respect env_prefix when extra allowed (#238)

pydantic_settings/sources.py

@@ -683,9 +683,10 @@ def _read_env_files(self) -> Mapping[str, str | None]:
 
     def __call__(self) -> dict[str, Any]:
         data: dict[str, Any] = super().__call__()
+        is_extra_allowed = self.config.get('extra') != 'forbid'
 
         # As `extra` config is allowed in dotenv settings source, We have to
-        # update data with extra env variabels from dotenv file.
+        # update data with extra env variables from dotenv file.
         for env_name, env_value in self.env_vars.items():
             if not env_value:
                 continue
@@ -696,7 +697,12 @@ def __call__(self) -> dict[str, Any]:
                         env_used = True
                         break
             if not env_used:
-                data[env_name] = env_value
+                if is_extra_allowed and env_name.startswith(self.env_prefix):
+                    # env_prefix should be respected and removed from the env_name
+                    normalized_env_name = env_name[len(self.env_prefix) :]
+                    data[normalized_env_name] = env_value
+                else:
+                    data[env_name] = env_value
         return data
 
     def __repr__(self) -> str:

tests/test_settings.py

@@ -2354,3 +2354,16 @@ class Settings(BaseSettings):
 
     s = Settings()
     assert s.model_dump() == {'foo': '', 'bar_alias': '0', 'nested_alias': {'a': '1', 'b': '2'}}
+
+
+def test_dotenv_with_extra_and_env_prefix(tmp_path):
+    p = tmp_path / '.env'
+    p.write_text('xxx__foo=1\nxxx__extra_var=extra_value')
+
+    class Settings(BaseSettings):
+        model_config = SettingsConfigDict(extra='allow', env_file=p, env_prefix='xxx__')
+
+        foo: str = ''
+
+    s = Settings()
+    assert s.model_dump() == {'foo': '1', 'extra_var': 'extra_value'}