use FutureWarning in settings so it's printed (#881)

* use FutureWarning in settings so it's printed

* fix tests

* better warning link

* change warning link

changes/881-samuelcolvin.md

@@ -0,0 +1 @@
+Use `FutureWarning` instead of `DeprecationWarning` when `alias` instead of `env` is used for settings models

pydantic/env_settings.py

@@ -73,8 +73,9 @@ class BaseSettings(BaseModel):
                 if field.has_alias:
                     warnings.warn(
                         'aliases are no longer used by BaseSettings to define which environment variables to read. '
-                        'Instead use the "env" field setting. See https://pydantic-docs.helpmanual.io/usage/settings/',
-                        DeprecationWarning,
+                        'Instead use the "env" field setting. '
+                        'See https://pydantic-docs.helpmanual.io/usage/settings/#environment-variable-names',
+                        FutureWarning,
                     )
                 env_names = [cls.env_prefix + field.name]
             elif isinstance(env, str):

tests/test_settings.py

@@ -208,7 +208,7 @@ def test_env_field(env):
 
 
 def test_aliases_warning(env):
-    with pytest.warns(DeprecationWarning, match='aliases are no longer used by BaseSettings'):
+    with pytest.warns(FutureWarning, match='aliases are no longer used by BaseSettings'):
 
         class Settings(BaseSettings):
             foobar: str = 'default value'