Revert "Add variable expansion (fix #421)"

This reverts commit c61bfb0.

CHANGELOG.rst

@@ -7,7 +7,10 @@ and this project adheres to `Semantic Versioning <https://semver.org/spec/v2.0.0
 
 `v0.12.0`_ - 00-Unreleased-2023
 -------------------------------
-
+Fixed
++++++
+- Revert "Add variable expansion." feature
+  due to `#490 <https://github.com/joke2k/django-environ/issues/490>`_.
 
 
 `v0.11.1`_ - 30-August-2023
@@ -402,4 +405,4 @@ Added
 .. _v0.4.1: https://github.com/joke2k/django-environ/compare/v0.4...v0.4.1
 .. _v0.4: https://github.com/joke2k/django-environ/compare/v0.3.1...v0.4
 .. _v0.3.1: https://github.com/joke2k/django-environ/compare/v0.3...v0.3.1
-.. _v0.3: https://github.com/joke2k/django-environ/compare/v0.2.1...v0.3
+.. _v0.3: https://github.com/joke2k/django-environ/compare/v0.2.1...v0.3

docs/quickstart.rst

@@ -23,28 +23,6 @@ And use it with ``settings.py`` as follows:
    :start-after: -code-begin-
    :end-before: -overview-
 
-Variables can contain references to another variables: ``$VAR`` or ``${VAR}``.
-Referenced variables are searched in the environment and within all definitions
-in the ``.env`` file. References are checked for recursion (self-reference).
-Exception is thrown if any reference results in infinite loop on any level
-of recursion. Variable values are substituted similar to shell parameter
-expansion. Example:
-
-.. code-block:: shell
-
-   # shell
-   export POSTGRES_USERNAME='user' POSTGRES_PASSWORD='SECRET'
-
-.. code-block:: shell
-
-   # .env
-   POSTGRES_HOSTNAME='example.com'
-   POSTGRES_DB='database'
-   DATABASE_URL="postgres://${POSTGRES_USERNAME}:${POSTGRES_PASSWORD}@${POSTGRES_HOSTNAME}:5432/${POSTGRES_DB}"
-
-The value of ``DATABASE_URL`` variable will become
-``postgres://user:SECRET@example.com:5432/database``.
-
 The ``.env`` file should be specific to the environment and not checked into
 version control, it is best practice documenting the ``.env`` file with an example.
 For example, you can also add ``.env.dist`` with a template of your variables to

environ/environ.py

@@ -17,9 +17,7 @@
 import os
 import re
 import sys
-import threading
 import warnings
-from os.path import expandvars
 from urllib.parse import (
     parse_qs,
     ParseResult,
@@ -42,9 +40,6 @@
 Openable = (str, os.PathLike)
 logger = logging.getLogger(__name__)
 
-# Variables which values should not be expanded
-NOT_EXPANDED = 'DJANGO_SECRET_KEY', 'CACHE_URL'
-
 
 def _cast(value):
     # Safely evaluate an expression node or a string containing a Python
@@ -194,11 +189,7 @@ class Env:
                             for s in ('', 's')]
     CLOUDSQL = 'cloudsql'
 
-    VAR = re.compile(r'(?<!\\)\$\{?(?P<name>[A-Z_][0-9A-Z_]*)}?',
-                     re.IGNORECASE)
-
     def __init__(self, **scheme):
-        self._local = threading.local()
         self.smart_cast = True
         self.escape_proxy = False
         self.prefix = ""
@@ -352,13 +343,9 @@ def path(self, var, default=NOTSET, **kwargs):
         """
         return Path(self.get_value(var, default=default), **kwargs)
 
-    def get_value(self, var, cast=None,  # pylint: disable=R0913
-                  default=NOTSET, parse_default=False, add_prefix=True):
+    def get_value(self, var, cast=None, default=NOTSET, parse_default=False):
         """Return value for given environment variable.
 
-        - Expand variables referenced as ``$VAR`` or ``${VAR}``.
-        - Detect infinite recursion in expansion (self-reference).
-
         :param str var:
             Name of variable.
         :param collections.abc.Callable or None cast:
@@ -367,33 +354,15 @@ def get_value(self, var, cast=None,  # pylint: disable=R0913
              If var not present in environ, return this instead.
         :param bool parse_default:
             Force to parse default.
-        :param bool add_prefix:
-            Whether to add prefix to variable name.
         :returns: Value from environment or default (if set).
         :rtype: typing.IO[typing.Any]
         """
-        var_name = f'{self.prefix}{var}' if add_prefix else var
-        if not hasattr(self._local, 'vars'):
-            self._local.vars = set()
-        if var_name in self._local.vars:
-            error_msg = f"Environment variable '{var_name}' recursively "\
-                        "references itself (eventually)"
-            raise ImproperlyConfigured(error_msg)
-
-        self._local.vars.add(var_name)
-        try:
-            return self._get_value(
-                var_name, cast=cast, default=default,
-                parse_default=parse_default)
-        finally:
-            self._local.vars.remove(var_name)
-
-    def _get_value(self, var_name, cast=None, default=NOTSET,
-                   parse_default=False):
+
         logger.debug(
             "get '%s' casted as '%s' with default '%s'",
-            var_name, cast, default)
+            var, cast, default)
 
+        var_name = f'{self.prefix}{var}'
         if var_name in self.scheme:
             var_info = self.scheme[var_name]
 
@@ -419,37 +388,26 @@ def _get_value(self, var_name, cast=None, default=NOTSET,
             value = self.ENVIRON[var_name]
         except KeyError as exc:
             if default is self.NOTSET:
-                error_msg = f'Set the {var_name} environment variable'
+                error_msg = f'Set the {var} environment variable'
                 raise ImproperlyConfigured(error_msg) from exc
 
             value = default
 
-        # Expand variables
-        if isinstance(value, (bytes, str)) and var_name not in NOT_EXPANDED:
-            def repl(match_):
-                return self.get_value(
-                    match_.group('name'), cast=cast, default=default,
-                    parse_default=parse_default, add_prefix=False)
-
-            is_bytes = isinstance(value, bytes)
-            if is_bytes:
-                value = value.decode('utf-8')
-            value = self.VAR.sub(repl, value)
-            value = expandvars(value)
-            if is_bytes:
-                value = value.encode('utf-8')
-
         # Resolve any proxied values
         prefix = b'$' if isinstance(value, bytes) else '$'
         escape = rb'\$' if isinstance(value, bytes) else r'\$'
+        if hasattr(value, 'startswith') and value.startswith(prefix):
+            value = value.lstrip(prefix)
+            value = self.get_value(value, cast=cast, default=default)
 
         if self.escape_proxy and hasattr(value, 'replace'):
             value = value.replace(escape, prefix)
 
         # Smart casting
-        if self.smart_cast and cast is None and default is not None \
-                and not isinstance(default, NoValue):
-            cast = type(default)
+        if self.smart_cast:
+            if cast is None and default is not None and \
+                    not isinstance(default, NoValue):
+                cast = type(default)
 
         value = None if default is None and value == '' else value