Add the "base" config level concept, to allow configuration of all virtual environments sharing the same base.

The new functionality serves a use case which was not previously possible with pip configuration files, namely the situation where you have a base Python installation and want to influence the pip configuration for all derivative virtual environments *without* changing the config for all other environments on a machine (global), or for all other environment run by the same user (user). Concretely, this could be used for a centrally managed network mounted filesystem based Python installation, from which multiple users can build virtual environments and inside which a specific pip configuration is needed (e.g. an index URL).

Author: pelson

docs/html/topics/configuration.md

@@ -19,13 +19,14 @@ and how they are related to pip's various command line options.
 
 ## Configuration Files
 
-Configuration files can change the default values for command line option.
-They are written using a standard INI style configuration files.
+Configuration files can change the default values for command line options.
+They are written using standard INI style configuration files.
 
-pip has 3 "levels" of configuration files:
+pip has 4 "levels" of configuration files:
 
-- `global`: system-wide configuration file, shared across users.
-- `user`: per-user configuration file.
+- `global`: system-wide configuration file, shared across all users.
+- `user`: per-user configuration file, shared across all environments.
+- `base` : per-base environment configuration file, shared across all virtualenvs with the same base. (added in pip `v23`)
 - `site`: per-environment configuration file; i.e. per-virtualenv.
 
 ### Location
@@ -47,8 +48,11 @@ User
 
   The legacy "per-user" configuration file is also loaded, if it exists: {file}`$HOME/.pip/pip.conf`.
 
+Base
+: {file}`\{sys.base_prefix\}/pip.conf`
+
 Site
-: {file}`$VIRTUAL_ENV/pip.conf`
+: {file}`\{sys.prefix\}/pip.conf`
 ```
 
 ```{tab} MacOS
@@ -63,8 +67,11 @@ User
 
   The legacy "per-user" configuration file is also loaded, if it exists: {file}`$HOME/.pip/pip.conf`.
 
+Base
+: {file}`\{sys.base_prefix\}/pip.conf`
+
 Site
-: {file}`$VIRTUAL_ENV/pip.conf`
+: {file}`\{sys.prefix\}/pip.conf`
 ```
 
 ```{tab} Windows
@@ -81,8 +88,11 @@ User
 
   The legacy "per-user" configuration file is also loaded, if it exists: {file}`%HOME%\\pip\\pip.ini`
 
+Base
+: {file}`\{sys.base_prefix\}\\pip.ini`
+
 Site
-: {file}`%VIRTUAL_ENV%\\pip.ini`
+: {file}`\{sys.prefix\}\\pip.ini`
 ```
 
 ### `PIP_CONFIG_FILE`
@@ -102,6 +112,7 @@ order:
 - `PIP_CONFIG_FILE`, if given.
 - Global
 - User
+- Base
 - Site
 
 Each file read overrides any values read from previous files, so if the

news/9752.feature.rst

@@ -0,0 +1 @@
+In the case of virtual environments, configuration files are now also included from the base installation.

src/pip/_internal/configuration.py

@@ -36,12 +36,20 @@
 kinds = enum(
     USER="user",  # User Specific
     GLOBAL="global",  # System Wide
-    SITE="site",  # [Virtual] Environment Specific
+    BASE="base",  # Base environment specific (e.g. for all venvs with the same base)
+    SITE="site",  # Environment Specific (e.g. per venv)
     ENV="env",  # from PIP_CONFIG_FILE
     ENV_VAR="env-var",  # from Environment Variables
 )
-OVERRIDE_ORDER = kinds.GLOBAL, kinds.USER, kinds.SITE, kinds.ENV, kinds.ENV_VAR
-VALID_LOAD_ONLY = kinds.USER, kinds.GLOBAL, kinds.SITE
+OVERRIDE_ORDER = (
+    kinds.GLOBAL,
+    kinds.USER,
+    kinds.BASE,
+    kinds.SITE,
+    kinds.ENV,
+    kinds.ENV_VAR,
+)
+VALID_LOAD_ONLY = kinds.USER, kinds.GLOBAL, kinds.BASE, kinds.SITE
 
 logger = getLogger(__name__)
 
@@ -70,6 +78,7 @@ def get_configuration_files() -> Dict[Kind, List[str]]:
         os.path.join(path, CONFIG_BASENAME) for path in appdirs.site_config_dirs("pip")
     ]
 
+    base_config_file = os.path.join(sys.base_prefix, CONFIG_BASENAME)
     site_config_file = os.path.join(sys.prefix, CONFIG_BASENAME)
     legacy_config_file = os.path.join(
         os.path.expanduser("~"),
@@ -78,6 +87,7 @@ def get_configuration_files() -> Dict[Kind, List[str]]:
     )
     new_config_file = os.path.join(appdirs.user_config_dir("pip"), CONFIG_BASENAME)
     return {
+        kinds.BASE: [base_config_file],
         kinds.GLOBAL: global_config_files,
         kinds.SITE: [site_config_file],
         kinds.USER: [legacy_config_file, new_config_file],
@@ -344,6 +354,8 @@ def iter_config_files(self) -> Iterable[Tuple[Kind, List[str]]]:
             # The legacy config file is overridden by the new config file
             yield kinds.USER, config_files[kinds.USER]
 
+        yield kinds.BASE, config_files[kinds.BASE]
+
         # finally virtualenv configuration first trumping others
         yield kinds.SITE, config_files[kinds.SITE]
 

tests/unit/test_configuration.py

@@ -24,12 +24,18 @@ def test_user_loading(self) -> None:
         self.configuration.load()
         assert self.configuration.get_value("test.hello") == "2"
 
-    def test_site_loading(self) -> None:
-        self.patch_configuration(kinds.SITE, {"test.hello": "3"})
+    def test_base_loading(self) -> None:
+        self.patch_configuration(kinds.BASE, {"test.hello": "3"})
 
         self.configuration.load()
         assert self.configuration.get_value("test.hello") == "3"
 
+    def test_site_loading(self) -> None:
+        self.patch_configuration(kinds.SITE, {"test.hello": "4"})
+
+        self.configuration.load()
+        assert self.configuration.get_value("test.hello") == "4"
+
     def test_environment_config_loading(self, monkeypatch: pytest.MonkeyPatch) -> None:
         contents = """
             [test]
@@ -107,6 +113,15 @@ def test_no_such_key_error_message_missing_option(self) -> None:
         with pytest.raises(ConfigurationError, match=pat):
             self.configuration.get_value("global.index-url")
 
+    def test_overrides_normalization(self) -> None:
+        # Check that normalized names are used in precedence calculations.
+        # Reminder: USER has higher precedence than GLOBAL.
+        self.patch_configuration(kinds.USER, {"test.hello-world": "1"})
+        self.patch_configuration(kinds.GLOBAL, {"test.hello_world": "0"})
+        self.configuration.load()
+
+        assert self.configuration.get_value("test.hello_world") == "1"
+
 
 class TestConfigurationPrecedence(ConfigurationMixin):
     # Tests for methods to that determine the order of precedence of
@@ -133,6 +148,13 @@ def test_env_overides_global(self) -> None:
 
         assert self.configuration.get_value("test.hello") == "0"
 
+    def test_site_overides_base(self) -> None:
+        self.patch_configuration(kinds.BASE, {"test.hello": "2"})
+        self.patch_configuration(kinds.SITE, {"test.hello": "1"})
+        self.configuration.load()
+
+        assert self.configuration.get_value("test.hello") == "1"
+
     def test_site_overides_user(self) -> None:
         self.patch_configuration(kinds.USER, {"test.hello": "2"})
         self.patch_configuration(kinds.SITE, {"test.hello": "1"})
@@ -147,6 +169,13 @@ def test_site_overides_global(self) -> None:
 
         assert self.configuration.get_value("test.hello") == "1"
 
+    def test_base_overides_user(self) -> None:
+        self.patch_configuration(kinds.USER, {"test.hello": "2"})
+        self.patch_configuration(kinds.BASE, {"test.hello": "1"})
+        self.configuration.load()
+
+        assert self.configuration.get_value("test.hello") == "1"
+
     def test_user_overides_global(self) -> None:
         self.patch_configuration(kinds.GLOBAL, {"test.hello": "3"})
         self.patch_configuration(kinds.USER, {"test.hello": "2"})

tests/unit/test_options.py

@@ -588,7 +588,7 @@ def test_venv_config_file_found(self, monkeypatch: pytest.MonkeyPatch) -> None:
         for _, val in cp.iter_config_files():
             files.extend(val)
 
-        assert len(files) == 4
+        assert len(files) == 5
 
     @pytest.mark.parametrize(
         "args, expect",