Restore old documented functionality, add optional warning, document the warning

docs/config.md

@@ -11,7 +11,8 @@ from starlette.config import Config
 from starlette.datastructures import CommaSeparatedStrings, Secret
 
 # Config will be read from environment variables and/or ".env" files.
-config = Config(".env")
+# If warn_missing is set then warning is given if .env -file is not found.
+config = Config(".env", warn_missing=True)
 
 DEBUG = config('DEBUG', cast=bool, default=False)
 DATABASE_URL = config('DATABASE_URL')

starlette/config.py

@@ -2,6 +2,7 @@
 
 import os
 import typing
+import warnings
 from pathlib import Path
 
 
@@ -56,13 +57,17 @@ def __init__(
         env_file: str | Path | None = None,
         environ: typing.Mapping[str, str] = environ,
         env_prefix: str = "",
+        *,
+        warn_missing: bool = False,
     ) -> None:
         self.environ = environ
         self.env_prefix = env_prefix
         self.file_values: typing.Dict[str, str] = {}
         if env_file is not None:
             if not os.path.isfile(env_file):
-                raise FileNotFoundError(f"Config file '{env_file}' not found.")
+                if warn_missing:
+                    warnings.warn(f"{env_file} not found")
+                return
             self.file_values = self._read_file(env_file)
 
     @typing.overload

tests/test_config.py

@@ -1,5 +1,6 @@
 import os
 import typing
+import warnings
 from pathlib import Path
 from typing import Any, Optional
 
@@ -105,11 +106,15 @@ def cast_to_int(v: typing.Any) -> int:
         config.get("BOOL_AS_INT", cast=bool)
 
 
-def test_missing_env_file_raises(tmpdir: Path) -> None:
+def test_missing_env_file_warns_only_if_requested(tmpdir: Path) -> None:
     path = os.path.join(tmpdir, ".env")
 
-    with pytest.raises(FileNotFoundError, match=f"Config file '{path}' not found."):
+    with warnings.catch_warnings(record=True) as caught:
         Config(path)
+        assert not caught
+        with pytest.raises(UserWarning):
+            Config(path, warn_missing=True)
+            assert caught
 
 
 def test_environ() -> None: