Add deprecation policy

docs/deprecation.md

@@ -0,0 +1,66 @@
+# Deprecation Policy
+
+The goal of this policy is to reduce the impact of changes on users and developers of the project by providing
+clear guidelines and a well-defined process for deprecating functionalities. This policy applies to both features
+and API interfaces.
+
+This policy describes what Starlette should follow pre-1.0, and what Starlette will follow post-1.0.
+
+## Starlette Versions
+
+Starlette follows [Semantic Versioning](https://semver.org/), with some additional constraints.
+While we are pre-1.0, we treat any SemVer changes requiring a:
+
+- **major** bump as a change requiring a **minor** bump.
+- **minor** bump as a change requiring a **patch** bump.
+
+## Deprecation Types
+
+We'll consider two kinds of deprecations: **Python version** and **feature** deprecations.
+
+### Python Version Deprecation
+
+Starlette will aim to support a Python version until the [EOL date of that version](https://endoflife.date/python).
+When a Python version reaches EOL, Starlette will drop support for that version in the next minor release.
+
+!!! warning
+    Pre-1.0 Starlette will also drop support in the next minor release.
+
+The drop of Python version support will be documented in the release notes, but the user will **not** be warned it.
+
+### Feature Deprecation
+
+Starlette will deprecate a feature in the next minor release after the feature is marked as deprecated.
+
+The deprecation of a feature needs to be followed by a warning message using `warnings.warn` in the code that
+uses the deprecated feature. The warning message should include the version in which the feature will be removed.
+
+The format of the message should follow:
+
+> *`code` is deprecated and will be removed in version `version`.*
+
+The `code` can be a *function*, *module* or *feature* name, and the `version` should be the next major release.
+
+The deprecation warning may include an advice on how to replace the deprecated feature.
+
+> *Use `alternative` instead.*
+
+As a full example, imagine we are in version 1.0.0, and we want to deprecate the `potato` function.
+We would add the follow warning:
+
+```python
+def potato():
+    warnings.warn(
+        "potato is deprecated and will be removed in version 2.0.0. "
+        "Use banana instead.",
+        DeprecationWarning,
+    )
+
+def banana():
+    ...
+```
+
+!!! warning
+    Pre-1.0 Starlette will remove deprecated code in the stable release (1.0).
+
+The drop of a feature will be documented in the release notes, and the user will be warned about it.

mkdocs.yml

@@ -45,6 +45,7 @@ nav:
   - Test Client: 'testclient.md'
   - Third Party Packages: 'third-party-packages.md'
   - Contributing: 'contributing.md'
+  - Deprecation Policy: 'deprecation.md'
   - Release Notes: 'release-notes.md'
 
 markdown_extensions:
@@ -53,7 +54,7 @@ markdown_extensions:
   - pymdownx.highlight
   - pymdownx.superfences
   - pymdownx.tabbed:
-      alternate_style: true 
+      alternate_style: true
 
 extra_javascript:
   - 'js/chat.js'

setup.cfg

@@ -28,12 +28,12 @@ xfail_strict=True
 filterwarnings=
     # Turn warnings that aren't filtered into exceptions
     error
-    ignore: run_until_first_complete is deprecated and will be removed in a future version.:DeprecationWarning
-    ignore: starlette\.middleware\.wsgi is deprecated and will be removed in a future release\.*:DeprecationWarning
+    ignore: run_until_first_complete is deprecated, and will be removed in version 1\.0\.0\.:DeprecationWarning
+    ignore: starlette\.middleware\.wsgi is deprecated, and will be removed in version 1\.0\.0.*:DeprecationWarning
     ignore: Async generator 'starlette\.requests\.Request\.stream' was garbage collected before it had been exhausted.*:ResourceWarning
     ignore: path is deprecated.*:DeprecationWarning:certifi
     ignore: Use 'content=<...>' to upload raw bytes/text content.:DeprecationWarning
-    ignore: The `allow_redirects` argument is deprecated. Use `follow_redirects` instead.:DeprecationWarning
+    ignore: `allow_redirects` argument is deprecated, and will be removed in version 1\.0\.0\. Use `follow_redirects` instead.:DeprecationWarning
     ignore: 'cgi' is deprecated and slated for removal in Python 3\.13:DeprecationWarning
 
 [coverage:run]

starlette/concurrency.py

@@ -17,8 +17,7 @@
 
 async def run_until_first_complete(*args: typing.Tuple[typing.Callable, dict]) -> None:
     warnings.warn(
-        "run_until_first_complete is deprecated "
-        "and will be removed in a future version.",
+        "run_until_first_complete is deprecated, and will be removed in version 1.0.0.",
         DeprecationWarning,
     )
 

starlette/exceptions.py

@@ -41,7 +41,8 @@ def __getattr__(name: str) -> typing.Any:  # pragma: no cover
         from starlette.middleware.exceptions import ExceptionMiddleware
 
         warnings.warn(
-            f"{__deprecated__} is deprecated on `starlette.exceptions`. "
+            f"{__deprecated__} is deprecated on `starlette.exceptions`, "
+            "and will be removed in version 1.0.0. "
             f"Import it from `starlette.middleware.exceptions` instead.",
             category=DeprecationWarning,
             stacklevel=3,

starlette/middleware/wsgi.py

@@ -9,7 +9,7 @@
 from starlette.types import Receive, Scope, Send
 
 warnings.warn(
-    "starlette.middleware.wsgi is deprecated and will be removed in a future release. "
+    "starlette.middleware.wsgi is deprecated, and will be removed in version 1.0.0. "
     "Please refer to https://github.com/abersheeran/a2wsgi as a replacement.",
     DeprecationWarning,
 )

starlette/routing.py

@@ -45,7 +45,7 @@ def iscoroutinefunction_or_partial(obj: typing.Any) -> bool:  # pragma: no cover
     """
     warnings.warn(
         "iscoroutinefunction_or_partial is deprecated, "
-        "and will be removed in a future release.",
+        "and will be removed in version 1.0.0.",
         DeprecationWarning,
     )
     while isinstance(obj, functools.partial):
@@ -597,17 +597,19 @@ def __init__(
 
         elif inspect.isasyncgenfunction(lifespan):
             warnings.warn(
-                "async generator function lifespans are deprecated, "
-                "use an @contextlib.asynccontextmanager function instead",
+                "Usage of async generator function lifespans is deprecated, "
+                "and will be removed in version 1.0.0. "
+                "Use an @contextlib.asynccontextmanager function instead.",
                 DeprecationWarning,
             )
             self.lifespan_context = asynccontextmanager(
                 lifespan,  # type: ignore[arg-type]
             )
         elif inspect.isgeneratorfunction(lifespan):
             warnings.warn(
-                "generator function lifespans are deprecated, "
-                "use an @contextlib.asynccontextmanager function instead",
+                "Usage of generator function lifespans is deprecated, "
+                "and will be removed in version 1.0.0. "
+                "Use an @contextlib.asynccontextmanager function instead.",
                 DeprecationWarning,
             )
             self.lifespan_context = _wrap_gen_lifespan_context(

starlette/status.py

@@ -187,7 +187,8 @@ def __getattr__(name: str) -> int:
     deprecated = __deprecated__.get(name)
     if deprecated:
         warnings.warn(
-            f"'{name}' is deprecated. Use '{deprecation_changes[name]}' instead.",
+            f"'{name}' is deprecated, and will be removed in version 1.0.0. "
+            f"Use '{deprecation_changes[name]}' instead.",
             category=DeprecationWarning,
             stacklevel=3,
         )

starlette/testclient.py

@@ -407,11 +407,12 @@ def _choose_redirect_arg(
             bool, httpx._client.UseClientDefault
         ] = httpx._client.USE_CLIENT_DEFAULT
         if allow_redirects is not None:
-            message = (
-                "The `allow_redirects` argument is deprecated. "
-                "Use `follow_redirects` instead."
+            warnings.warn(
+                "`allow_redirects` argument is deprecated, "
+                "and will be removed in version 1.0.0. "
+                "Use `follow_redirects` instead.",
+                DeprecationWarning,
             )
-            warnings.warn(message, DeprecationWarning)
             redirect = allow_redirects
         if follow_redirects is not None:
             redirect = follow_redirects

tests/test_applications.py

@@ -380,8 +380,9 @@ async def lifespan(app):
 
 deprecated_lifespan = pytest.mark.filterwarnings(
     r"ignore"
-    r":(async )?generator function lifespans are deprecated, use an "
-    r"@contextlib\.asynccontextmanager function instead"
+    r":Usage of (async )?generator function lifespans is deprecated, "
+    r"and will be removed in version 1.0.0. "
+    r"Use an @contextlib\.asynccontextmanager function instead."
     r":DeprecationWarning"
     r":starlette.routing"
 )

tests/test_status.py

@@ -8,12 +8,14 @@
     (
         (
             "WS_1004_NO_STATUS_RCVD",
-            "'WS_1004_NO_STATUS_RCVD' is deprecated. "
+            "'WS_1004_NO_STATUS_RCVD' is deprecated, "
+            "and will be removed in version 1.0.0. "
             "Use 'WS_1005_NO_STATUS_RCVD' instead.",
         ),
         (
             "WS_1005_ABNORMAL_CLOSURE",
-            "'WS_1005_ABNORMAL_CLOSURE' is deprecated. "
+            "'WS_1005_ABNORMAL_CLOSURE' is deprecated, "
+            "and will be removed in version 1.0.0. "
             "Use 'WS_1006_ABNORMAL_CLOSURE' instead.",
         ),
     ),