Docs
plain-models
plain
models
cli.py Raw LLM
import os
import subprocess
import sys
import time

import click

from plain.cli import register_cli
from plain.packages import packages_registry
from plain.runtime import settings
from plain.utils.text import Truncator

from . import migrations
from .backups.cli import cli as backups_cli
from .backups.cli import create_backup
from .db import OperationalError, db_connection
from .migrations.autodetector import MigrationAutodetector
from .migrations.executor import MigrationExecutor
from .migrations.loader import AmbiguityError, MigrationLoader
from .migrations.migration import Migration, SettingsTuple
from .migrations.optimizer import MigrationOptimizer
from .migrations.questioner import (
    InteractiveMigrationQuestioner,
    NonInteractiveMigrationQuestioner,
)
from .migrations.recorder import MigrationRecorder
from .migrations.state import ModelState, ProjectState
from .migrations.writer import MigrationWriter
from .registry import models_registry


@register_cli("models")
@click.group()
def cli():
    pass


cli.add_command(backups_cli)


@cli.command()
@click.argument("parameters", nargs=-1)
def db_shell(parameters):
    """Runs the command-line client for specified database, or the default database if none is provided."""
    try:
        db_connection.client.runshell(parameters)
    except FileNotFoundError:
        # Note that we're assuming the FileNotFoundError relates to the
        # command missing. It could be raised for some other reason, in
        # which case this error message would be inaccurate. Still, this
        # message catches the common case.
        click.secho(
            f"You appear not to have the {db_connection.client.executable_name!r} program installed or on your path.",
            fg="red",
            err=True,
        )
        sys.exit(1)
    except subprocess.CalledProcessError as e:
        click.secho(
            '"{}" returned non-zero exit status {}.'.format(
                " ".join(e.cmd),
                e.returncode,
            ),
            fg="red",
            err=True,
        )
        sys.exit(e.returncode)


@cli.command()
def db_wait():
    """Wait for the database to be ready"""
    attempts = 0
    while True:
        attempts += 1
        waiting_for = False

        try:
            db_connection.ensure_connection()
        except OperationalError:
            waiting_for = True

        if waiting_for:
            if attempts > 1:
                # After the first attempt, start printing them
                click.secho(
                    f"Waiting for database (attempt {attempts})",
                    fg="yellow",
                )
            time.sleep(1.5)
        else:
            click.secho("✔ Database ready", fg="green")
            break


@cli.command(name="list")
@click.argument("package_labels", nargs=-1)
@click.option(
    "--app-only",
    is_flag=True,
    help="Only show models from packages that start with 'app'.",
)
def list_models(package_labels, app_only):
    """List installed models."""

    packages = set(package_labels)

    for model in sorted(
        models_registry.get_models(),
        key=lambda m: (m._meta.package_label, m._meta.model_name),
    ):
        pkg = model._meta.package_label
        pkg_name = packages_registry.get_package_config(pkg).name
        if app_only and not pkg_name.startswith("app"):
            continue
        if packages and pkg not in packages:
            continue
        fields = ", ".join(f.name for f in model._meta.get_fields())
        click.echo(
            f"{click.style(pkg, fg='cyan')}.{click.style(model.__name__, fg='blue')}"
        )
        click.echo(f"  table: {model._meta.db_table}")
        click.echo(f"  fields: {fields}")
        click.echo(f"  package: {pkg_name}\n")


@register_cli("makemigrations")
@cli.command()
@click.argument("package_labels", nargs=-1)
@click.option(
    "--dry-run",
    is_flag=True,
    help="Just show what migrations would be made; don't actually write them.",
)
@click.option("--empty", is_flag=True, help="Create an empty migration.")
@click.option(
    "--noinput",
    "--no-input",
    "no_input",
    is_flag=True,
    help="Tells Plain to NOT prompt the user for input of any kind.",
)
@click.option("-n", "--name", help="Use this name for migration file(s).")
@click.option(
    "--check",
    is_flag=True,
    help="Exit with a non-zero status if model changes are missing migrations and don't actually write them.",
)
@click.option(
    "-v",
    "--verbosity",
    type=int,
    default=1,
    help="Verbosity level; 0=minimal output, 1=normal output, 2=verbose output, 3=very verbose output",
)
def makemigrations(package_labels, dry_run, empty, no_input, name, check, verbosity):
    """Creates new migration(s) for packages."""

    written_files = []
    interactive = not no_input
    migration_name = name
    check_changes = check

    def log(msg, level=1):
        if verbosity >= level:
            click.echo(msg)

    def write_migration_files(changes, update_previous_migration_paths=None):
        """Take a changes dict and write them out as migration files."""
        directory_created = {}
        for package_label, package_migrations in changes.items():
            log(
                click.style(f"Migrations for '{package_label}':", fg="cyan", bold=True),
                level=1,
            )
            for migration in package_migrations:
                writer = MigrationWriter(migration)
                migration_string = os.path.relpath(writer.path)
                log(f"  {click.style(migration_string, fg='yellow')}\n", level=1)
                for operation in migration.operations:
                    log(f"    - {operation.describe()}", level=1)

                if not dry_run:
                    migrations_directory = os.path.dirname(writer.path)
                    if not directory_created.get(package_label):
                        os.makedirs(migrations_directory, exist_ok=True)
                        init_path = os.path.join(migrations_directory, "__init__.py")
                        if not os.path.isfile(init_path):
                            open(init_path, "w").close()
                        directory_created[package_label] = True

                    migration_string = writer.as_string()
                    with open(writer.path, "w", encoding="utf-8") as fh:
                        fh.write(migration_string)
                        written_files.append(writer.path)

                    if update_previous_migration_paths:
                        prev_path = update_previous_migration_paths[package_label]
                        if writer.needs_manual_porting:
                            log(
                                click.style(
                                    f"Updated migration {migration_string} requires manual porting.\n"
                                    f"Previous migration {os.path.relpath(prev_path)} was kept and "
                                    f"must be deleted after porting functions manually.",
                                    fg="yellow",
                                ),
                                level=1,
                            )
                        else:
                            os.remove(prev_path)
                            log(f"Deleted {os.path.relpath(prev_path)}", level=1)
                elif verbosity >= 3:
                    log(
                        click.style(
                            f"Full migrations file '{writer.filename}':",
                            fg="cyan",
                            bold=True,
                        ),
                        level=3,
                    )
                    log(writer.as_string(), level=3)

    # Validate package labels
    package_labels = set(package_labels)
    has_bad_labels = False
    for package_label in package_labels:
        try:
            packages_registry.get_package_config(package_label)
        except LookupError as err:
            click.echo(str(err), err=True)
            has_bad_labels = True
    if has_bad_labels:
        sys.exit(2)

    # Load the current graph state
    loader = MigrationLoader(None, ignore_no_migrations=True)

    # Raise an error if any migrations are applied before their dependencies.
    # Only the default db_connection is supported.
    loader.check_consistent_history(db_connection)

    # Check for conflicts
    conflicts = loader.detect_conflicts()
    if package_labels:
        conflicts = {
            package_label: conflict
            for package_label, conflict in conflicts.items()
            if package_label in package_labels
        }

    if conflicts:
        name_str = "; ".join(
            "{} in {}".format(", ".join(names), package)
            for package, names in conflicts.items()
        )
        raise click.ClickException(
            f"Conflicting migrations detected; multiple leaf nodes in the "
            f"migration graph: ({name_str})."
        )

    # Set up questioner
    if interactive:
        questioner = InteractiveMigrationQuestioner(
            specified_packages=package_labels,
            dry_run=dry_run,
        )
    else:
        questioner = NonInteractiveMigrationQuestioner(
            specified_packages=package_labels,
            dry_run=dry_run,
            verbosity=verbosity,
        )

    # Set up autodetector
    autodetector = MigrationAutodetector(
        loader.project_state(),
        ProjectState.from_models_registry(models_registry),
        questioner,
    )

    # Handle empty migrations if requested
    if empty:
        if not package_labels:
            raise click.ClickException(
                "You must supply at least one package label when using --empty."
            )
        changes = {
            package: [Migration("custom", package)] for package in package_labels
        }
        changes = autodetector.arrange_for_graph(
            changes=changes,
            graph=loader.graph,
            migration_name=migration_name,
        )
        write_migration_files(changes)
        return

    # Detect changes
    changes = autodetector.changes(
        graph=loader.graph,
        trim_to_packages=package_labels or None,
        convert_packages=package_labels or None,
        migration_name=migration_name,
    )

    if not changes:
        log(
            "No changes detected"
            if not package_labels
            else f"No changes detected in {'package' if len(package_labels) == 1 else 'packages'} "
            f"'{', '.join(package_labels)}'",
            level=1,
        )
    else:
        if check_changes:
            sys.exit(1)

        write_migration_files(changes)


@register_cli("migrate")
@cli.command()
@click.argument("package_label", required=False)
@click.argument("migration_name", required=False)
@click.option(
    "--fake", is_flag=True, help="Mark migrations as run without actually running them."
)
@click.option(
    "--plan",
    is_flag=True,
    help="Shows a list of the migration actions that will be performed.",
)
@click.option(
    "--check",
    "check_unapplied",
    is_flag=True,
    help="Exits with a non-zero status if unapplied migrations exist and does not actually apply migrations.",
)
@click.option(
    "--backup/--no-backup",
    "backup",
    is_flag=True,
    default=None,
    help="Explicitly enable/disable pre-migration backups.",
)
@click.option(
    "--prune",
    is_flag=True,
    help="Delete nonexistent migrations from the plainmigrations table.",
)
@click.option(
    "--no-input",
    "--noinput",
    "no_input",
    is_flag=True,
    help="Tells Plain to NOT prompt the user for input of any kind.",
)
@click.option(
    "-v",
    "--verbosity",
    type=int,
    default=1,
    help="Verbosity level; 0=minimal output, 1=normal output, 2=verbose output, 3=very verbose output",
)
def migrate(
    package_label,
    migration_name,
    fake,
    plan,
    check_unapplied,
    backup,
    prune,
    no_input,
    verbosity,
):
    """Updates database schema. Manages both packages with migrations and those without."""

    def migration_progress_callback(action, migration=None, fake=False):
        if verbosity >= 1:
            if action == "apply_start":
                click.echo(f"  Applying {migration}...", nl=False)
            elif action == "apply_success":
                if fake:
                    click.echo(click.style(" FAKED", fg="green"))
                else:
                    click.echo(click.style(" OK", fg="green"))
            elif action == "render_start":
                click.echo("  Rendering model states...", nl=False)
            elif action == "render_success":
                click.echo(click.style(" DONE", fg="green"))

    def describe_operation(operation):
        """Return a string that describes a migration operation for --plan."""
        prefix = ""
        is_error = False
        if hasattr(operation, "code"):
            code = operation.code
            action = (code.__doc__ or "") if code else None
        elif hasattr(operation, "sql"):
            action = operation.sql
        else:
            action = ""
        if action is not None:
            action = str(action).replace("\n", "")
        if action:
            action = " -> " + action
        truncated = Truncator(action)
        return prefix + operation.describe() + truncated.chars(40), is_error

    # Get the database we're operating from
    # Hook for backends needing any database preparation
    db_connection.prepare_database()

    # Work out which packages have migrations and which do not
    executor = MigrationExecutor(db_connection, migration_progress_callback)

    # Raise an error if any migrations are applied before their dependencies.
    executor.loader.check_consistent_history(db_connection)

    # Before anything else, see if there's conflicting packages and drop out
    # hard if there are any
    conflicts = executor.loader.detect_conflicts()
    if conflicts:
        name_str = "; ".join(
            "{} in {}".format(", ".join(names), package)
            for package, names in conflicts.items()
        )
        raise click.ClickException(
            "Conflicting migrations detected; multiple leaf nodes in the "
            f"migration graph: ({name_str})."
        )

    # If they supplied command line arguments, work out what they mean.
    target_package_labels_only = True
    if package_label:
        try:
            packages_registry.get_package_config(package_label)
        except LookupError as err:
            raise click.ClickException(str(err))

        if package_label not in executor.loader.migrated_packages:
            raise click.ClickException(
                f"Package '{package_label}' does not have migrations."
            )

    if package_label and migration_name:
        try:
            migration = executor.loader.get_migration_by_prefix(
                package_label, migration_name
            )
        except AmbiguityError:
            raise click.ClickException(
                f"More than one migration matches '{migration_name}' in package '{package_label}'. "
                "Please be more specific."
            )
        except KeyError:
            raise click.ClickException(
                f"Cannot find a migration matching '{migration_name}' from package '{package_label}'."
            )
        target = (package_label, migration.name)
        if (
            target not in executor.loader.graph.nodes
            and target in executor.loader.replacements
        ):
            incomplete_migration = executor.loader.replacements[target]
            target = incomplete_migration.replaces[-1]
        targets = [target]
        target_package_labels_only = False
    elif package_label:
        targets = [
            key for key in executor.loader.graph.leaf_nodes() if key[0] == package_label
        ]
    else:
        targets = executor.loader.graph.leaf_nodes()

    if prune:
        if not package_label:
            raise click.ClickException(
                "Migrations can be pruned only when a package is specified."
            )
        if verbosity > 0:
            click.secho("Pruning migrations:", fg="cyan")
        to_prune = set(executor.loader.applied_migrations) - set(
            executor.loader.disk_migrations
        )
        squashed_migrations_with_deleted_replaced_migrations = [
            migration_key
            for migration_key, migration_obj in executor.loader.replacements.items()
            if any(replaced in to_prune for replaced in migration_obj.replaces)
        ]
        if squashed_migrations_with_deleted_replaced_migrations:
            click.echo(
                click.style(
                    "  Cannot use --prune because the following squashed "
                    "migrations have their 'replaces' attributes and may not "
                    "be recorded as applied:",
                    fg="yellow",
                )
            )
            for migration in squashed_migrations_with_deleted_replaced_migrations:
                package, name = migration
                click.echo(f"    {package}.{name}")
            click.echo(
                click.style(
                    "  Re-run `plain migrate` if they are not marked as "
                    "applied, and remove 'replaces' attributes in their "
                    "Migration classes.",
                    fg="yellow",
                )
            )
        else:
            to_prune = sorted(
                migration for migration in to_prune if migration[0] == package_label
            )
            if to_prune:
                for migration in to_prune:
                    package, name = migration
                    if verbosity > 0:
                        click.echo(
                            click.style(f"  Pruning {package}.{name}", fg="yellow"),
                            nl=False,
                        )
                    executor.recorder.record_unapplied(package, name)
                    if verbosity > 0:
                        click.echo(click.style(" OK", fg="green"))
            elif verbosity > 0:
                click.echo("  No migrations to prune.")

    migration_plan = executor.migration_plan(targets)

    if plan:
        click.secho("Planned operations:", fg="cyan")
        if not migration_plan:
            click.echo("  No planned migration operations.")
        else:
            for migration in migration_plan:
                click.secho(str(migration), fg="cyan")
                for operation in migration.operations:
                    message, is_error = describe_operation(operation)
                    if is_error:
                        click.secho("    " + message, fg="yellow")
                    else:
                        click.echo("    " + message)
        if check_unapplied:
            sys.exit(1)
        return

    if check_unapplied:
        if migration_plan:
            sys.exit(1)
        return

    if prune:
        return

    # Print some useful info
    if verbosity >= 1:
        click.secho("Operations to perform:", fg="cyan")

        if target_package_labels_only:
            click.secho(
                "  Apply all migrations: "
                + (", ".join(sorted({a for a, n in targets})) or "(none)"),
                fg="yellow",
            )
        else:
            click.secho(
                f"  Target specific migration: {targets[0][1]}, from {targets[0][0]}",
                fg="yellow",
            )

    pre_migrate_state = executor._create_project_state(with_applied_migrations=True)

    # sql = executor.loader.collect_sql(migration_plan)
    # pprint(sql)

    if migration_plan:
        if backup or (backup is None and settings.DEBUG):
            backup_name = f"migrate_{time.strftime('%Y%m%d_%H%M%S')}"
            click.secho(
                f"Creating backup before applying migrations: {backup_name}",
                bold=True,
            )
            # Can't use ctx.invoke because this is called by the test db creation currently,
            # which doesn't have a context.
            create_backup.callback(
                backup_name=backup_name,
                pg_dump=os.environ.get(
                    "PG_DUMP", "pg_dump"
                ),  # Have to pass this in manually
            )
            print()

        if verbosity >= 1:
            click.secho("Running migrations:", fg="cyan")

        post_migrate_state = executor.migrate(
            targets,
            plan=migration_plan,
            state=pre_migrate_state.clone(),
            fake=fake,
        )
        # post_migrate signals have access to all models. Ensure that all models
        # are reloaded in case any are delayed.
        post_migrate_state.clear_delayed_models_cache()
        post_migrate_packages = post_migrate_state.models_registry

        # Re-render models of real packages to include relationships now that
        # we've got a final state. This wouldn't be necessary if real packages
        # models were rendered with relationships in the first place.
        with post_migrate_packages.bulk_update():
            model_keys = []
            for model_state in post_migrate_packages.real_models:
                model_key = model_state.package_label, model_state.name_lower
                model_keys.append(model_key)
                post_migrate_packages.unregister_model(*model_key)
        post_migrate_packages.render_multiple(
            [
                ModelState.from_model(models_registry.get_model(*model))
                for model in model_keys
            ]
        )

    elif verbosity >= 1:
        click.echo("  No migrations to apply.")
        # If there's changes that aren't in migrations yet, tell them
        # how to fix it.
        autodetector = MigrationAutodetector(
            executor.loader.project_state(),
            ProjectState.from_models_registry(models_registry),
        )
        changes = autodetector.changes(graph=executor.loader.graph)
        if changes:
            click.echo(
                click.style(
                    f"  Your models in package(s): {', '.join(repr(package) for package in sorted(changes))} "
                    "have changes that are not yet reflected in a migration, and so won't be applied.",
                    fg="yellow",
                )
            )
            click.echo(
                click.style(
                    "  Run `plain makemigrations` to make new "
                    "migrations, and then re-run `plain migrate` to "
                    "apply them.",
                    fg="yellow",
                )
            )


@cli.command()
@click.argument("package_labels", nargs=-1)
@click.option(
    "--format",
    type=click.Choice(["list", "plan"]),
    default="list",
    help="Output format.",
)
@click.option(
    "-v",
    "--verbosity",
    type=int,
    default=1,
    help="Verbosity level; 0=minimal output, 1=normal output, 2=verbose output, 3=very verbose output",
)
def show_migrations(package_labels, format, verbosity):
    """Shows all available migrations for the current project"""

    def _validate_package_names(package_names):
        has_bad_names = False
        for package_name in package_names:
            try:
                packages_registry.get_package_config(package_name)
            except LookupError as err:
                click.echo(str(err), err=True)
                has_bad_names = True
        if has_bad_names:
            sys.exit(2)

    def show_list(db_connection, package_names):
        """
        Show a list of all migrations on the system, or only those of
        some named packages.
        """
        # Load migrations from disk/DB
        loader = MigrationLoader(db_connection, ignore_no_migrations=True)
        recorder = MigrationRecorder(db_connection)
        recorded_migrations = recorder.applied_migrations()

        graph = loader.graph
        # If we were passed a list of packages, validate it
        if package_names:
            _validate_package_names(package_names)
        # Otherwise, show all packages in alphabetic order
        else:
            package_names = sorted(loader.migrated_packages)
        # For each app, print its migrations in order from oldest (roots) to
        # newest (leaves).
        for package_name in package_names:
            click.secho(package_name, fg="cyan", bold=True)
            shown = set()
            for node in graph.leaf_nodes(package_name):
                for plan_node in graph.forwards_plan(node):
                    if plan_node not in shown and plan_node[0] == package_name:
                        # Give it a nice title if it's a squashed one
                        title = plan_node[1]
                        if graph.nodes[plan_node].replaces:
                            title += f" ({len(graph.nodes[plan_node].replaces)} squashed migrations)"
                        applied_migration = loader.applied_migrations.get(plan_node)
                        # Mark it as applied/unapplied
                        if applied_migration:
                            if plan_node in recorded_migrations:
                                output = f" [X] {title}"
                            else:
                                title += " Run `plain migrate` to finish recording."
                                output = f" [-] {title}"
                            if verbosity >= 2 and hasattr(applied_migration, "applied"):
                                output += f" (applied at {applied_migration.applied.strftime('%Y-%m-%d %H:%M:%S')})"
                            click.echo(output)
                        else:
                            click.echo(f" [ ] {title}")
                        shown.add(plan_node)
            # If we didn't print anything, then a small message
            if not shown:
                click.secho(" (no migrations)", fg="red")

        # Find recorded migrations that aren't in the graph (prunable)
        prunable_migrations = [
            migration
            for migration in recorded_migrations
            if (
                migration not in loader.disk_migrations
                and (not package_names or migration[0] in package_names)
            )
        ]

        if prunable_migrations:
            click.echo()
            click.secho(
                "Recorded migrations not in migration files (candidates for pruning):",
                fg="yellow",
                bold=True,
            )
            prunable_by_package = {}
            for migration in prunable_migrations:
                package, name = migration
                if package not in prunable_by_package:
                    prunable_by_package[package] = []
                prunable_by_package[package].append(name)

            for package in sorted(prunable_by_package.keys()):
                click.secho(f"  {package}:", fg="yellow")
                for name in sorted(prunable_by_package[package]):
                    click.echo(f"    - {name}")

    def show_plan(db_connection, package_names):
        """
        Show all known migrations (or only those of the specified package_names)
        in the order they will be applied.
        """
        # Load migrations from disk/DB
        loader = MigrationLoader(db_connection)
        graph = loader.graph
        if package_names:
            _validate_package_names(package_names)
            targets = [key for key in graph.leaf_nodes() if key[0] in package_names]
        else:
            targets = graph.leaf_nodes()
        plan = []
        seen = set()

        # Generate the plan
        for target in targets:
            for migration in graph.forwards_plan(target):
                if migration not in seen:
                    node = graph.node_map[migration]
                    plan.append(node)
                    seen.add(migration)

        # Output
        def print_deps(node):
            out = []
            for parent in sorted(node.parents):
                out.append(f"{parent.key[0]}.{parent.key[1]}")
            if out:
                return f" ... ({', '.join(out)})"
            return ""

        for node in plan:
            deps = ""
            if verbosity >= 2:
                deps = print_deps(node)
            if node.key in loader.applied_migrations:
                click.echo(f"[X]  {node.key[0]}.{node.key[1]}{deps}")
            else:
                click.echo(f"[ ]  {node.key[0]}.{node.key[1]}{deps}")
        if not plan:
            click.secho("(no migrations)", fg="red")

    # Get the database we're operating from

    if format == "plan":
        show_plan(db_connection, package_labels)
    else:
        show_list(db_connection, package_labels)


@cli.command()
@click.argument("package_label")
@click.argument("start_migration_name", required=False)
@click.argument("migration_name")
@click.option(
    "--no-optimize",
    is_flag=True,
    help="Do not try to optimize the squashed operations.",
)
@click.option(
    "--noinput",
    "--no-input",
    "no_input",
    is_flag=True,
    help="Tells Plain to NOT prompt the user for input of any kind.",
)
@click.option("--squashed-name", help="Sets the name of the new squashed migration.")
@click.option(
    "-v",
    "--verbosity",
    type=int,
    default=1,
    help="Verbosity level; 0=minimal output, 1=normal output, 2=verbose output, 3=very verbose output",
)
def squash_migrations(
    package_label,
    start_migration_name,
    migration_name,
    no_optimize,
    no_input,
    squashed_name,
    verbosity,
):
    """
    Squashes an existing set of migrations (from first until specified) into a single new one.
    """
    interactive = not no_input

    def find_migration(loader, package_label, name):
        try:
            return loader.get_migration_by_prefix(package_label, name)
        except AmbiguityError:
            raise click.ClickException(
                f"More than one migration matches '{name}' in package '{package_label}'. Please be more specific."
            )
        except KeyError:
            raise click.ClickException(
                f"Cannot find a migration matching '{name}' from package '{package_label}'."
            )

    # Validate package_label
    try:
        packages_registry.get_package_config(package_label)
    except LookupError as err:
        raise click.ClickException(str(err))

    # Load the current graph state, check the app and migration they asked for exists
    loader = MigrationLoader(db_connection)
    if package_label not in loader.migrated_packages:
        raise click.ClickException(
            f"Package '{package_label}' does not have migrations (so squashmigrations on it makes no sense)"
        )

    migration = find_migration(loader, package_label, migration_name)

    # Work out the list of predecessor migrations
    migrations_to_squash = [
        loader.get_migration(al, mn)
        for al, mn in loader.graph.forwards_plan(
            (migration.package_label, migration.name)
        )
        if al == migration.package_label
    ]

    if start_migration_name:
        start_migration = find_migration(loader, package_label, start_migration_name)
        start = loader.get_migration(
            start_migration.package_label, start_migration.name
        )
        try:
            start_index = migrations_to_squash.index(start)
            migrations_to_squash = migrations_to_squash[start_index:]
        except ValueError:
            raise click.ClickException(
                f"The migration '{start_migration}' cannot be found. Maybe it comes after "
                f"the migration '{migration}'?\n"
                f"Have a look at:\n"
                f"  plain models show-migrations {package_label}\n"
                f"to debug this issue."
            )

    # Tell them what we're doing and optionally ask if we should proceed
    if verbosity > 0 or interactive:
        click.secho("Will squash the following migrations:", fg="cyan", bold=True)
        for migration in migrations_to_squash:
            click.echo(f" - {migration.name}")

        if interactive:
            if not click.confirm("Do you wish to proceed?"):
                return

    # Load the operations from all those migrations and concat together,
    # along with collecting external dependencies and detecting double-squashing
    operations = []
    dependencies = set()
    # We need to take all dependencies from the first migration in the list
    # as it may be 0002 depending on 0001
    first_migration = True
    for smigration in migrations_to_squash:
        if smigration.replaces:
            raise click.ClickException(
                "You cannot squash squashed migrations! Please transition it to a "
                "normal migration first"
            )
        operations.extend(smigration.operations)
        for dependency in smigration.dependencies:
            if isinstance(dependency, SettingsTuple):
                dependencies.add(dependency)
            elif dependency[0] != smigration.package_label or first_migration:
                dependencies.add(dependency)
        first_migration = False

    if no_optimize:
        if verbosity > 0:
            click.secho("(Skipping optimization.)", fg="yellow")
        new_operations = operations
    else:
        if verbosity > 0:
            click.secho("Optimizing...", fg="cyan")

        optimizer = MigrationOptimizer()
        new_operations = optimizer.optimize(operations, migration.package_label)

        if verbosity > 0:
            if len(new_operations) == len(operations):
                click.echo("  No optimizations possible.")
            else:
                click.echo(
                    f"  Optimized from {len(operations)} operations to {len(new_operations)} operations."
                )

    # Work out the value of replaces (any squashed ones we're re-squashing)
    # need to feed their replaces into ours
    replaces = []
    for migration in migrations_to_squash:
        if migration.replaces:
            replaces.extend(migration.replaces)
        else:
            replaces.append((migration.package_label, migration.name))

    # Make a new migration with those operations
    subclass = type(
        "Migration",
        (migrations.Migration,),
        {
            "dependencies": dependencies,
            "operations": new_operations,
            "replaces": replaces,
        },
    )
    if start_migration_name:
        if squashed_name:
            # Use the name from --squashed-name
            prefix, _ = start_migration.name.split("_", 1)
            name = f"{prefix}_{squashed_name}"
        else:
            # Generate a name
            name = f"{start_migration.name}_squashed_{migration.name}"
        new_migration = subclass(name, package_label)
    else:
        name = f"0001_{'squashed_' + migration.name if not squashed_name else squashed_name}"
        new_migration = subclass(name, package_label)
        new_migration.initial = True

    # Write out the new migration file
    writer = MigrationWriter(new_migration)
    if os.path.exists(writer.path):
        raise click.ClickException(
            f"Migration {new_migration.name} already exists. Use a different name."
        )
    with open(writer.path, "w", encoding="utf-8") as fh:
        fh.write(writer.as_string())

    if verbosity > 0:
        click.secho(
            f"Created new squashed migration {writer.path}", fg="green", bold=True
        )
        click.echo(
            "  You should commit this migration but leave the old ones in place;\n"
            "  the new migration will be used for new installs. Once you are sure\n"
            "  all instances of the codebase have applied the migrations you squashed,\n"
            "  you can delete them."
        )
        if writer.needs_manual_porting:
            click.secho("Manual porting required", fg="yellow", bold=True)
            click.echo(
                "  Your migrations contained functions that must be manually copied over,\n"
                "  as we could not safely copy their implementation.\n"
                "  See the comment at the top of the squashed migration for details."
            )
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