Add env() config binding with teleport() for CLI-to-worker config passing

A partial log_config (no "version" key) is deep-merged over uvicorn's
default config before our patching, so users pass only their
customizations, e.g. log_config={"loggers": {"myapp": {"level":
"DEBUG"}}}.  Previously such dicts crashed at startup: dictConfig
requires a version, and our root entry referenced a "default" handler
that might not exist; that reference is now only added when the handler
exists.  The stock default formatter is replaced only when untouched,
so an overlaid fmt survives.  Dicts with version and non-dict configs
behave as before.  Documented in the README logging section, with tests
under fastapi-vue/tests (each patched config validated through
dictConfig).

README.md

@@ -129,3 +129,5 @@ The installed application instead depends on the lightweight [fastapi_vue](https
 This keeps the development tooling where it belongs while leaving the distributed application as a normal, self-contained Python package.
 
 ℹ️ The version numbering between the runtime and setup packages is synchronized, and the setup script always bumps the version in `pyproject.toml` to ensure compatible updates.
+
+<img src="https://raw.githubusercontent.com/LeoVasanko/fastapi-vue-setup/main/docs/my-app.webp" alt="My App startup box and log items" width="500">

fastapi-vue/README.md

@@ -73,27 +73,59 @@ A single `reload` argument replaces Uvicorn's separate reload arguments and may
 
 A startup box with the app name, version and connect URL is printed before serving. Pass a `startup_box` template (`{name}`, `{version}`, `{listen}`, `{url}`, ...) to customize it, None to disable, or use `server.print_startup_box` on its own.
 
-Printed by `server.run("my_app.app:app", listen=["localhost:3100"])`:
+<img src="https://raw.githubusercontent.com/LeoVasanko/fastapi-vue-setup/main/docs/my-app.webp" alt="My App startup box and log items" width="500">
-
-```
-╭──────────────────────────────────────────╮
-│ My App 0.1.0 @ 127.0.0.1:3100 [::1]:3100 │
-│ http://localhost:3100                    │
-╰──────────────────────────────────────────╯
-```
-
-Logging is integrated as well: removes noisy uvicorn logging, replacing it with prettified log formatting, a colored access log and tracebacks rendered by [tracerite](https://pypi.org/project/tracerite/). Note that HTTP responses also include tracerite formatting when `FastAPI(debug=True)` is used.
 
 Other arguments are generally passed to `uvicorn.run`, although some like `log_config` receive our modifications.
 
-> As a deployment option, environment `FORWARDED_ALLOW_IPS` controls `X-Forwarded` trusted IPs (default: `127.0.0.1,::1` works for typical setups).
+### Logging and exceptions
 
-### Environment (fastapi_vue.env)
+Pretty logging is configured automatically across the host process and all workers, at INFO in development and WARNING in production, with emoji level prefixes, colored access logs, and tracebacks rendered by [tracerite](https://pypi.org/project/tracerite/). With `FastAPI(debug=True)`, **Internal Server Error** responses use tracerite formatting as well.
 
-We use environment variables to pass values between program components, from devserver script setting dev mode and telling backend and frontend URLs, to your CLI, which in turn runs the FastAPI app that may also need access to this information. The variables are prefixed by the current application name to avoid conflicts. The CLI entry point should set one like `os.environ["FASTAPI_VUE"] = "MY_APP"`, before using `server.run`
+Application code can simply use `logging.info()` through `logging.exception()`, or ordinary `logging.getLogger("myapp")` loggers, without setting up logging itself. Set any logger's level when part of the application should be quieter or more verbose, for example `log_config={"loggers": {"myapp": {"level": "DEBUG"}}}`, accepting additions and overrides using [Python's logging configuration schema](https://docs.python.org/3/library/logging.config.html#logging-config-dictschema).
 
-The following properties read the environment and return `None` when variables haven't been set:
+## Environment
 
-- `fastapi_vue.env.prefix` — the prefix itself
+Environment variables are used to pass values across process boundaries, where ordinary Python variables cannot be shared. We provide runtime passing mainly intended for dev environment passing into the main application CLI, as well as config passing intended for the CLI to pass things to FastAPI side.
-- `fastapi_vue.env.dev` — running in development mode, from e.g. `MY_APP_DEV=1`
+
-- `fastapi_vue.env.vite_url`, `fastapi_vue.env.backend_url` — URLs set by the devserver
+Set the application prefix before `server.run()`, at top of your CLI main:
+
+```python
+os.environ["FASTAPI_VUE"] = "MY_APP"
+```
+
+### Runtime environment
+
+```python
+from fastapi_vue import env
+
+env.prefix       # application prefix
+env.dev          # development mode (bool)
+env.vite_url     # frontend URL (dev)
+env.backend_url  # backend URL (dev)
+```
+
+The three prefixed variables are set by devserver script and can be read anywhere in your application. Unset values return `None`.
+
+### Teleportation
+
+Mainly intended for passing application config from CLI main to all FastAPI workers and through reloader. Put shared configuration in its own module so that any part of your application can import the same `config` variable:
+
+```python
+from dataclasses import dataclass
+from fastapi_vue import env
+
+@dataclass
+class Config:
+    project: str = "."
+    read_only: bool = False
+
+config = env(Config)
+```
+
+The config values should be set (in CLI main) before teleportation, which occurs in `server.run()` for all registered env objects. Then everyone who imports the object receives those values. Modifications after that point however do not transit to other workers.
+
+Initially the passed in dataclass or msgspec.Struct is constructed with default values to its fields. Any number of env definitions may be added for different things, each getting a prefixed env variable by type name like `MY_APP_CONFIG` above. Beside `server.run`, pass objects to your own processes with `fastapi_vue.teleport()` if needed e.g. from FastAPI app to its workers. The data format in these variables is a JSON object.
+
+### Proxy configuration
+
+You may set `FORWARDED_ALLOW_IPS` to specify which connecting IP addresses are trusted to provide `X-Forwarded-*` headers. This is a server setup option rather than an application setting: the devserver does not set it, and it does not use the application-name prefix. It may therefore be set globally for the whole server. The default `127.0.0.1,::1` works for typical setups where Caddy, Nginx or another frontend server runs on the same machine.

fastapi-vue/fastapi_vue/__init__.py

@@ -1,6 +1,6 @@
 """FastAPI Vue integration - serve Vue frontend from FastAPI."""
 
-from .environ import env
+from .environ import env, teleport
 from .staticfiles import Frontend
 
-__all__ = ["Frontend", "env"]
+__all__ = ["Frontend", "env", "teleport"]

fastapi-vue/fastapi_vue/environ.py

@@ -4,12 +4,48 @@ The project entry point (generated __main__.py) sets FASTAPI_VUE to the
 project-specific prefix (e.g. "MY_APP"). Project settings are then passed
 as "<PREFIX>_*" environment variables; this module is the single place
 that resolves those names.
+
+Call env with a dataclass or msgspec.Struct type to bind an object of
+that type, e.g. env(Config). It is decoded from "<PREFIX>_<CLASS NAME>"
+when set (in spawned server processes) and default-constructed otherwise
+(in the CLI entry point, which mutates it before server.run() calls
+teleport()).
 """
 
+import dataclasses
+import json
 import os
+import re
+from typing import Any, TypeVar
 
 PREFIX_VARIABLE = "FASTAPI_VUE"
 
+# Names already used by fastapi-vue itself; bindings may not take them
+RESERVED_NAMES = frozenset({"DEV", "VITE_URL", "BACKEND_URL"})
+
+T = TypeVar("T")
+
+
+def _mangle(name: str) -> str:
+    """Class name to env name: underscores normalized, uppercased."""
+    return re.sub(r"_+", "_", name).strip("_").upper()
+
+
+def _encode(obj: Any) -> str:  # noqa: ANN401
+    if hasattr(type(obj), "__struct_fields__"):
+        import msgspec  # noqa: PLC0415
+
+        return msgspec.json.encode(obj).decode()
+    return json.dumps(dataclasses.asdict(obj))
+
+
+def _decode(raw: str, type_: type[T]) -> T:
+    if hasattr(type_, "__struct_fields__"):
+        import msgspec  # noqa: PLC0415
+
+        return msgspec.json.decode(raw, type=type_)
+    return type_(**json.loads(raw))
+
 
 class _Env:
     """Lazy accessors for the project's "<PREFIX>_*" environment variables.
@@ -18,6 +54,37 @@ class _Env:
     or the variable itself is not set.
     """
 
+    def __init__(self) -> None:
+        self._bindings: dict[str, tuple[type, Any]] = {}
+
+    def __call__(self, type_: type[T], *, name: str | None = None) -> T:
+        """Bind and return an object of the given type.
+
+        The type must be a dataclass or msgspec.Struct with defaults for
+        all fields. Decoded from the "<PREFIX>_<NAME>" variable when set,
+        default-constructed otherwise. The variable name is derived from
+        the class name unless overridden with name=. Repeated calls with
+        the same type return the same object; conflicting names raise
+        KeyError.
+        """
+        var = name if name is not None else _mangle(type_.__name__)
+        if var in RESERVED_NAMES:
+            msg = f"{var} is reserved for fastapi-vue itself"
+            raise KeyError(msg)
+        if bound := self._bindings.get(var):
+            bound_type, obj = bound
+            if bound_type is not type_:
+                msg = f"{var} is already bound to {bound_type}"
+                raise KeyError(msg)
+            return obj
+        if not (hasattr(type_, "__struct_fields__") or dataclasses.is_dataclass(type_)):
+            msg = f"{type_} must be a dataclass or msgspec.Struct"
+            raise TypeError(msg)
+        raw = self._get(var)
+        obj = _decode(raw, type_) if raw else type_()
+        self._bindings[var] = (type_, obj)
+        return obj
+
     @property
     def prefix(self) -> str | None:
         """Return the project prefix from the FASTAPI_VUE environment variable."""
@@ -44,3 +111,19 @@ class _Env:
 
 
 env = _Env()
+
+
+def teleport() -> None:
+    """Serialize objects bound via env() into environment variables.
+
+    Called by server.run() before spawning workers, so mutations made in
+    the CLI entry point propagate to them. Call directly only when spawning
+    server processes by other means.
+    """
+    if not env._bindings:  # noqa: SLF001
+        return
+    if not (prefix := env.prefix):
+        msg = f"{PREFIX_VARIABLE} is not set; cannot teleport bound objects"
+        raise RuntimeError(msg)
+    for var, (_, obj) in env._bindings.items():  # noqa: SLF001
+        os.environ[f"{prefix}_{var}"] = _encode(obj)

fastapi-vue/fastapi_vue/logging.py

@@ -20,7 +20,7 @@ from typing import TYPE_CHECKING, Literal
 import tracerite
 from starlette.middleware.errors import ServerErrorMiddleware
 from starlette.responses import HTMLResponse, JSONResponse, PlainTextResponse, Response
-from uvicorn.config import Config
+from uvicorn.config import LOGGING_CONFIG, Config
 from uvicorn.lifespan.on import LifespanOn
 
 if TYPE_CHECKING:
@@ -31,6 +31,7 @@ if TYPE_CHECKING:
     from uvicorn.lifespan.on import LifespanSendMessage
 
 from .accesslog import AccessLogMiddleware
+from .environ import env
 
 ANSI_ESCAPE_RE = re.compile(r"\x1b\[[0-9;]*m")
 
@@ -298,13 +299,25 @@ def patch_server_error_middleware() -> None:
     ServerErrorMiddleware.error_response = error_response  # type: ignore[method-assign]
 
 
+def _merge_log_config(base: dict, overlay: dict) -> dict:
+    """Deep-merge *overlay* onto *base*; dicts merge recursively, others replace."""
+    for key, value in overlay.items():
+        if isinstance(value, dict) and isinstance(base.get(key), dict):
+            _merge_log_config(base[key], value)
+        else:
+            base[key] = value
+    return base
+
+
 def patch_log_config(log_config, *, access_log: bool = True):  # noqa: ANN001, ANN201
     """Patch a uvicorn log_config dict for our logging, best-effort.
 
-    Users presumably base their config on uvicorn's default dict, but any
+    A dict without a ``version`` key is treated as a partial config: it is
-    shape is tolerated: pieces that do not fit the config's structure are
+    merged over uvicorn's default dict, so only the customizations are
-    silently skipped.  Non-dict configs (e.g. an ini file path) pass through
+    needed (e.g. ``{"loggers": {"kanta": {"level": "DEBUG"}}}``).  A dict
-    untouched.
+    with ``version`` is a complete config used as-is; pieces that do not
+    fit its structure are silently skipped.  Non-dict configs (e.g. an ini
+    file path) pass through untouched.
 
     Always adds an unreferenced NullHandler whose Formatter instantiation
     loads tracerite in every process uvicorn applies the config in, filters
@@ -312,7 +325,8 @@ def patch_log_config(log_config, *, access_log: bool = True):  # noqa: ANN001, A
     routine INFO lines, an emoji-level-prefix Formatter in place of
     uvicorn's stock ``default`` formatter (a user-supplied one wins), a root
     logger entry so ``logging.info()`` et al. print through the default
-    handler, and a no-prefix ``kanta`` logger entry (likewise).  The
+    handler when one exists, at INFO in dev and WARNING in production
+    (matching Python's default).  The
     ``watchfiles.main`` logger is lifted to WARNING so its INFO "N changes
     detected" line is dropped while the WARNING "Reloading..." line (logged
     to ``uvicorn.error``) still shows; a user-supplied level wins.
@@ -325,6 +339,8 @@ def patch_log_config(log_config, *, access_log: bool = True):  # noqa: ANN001, A
     if not isinstance(log_config, dict):
         return log_config
     config = deepcopy(log_config)
+    if "version" not in config:
+        config = _merge_log_config(deepcopy(LOGGING_CONFIG), config)
 
     with suppress(Exception):
         config["formatters"]["fastapi_vue"] = {"()": "fastapi_vue.logging.Formatter"}
@@ -346,7 +362,7 @@ def patch_log_config(log_config, *, access_log: bool = True):  # noqa: ANN001, A
     # default formatter; a user-supplied default formatter is left alone.
     with suppress(Exception):
         default = config["formatters"]["default"]
-        if default.get("()") in (None, "uvicorn.logging.DefaultFormatter"):
+        if default == LOGGING_CONFIG["formatters"]["default"]:
             config["formatters"]["default"] = {
                 "()": "fastapi_vue.logging.Formatter",
                 "fmt": "%(message)s",
@@ -355,9 +371,12 @@ def patch_log_config(log_config, *, access_log: bool = True):  # noqa: ANN001, A
 
     # uvicorn's default config leaves the root logger handlerless, eating
     # logging.info() et al.; route root through uvicorn's default handler.
+    # Level is WARNING in production so third-party loggers stay quiet, as
+    # with Python's default; dev keeps INFO.  Subloggers can override.
     with suppress(Exception):
         root = config.setdefault("root", {})
-        root.setdefault("level", "INFO")
+        root.setdefault("level", "INFO" if env.dev else "WARNING")
+        if "default" in config.get("handlers", {}):
             root_handlers = root.setdefault("handlers", [])
             if "default" not in root_handlers:
                 root_handlers.append("default")
@@ -369,23 +388,6 @@ def patch_log_config(log_config, *, access_log: bool = True):  # noqa: ANN001, A
             "level", "WARNING"
         )
 
-    # kanta-style output (diffs, colored headers) prints without prefixes,
-    # like our access log.  A user-supplied "kanta" logger entry wins.
-    with suppress(Exception):
-        config["formatters"].setdefault("plain", {"fmt": "%(message)s"})
-        config["handlers"].setdefault(
-            "plain",
-            {
-                "class": "logging.StreamHandler",
-                "formatter": "plain",
-                "stream": "ext://sys.stderr",
-            },
-        )
-        config.setdefault("loggers", {}).setdefault(
-            "kanta",
-            {"handlers": ["plain"], "level": "INFO", "propagate": False},
-        )
-
     if access_log:
         with suppress(Exception):
             config["formatters"]["access"] = {

fastapi-vue/fastapi_vue/server.py

@@ -15,7 +15,7 @@ from uvicorn import Config, Server
 from uvicorn.main import STARTUP_FAILURE
 from uvicorn.supervisors import ChangeReload, Multiprocess
 
-from .environ import env
+from .environ import env, teleport
 from .hostutil import parse_endpoints
 from .logging import (
     install_access_log,
@@ -148,6 +148,8 @@ def run(  # noqa: PLR0913
         msg = "No endpoints to serve; check listen configuration"
         raise ValueError(msg)
 
+    teleport()  # Serialize bound objects before spawning workers
+
     if startup_box:
         print_startup_box(startup_box, app, endpoints)
 

fastapi-vue/fastapi_vue/staticfiles.py

@@ -21,7 +21,7 @@ from zstandard import ZstdCompressor
 
 from .environ import env
 
-logger = logging.getLogger("uvicorn.error")  # Use FastAPI logging style
+logger = logging.getLogger(__name__)
 
 __all__ = ["Frontend"]
 

fastapi-vue/pyproject.toml

@@ -23,3 +23,8 @@ build-backend = "hatchling.build"
 [tool.hatch.version]
 source = "vcs"
 raw-options.root = ".."
+
+[dependency-groups]
+dev = [
+    "msgspec>=0.21.1",
+]

fastapi-vue/tests/__init__.py

@@ -0,0 +1 @@
+"""Tests for the fastapi_vue package."""

fastapi-vue/tests/test_environ.py

@@ -0,0 +1,126 @@
+"""Tests for env() object binding and teleport()."""
+
+import dataclasses
+import json
+import os
+from collections.abc import Iterator
+
+import msgspec
+import pytest
+from fastapi_vue import env, teleport
+from fastapi_vue.environ import PREFIX_VARIABLE, _Env
+
+
+@pytest.fixture(autouse=True)
+def _clean_bindings(monkeypatch: pytest.MonkeyPatch) -> Iterator[None]:
+    env._bindings.clear()  # noqa: SLF001
+    monkeypatch.setenv(PREFIX_VARIABLE, "TEST")
+    yield
+    env._bindings.clear()  # noqa: SLF001
+
+
+class StructConfig(msgspec.Struct):
+    """msgspec struct config."""
+
+    host: str = "localhost"
+    port: int = 8000
+
+
+@dataclasses.dataclass
+class DataclassConfig:
+    """Dataclass config."""
+
+    host: str = "localhost"
+    port: int = 8000
+
+
+def test_default_construction_and_identity() -> None:
+    """Unset env: default-constructed; repeated binds return the same object."""
+    config = env(StructConfig)
+    assert config.host == "localhost"
+    assert env(StructConfig) is config
+
+
+def test_name_mangling() -> None:
+    """Class names uppercase as-is; repeated/edge underscores normalize."""
+    env(StructConfig)
+    teleport()
+    assert json.loads(os.environ["TEST_STRUCTCONFIG"])["port"] == 8000
+
+    @dataclasses.dataclass
+    class _my__config_:  # noqa: N801
+        x: int = 0
+
+    env(_my__config_)
+    teleport()
+    assert "TEST_MY_CONFIG" in os.environ
+
+
+def test_name_override() -> None:
+    """name= overrides the mangled class name verbatim."""
+    env(DataclassConfig, name="SETTINGS")
+    teleport()
+    assert "TEST_SETTINGS" in os.environ
+
+
+def test_name_conflict() -> None:
+    """A different type with a colliding env name raises KeyError."""
+    env(StructConfig)
+    with pytest.raises(KeyError, match="already bound"):
+        env(DataclassConfig, name="STRUCTCONFIG")
+
+
+def test_reserved_names() -> None:
+    """Names used by fastapi-vue itself cannot be bound, by mangle or name=."""
+    with pytest.raises(KeyError, match="reserved"):
+        env(DataclassConfig, name="DEV")
+
+    @dataclasses.dataclass
+    class Dev:
+        x: int = 0
+
+    with pytest.raises(KeyError, match="reserved"):
+        env(Dev)
+
+
+def test_unsupported_type() -> None:
+    """Only dataclasses and msgspec.Structs can be bound."""
+    with pytest.raises(TypeError, match=r"dataclass or msgspec\.Struct"):
+        env(dict)
+
+
+def test_struct_teleport_and_decode() -> None:
+    """A mutated struct teleports; a fresh registry decodes it (worker view)."""
+    config = env(StructConfig)
+    config.port = 9000
+    teleport()
+    decoded = _Env()(StructConfig)
+    assert decoded == config
+    assert decoded is not config
+
+
+def test_dataclass_teleport_and_decode() -> None:
+    """Dataclasses round-trip through the environment via stdlib json."""
+    config = env(DataclassConfig)
+    config.host = "example.com"
+    teleport()
+    assert _Env()(DataclassConfig) == config
+
+
+def test_decode_on_bind_when_set(monkeypatch: pytest.MonkeyPatch) -> None:
+    """An already-set variable is decoded at binding time."""
+    monkeypatch.setenv("TEST_STRUCTCONFIG", '{"host": "example.com", "port": 1}')
+    assert env(StructConfig).host == "example.com"
+
+
+def test_teleport_without_prefix(monkeypatch: pytest.MonkeyPatch) -> None:
+    """teleport() with bindings but no FASTAPI_VUE prefix fails loudly."""
+    monkeypatch.delenv(PREFIX_VARIABLE)
+    env(StructConfig)
+    with pytest.raises(RuntimeError, match=PREFIX_VARIABLE):
+        teleport()
+
+
+def test_teleport_noop_without_bindings() -> None:
+    """No bindings: teleport() needs no prefix and does nothing."""
+    teleport()

fastapi-vue/tests/test_logging.py

@@ -0,0 +1,60 @@
+"""Tests for fastapi_vue.logging.patch_log_config overlay behavior."""
+
+import logging.config
+
+from fastapi_vue.logging import patch_log_config
+
+
+def test_empty_dict_overlays_uvicorn_defaults() -> None:
+    """An empty dict is a partial config: merged over uvicorn's defaults."""
+    config = patch_log_config({})
+    assert config["version"] == 1
+    assert config["disable_existing_loggers"] is False
+    assert config["root"]["handlers"] == ["default"]
+    assert "uvicorn" in config["loggers"]
+    logging.config.dictConfig(config)  # must be a valid, complete config
+
+
+def test_partial_logger_customization() -> None:
+    """The documented use case: only the customization, no boilerplate."""
+    config = patch_log_config({"loggers": {"kanta": {"level": "DEBUG"}}})
+    assert config["loggers"]["kanta"] == {"level": "DEBUG"}
+    assert config["loggers"]["uvicorn"]["handlers"] == ["default"]
+    assert config["loggers"]["watchfiles.main"]["level"] == "WARNING"
+    logging.config.dictConfig(config)
+    assert logging.getLogger("kanta").level == logging.DEBUG
+
+
+def test_overlay_root_level_wins() -> None:
+    """User-supplied root level is kept; our handler wiring still applies."""
+    config = patch_log_config({"root": {"level": "ERROR"}})
+    assert config["root"]["level"] == "ERROR"
+    assert config["root"]["handlers"] == ["default"]
+    logging.config.dictConfig(config)
+    assert logging.getLogger().level == logging.ERROR
+
+
+def test_overlay_formatter_customization_keeps_stock_siblings() -> None:
+    """A user formatter replaces ours; the access formatter still works."""
+    config = patch_log_config({"formatters": {"default": {"fmt": "%(name)s %(message)s"}}})
+    assert config["formatters"]["default"] == {
+        "()": "uvicorn.logging.DefaultFormatter",  # stock class, user's fmt
+        "fmt": "%(name)s %(message)s",
+        "use_colors": None,
+    }
+    assert "access" in config["formatters"]
+    logging.config.dictConfig(config)
+
+
+def test_full_config_used_as_is() -> None:
+    """A dict with version is complete: no uvicorn loggers appear."""
+    config = patch_log_config({"version": 1})
+    assert "uvicorn" not in config.get("loggers", {})
+    # No "default" handler exists, so root must not reference one.
+    assert "handlers" not in config["root"]
+    logging.config.dictConfig(config)
+
+
+def test_non_dict_passes_through() -> None:
+    """Non-dict configs (e.g. an ini file path) are returned untouched."""
+    assert patch_log_config("logging.ini") == "logging.ini"

fastapi_vue_setup.py

@@ -111,12 +111,14 @@ def ruff_format_content(
 
 
 def uv_add_packages(packages: list[str], *, cwd: Path, group: str | None = None) -> None:
-    """Add packages using uv."""
+    """Add packages using uv.
-    cmd = ["uv", "add", "-q", "-U"]
+
+    Uses --frozen so only pyproject.toml is edited, without locking or
+    syncing - those happen in a single uv sync step after all changes.
+    """
+    cmd = ["uv", "add", "-q", "--frozen"]
     if group:
         cmd.extend(["--group", group])
-    else:
-        cmd.append("--no-sync")
     cmd.extend(packages)
     result = subprocess.run(cmd, cwd=cwd, check=False)  # noqa: S603
     if result.returncode != 0:
@@ -161,7 +163,7 @@ NEW_BUILD_HOOK_PATH = "scripts/fastapi-vue/buildhook.py"
 # Frontend instantiation block for patching existing apps
 FRONTEND_BLOCK = """
 # Vue Frontend static files
-frontend = fastapi_vue.Frontend(Path(__file__).with_name("frontend-build"))
+frontend = Frontend(Path(__file__).with_name("frontend-build"))
 """
 
 # Lifespan block for patching apps that don't have one
@@ -473,6 +475,74 @@ def _find_app_in_subpackage(subpkg_dir: Path) -> tuple[Path, str] | None:
     return None
 
 
+def _migrate_devmode_in_main(content: str) -> str | None:
+    """Spot-patch the pre-1.6 DEVMODE mechanism to the FASTAPI_VUE env prefix.
+
+    Replaces `DEVMODE = os.getenv("PREFIX_DEV") == "1"` with
+    `os.environ["FASTAPI_VUE"] = "PREFIX"` and remaining DEVMODE references
+    with env.dev, ensuring env is imported from fastapi_vue.
+
+    Returns the patched content, or None if there was nothing to patch.
+    """
+    match = re.search(
+        r"^DEVMODE\s*=\s*os\.getenv\(\s*[\"']([A-Za-z0-9_]+)_DEV[\"']\s*\)\s*==\s*[\"']1[\"']",
+        content,
+        re.MULTILINE,
+    )
+    if not match:
+        return None
+    content = (
+        content[: match.start()]
+        + f'os.environ["FASTAPI_VUE"] = "{match.group(1)}"'
+        + content[match.end() :]
+    )
+    # Replace every remaining standalone DEVMODE reference (as in app.py
+    # migration, string literals are an accepted risk)
+    content = re.sub(r"(?<![\w.])DEVMODE\b", "env.dev", content)
+    if not re.search(r"^from fastapi_vue import\b.*\benv\b", content, re.MULTILINE):
+        if re.search(r"^from fastapi_vue import ", content, re.MULTILINE):
+            content = re.sub(
+                r"^from fastapi_vue import ",
+                "from fastapi_vue import env, ",
+                content,
+                count=1,
+                flags=re.MULTILINE,
+            )
+        else:
+            insert_line = find_import_insertion_line(content)
+            lines = content.splitlines(keepends=True)
+            insert_idx = insert_line - 1
+            import_text = "from fastapi_vue import env\n"
+            if insert_idx >= len(lines):
+                content = content.rstrip("\n") + "\n" + import_text
+            else:
+                content = "".join(lines[:insert_idx]) + import_text + "".join(lines[insert_idx:])
+    return content
+
+
+def _patch_main_devmode(path: Path, *, dry: bool) -> str | None:
+    """Apply _migrate_devmode_in_main to a main module in place, if needed.
+
+    Done in place even without the auto-upgrade marker: the marker guards
+    full-file overwrites, while leaving this change to a .new.py merge would
+    silently break dev mode for every customized pre-1.6 main.
+
+    Returns the migrated content if the module was (or would be) patched,
+    None if there was nothing to patch.
+    """
+    content = path.read_text("UTF-8")
+    migrated = _migrate_devmode_in_main(content)
+    if migrated is None:
+        return None
+    migrated = ruff_format_content(migrated, path, mode="isort")
+    if dry:
+        print(f"✅ Would patch {path} (DEVMODE → FASTAPI_VUE)")
+        return migrated
+    path.write_text(migrated, "UTF-8", newline="\n")
+    print(f"✅ Patched {path} (DEVMODE → FASTAPI_VUE)")
+    return migrated
+
+
 def _add_env_prefix_to_main(content: str) -> str:
     """Add FASTAPI_VUE environment prefix setup to an existing main module."""
     lines = content.splitlines()
@@ -600,10 +670,9 @@ def render_template(template: str, **kwargs: str) -> str:
 def needs_app_migration(project_dir: Path) -> bool:
     """Check if the project was set up with fastapi-vue older than 1.6.
 
-    Those versions patched app.py with `from fastapi_vue import Frontend` and
+    Those versions patched app.py with a DEVMODE import from the main module;
-    a DEVMODE import from the main module; 1.6+ uses fastapi_vue.Frontend and
+    1.6+ uses env.dev from fastapi_vue instead. Must be called before the
-    fastapi_vue.env. Must be called before the dependency step rewrites the
+    dependency step rewrites the fastapi-vue requirement in pyproject.toml.
-    fastapi-vue requirement in pyproject.toml.
     """
     pyproject = project_dir / "pyproject.toml"
     if not pyproject.exists():
@@ -624,8 +693,8 @@ def patch_app_file(
 
     Inserts imports at top (ruff will sort them), route at bottom,
     and tries to patch lifespan with frontend.load(). With migrate=True,
-    pre-1.6 patching (plain Frontend, DEVMODE import) is first rewritten
+    pre-1.6 patching (DEVMODE import from the main module) is first
-    to the current format.
+    rewritten to the current format (env.dev).
 
     Returns True if patched, False if already patched or failed.
     """
@@ -636,17 +705,18 @@ def patch_app_file(
     original_content = path.read_text("UTF-8")
     content = original_content
 
-    # Migrate pre-1.6 patching to the current format: Frontend via the
+    # Migrate pre-1.6 patching to the current format: DEVMODE via
-    # fastapi_vue module, DEVMODE via fastapi_vue.env
+    # fastapi_vue.env (the Frontend import stays as-is)
     if migrate:
-        if "from fastapi_vue import Frontend\n" in content:
-            content = content.replace("from fastapi_vue import Frontend\n", "")
-            content = re.sub(r"(?<![\w.])Frontend\(", "fastapi_vue.Frontend(", content)
         old_import = f"from {main_module_path} import DEVMODE"
         if old_import in content:
-            has_plain_import = re.search(r"^import fastapi_vue$", content, re.MULTILINE)
+            # The import sort at the end merges this with any existing
-            content = content.replace(old_import, "" if has_plain_import else "import fastapi_vue")
+            # `from fastapi_vue import Frontend` line
-            content = content.replace("debug=DEVMODE", "debug=fastapi_vue.env.dev")
+            content = content.replace(old_import, "from fastapi_vue import env")
+            # Replace every remaining standalone DEVMODE reference (not just
+            # the debug= parameter); it may also appear inside string literals,
+            # but that's an accepted risk over AST rewriting
+            content = re.sub(r"(?<![\w.])DEVMODE\b", "env.dev", content)
 
     # Check what's already patched; plain "Frontend(" so user modifications
     # of the integration (renames, different call shape) still count
@@ -662,12 +732,14 @@ def patch_app_file(
     route_line = f'frontend.route({app_var}, "/")'
 
     # Add missing imports (using AST to find correct insertion point);
-    # every patch path uses fastapi_vue.*, so always ensure the plain import
+    # the import sort at the end merges duplicate from-imports
     imports = []
     if not has_frontend:
         imports.append("from pathlib import Path")
-    if not re.search(r"^import fastapi_vue$", content, re.MULTILINE):
+    if not has_frontend or not re.search(
-        imports.append("import fastapi_vue")
+        r"^from fastapi_vue import\b.*\benv\b", content, re.MULTILINE
+    ):
+        imports.append("from fastapi_vue import Frontend, env")
     if imports:
         insert_line = find_import_insertion_line(content)
         lines = content.splitlines(keepends=True)
@@ -702,14 +774,14 @@ def patch_app_file(
         lines.append(route_line)
         content = "\n".join(lines)
 
-    # Try to patch FastAPI() call with debug=fastapi_vue.env.dev if no debug arg exists
+    # Try to patch FastAPI() call with debug=env.dev if no debug arg exists
     if not has_debug_arg:
         fastapi_pattern = r"(\w+\s*=\s*FastAPI\s*\()([^)]*)\)"
         for match in re.finditer(fastapi_pattern, content, re.DOTALL):
             args = match.group(2)
             if "debug" not in args:
-                # Add debug=fastapi_vue.env.dev as last argument
+                # Add debug=env.dev as last argument
-                new_args = (f"{args}, " if args.strip() else "") + "debug=fastapi_vue.env.dev"
+                new_args = (f"{args}, " if args.strip() else "") + "debug=env.dev"
                 content = (
                     content[: match.start()]
                     + match.group(1)
@@ -1008,6 +1080,11 @@ def _upgrade_old_vite_plugin(path: Path, module_name: str, *, dry: bool = False)
 _new_files_written: list[tuple[Path, Path]] = []
 
 
+def _strip_upgrade_marker(content: str) -> str:
+    """Remove the auto-upgrade marker line, for content comparison."""
+    return "\n".join(line for line in content.splitlines() if UPGRADE_MARKER not in line)
+
+
 def write_file(
     path: Path,
     content: str,
@@ -1531,7 +1608,19 @@ def cmd_setup(args: argparse.Namespace) -> int:
     main_content = render_template(template, **tpl_vars)
 
     if main_file.exists():
-        # File exists: update if it has the auto-upgrade marker, otherwise use fallback
+        # Spot-patch the pre-1.6 DEVMODE mechanism in place first - the
+        # auto-upgrade marker guards full-file overwrites, but leaving this
+        # change to a .new.py merge would silently break dev mode
+        migrated = _patch_main_devmode(main_file, dry=dry)
+        existing = migrated if migrated is not None else main_file.read_text("UTF-8")
+        # Update if it has the auto-upgrade marker, otherwise use fallback -
+        # unless the markerless file is otherwise up to date (e.g. the
+        # DEVMODE spot-patch was the only change), then no fallback is needed
+        if UPGRADE_MARKER not in existing and _strip_upgrade_marker(
+            existing
+        ) == _strip_upgrade_marker(ruff_format_content(main_content, main_file)):
+            print(f"✔️  {main_file} (already up to date)")
+        else:
             write_file(
                 main_file,
                 main_content,
@@ -1558,7 +1647,8 @@ def cmd_setup(args: argparse.Namespace) -> int:
             executable=False,
         )
         if main.exists():
-            content = main.read_text("UTF-8")
+            migrated = _patch_main_devmode(main, dry=dry)
+            content = migrated if migrated is not None else main.read_text("UTF-8")
             if "FASTAPI_VUE" not in content:
                 new_content = _add_env_prefix_to_main(content)
                 new_file = main.with_suffix(".new.py")
@@ -1651,9 +1741,16 @@ def cmd_setup(args: argparse.Namespace) -> int:
     fastapi_vue_req = f"fastapi-vue~={mmp[1]}.{mmp[2]}.{mmp[3]}" if mmp else "fastapi-vue"
     if dry:
         print(f"📦 Would add: fastapi[standard], {fastapi_vue_req}")
+        print("📦 Would run: uv sync")
     else:
         print("📦 Dependencies")
         uv_add_packages(["fastapi[standard]", fastapi_vue_req], cwd=project_dir)
+        # uv add runs with --frozen, so lock and sync the environment once
+        # everything is in place; attached to the terminal so the user sees
+        # the updates, and non-fatal - setup is complete either way
+        result = subprocess.run(["uv", "sync"], cwd=project_dir, check=False)  # noqa: S607
+        if result.returncode != 0:
+            print("⚠️  uv sync failed - run it manually to update the environment")
 
     print()
     print_boxed("Setup complete!")

pyproject.toml

@@ -49,3 +49,4 @@ ignore = ["CPY", "D203", "D213", "COM812", "PLR2004"]
 "template/**" = ["F821"]  # Undefined names are template placeholders
 "template/scripts/devserver.py" = ["N806"]  # MODULE_NAME is a template variable
 "fastapi_vue_setup.py" = ["PLR", "C901", "T201", "RUF001"]
+"**/tests/**" = ["S101"]  # Asserts are the point of tests

template/backend/__main__.py

@@ -5,8 +5,7 @@ import argparse
 import os
 from pathlib import Path
 
-import fastapi_vue
+from fastapi_vue import env, server
-from fastapi_vue import server
 
 DEFAULT_PORT = TEMPLATE_DEFAULT_PORT
 os.environ["FASTAPI_VUE"] = "ENVPREFIX"
@@ -27,7 +26,7 @@ def main() -> None:
         listen=args.listen,
         default_port=DEFAULT_PORT,
         server_header=False,
-        reload=Path(__file__).parent if fastapi_vue.env.dev else False,
+        reload=Path(__file__).parent if env.dev else False,
     )
 
 

template/backend/app.py

@@ -4,11 +4,11 @@ from collections.abc import AsyncGenerator
 from contextlib import asynccontextmanager
 from pathlib import Path
 
-import fastapi_vue
 from fastapi import FastAPI
+from fastapi_vue import Frontend, env
 
 # Vue Frontend static files
-frontend = fastapi_vue.Frontend(Path(__file__).with_name("frontend-build"))
+frontend = Frontend(Path(__file__).with_name("frontend-build"))
 
 
 @asynccontextmanager
@@ -18,7 +18,7 @@ async def lifespan(_app: FastAPI) -> AsyncGenerator:
     yield
 
 
-app = FastAPI(title="PROJECT_TITLE", debug=fastapi_vue.env.dev, lifespan=lifespan)
+app = FastAPI(title="PROJECT_TITLE", debug=env.dev, lifespan=lifespan)
 
 
 # Add API routes here...