
+                        if e.returncode == 1:
+                            retry = True
+                            continue
+                        elif e.returncode == 3:
+                            sys.exit(3)
+                    except:
+                        # Result of subshell does not really matter
+                        pass
+
+                    return "User fixed it"
+
+                if can_fail:
+                    return "Failed but we do not care"
+
+                raise e
+
+
+def main():
+    picker = GstCherryPicker()
+    PARSER.parse_args(namespace=picker)
+    picker.run()
+
+
+if __name__ == '__main__':
+    main()
+