Ensure extra='forbid' is enforced in DotEnvSettingsSource when env_prefix is specified

pydantic_settings/sources.py

@@ -640,12 +640,17 @@ def __call__(self) -> dict[str, Any]:
         data: dict[str, Any] = super().__call__()
 
         data_lower_keys: list[str] = []
+        is_extra_allowed = self.config.get('extra') != 'forbid'
         if not self.case_sensitive:
             data_lower_keys = [x.lower() for x in data.keys()]
-
         # As `extra` config is allowed in dotenv settings source, We have to
         # update data with extra env variabels from dotenv file.
         for env_name, env_value in self.env_vars.items():
+            if not is_extra_allowed and not env_name.startswith(self.env_prefix):
+                raise SettingsError(
+                    "unable to load environment variables from dotenv file "
+                    f"due to the presence of variables without the specified prefix - '{self.env_prefix}'"
+                )
             if env_name.startswith(self.env_prefix) and env_value is not None:
                 env_name_without_prefix = env_name[self.env_prefix_len :]
                 first_key, *_ = env_name_without_prefix.split(self.env_nested_delimiter)

tests/test_settings.py

@@ -767,7 +767,6 @@ class Settings(BaseSettings):
 
 prefix_b='better string'
 prefix_c="best string"
-f="random value"
 """
 
 
@@ -790,6 +789,54 @@ class Settings(BaseSettings):
     assert s.c == 'best string'
 
 
+prefix_test_env_invalid_file = """\
+# this is a comment
+prefix_A=good string
+# another one, followed by whitespace
+
+prefix_b='better string'
+prefix_c="best string"
+f="random value"
+"""
+
+
+def test_env_file_with_env_prefix_invalid(tmp_path):
+    p = tmp_path / '.env'
+    p.write_text(prefix_test_env_invalid_file)
+
+    class Settings(BaseSettings):
+        a: str
+        b: str
+        c: str
+
+        model_config = SettingsConfigDict(env_file=p, env_prefix='prefix_')
+
+    err_msg = (
+        "unable to load environment variables from dotenv file "
+        "due to the presence of variables without the specified prefix - 'prefix_'"
+    )
+    with pytest.raises(SettingsError, match=err_msg):
+        Settings()
+
+
+def test_ignore_env_file_with_env_prefix_invalid(tmp_path):
+    p = tmp_path / '.env'
+    p.write_text(prefix_test_env_invalid_file)
+
+    class Settings(BaseSettings):
+        a: str
+        b: str
+        c: str
+
+        model_config = SettingsConfigDict(env_file=p, env_prefix='prefix_', extra='ignore')
+
+    s = Settings()
+
+    assert s.a == 'good string'
+    assert s.b == 'better string'
+    assert s.c == 'best string'
+
+
 def test_env_file_config_case_sensitive(tmp_path):
     p = tmp_path / '.env'
     p.write_text(test_env_file)