refactor: Make the app argument for BuildEnvironment required

At present, some attributes of env object are considered as optional
because they have been initialized by None on the constructor.  But
they have always been fullfilled actually.

To be clear the type hints of the env object, this makes the `app`
argument for the BuildEnvironment class required.  It can ensure the
attributes of env object are not optional.

CHANGES

@@ -12,6 +12,8 @@ Incompatible changes
 Deprecated
 ----------
 
+* The ``app`` argument of ``sphinx.environment.BuildEnvironment`` becomes
+  required
 * ``sphinx.application.Sphinx.html_theme``
 * ``sphinx.util.docstrings.extract_metadata()``
 

doc/extdev/deprecated.rst

@@ -22,6 +22,11 @@ The following is a list of deprecated interfaces.
      - (will be) Removed
      - Alternatives
 
+   * - The optional argument ``app`` for ``sphinx.environment.BuildEnvironment``
+     - 4.1
+     - 6.0
+     - The required argument
+
    * - ``sphinx.application.Sphinx.html_theme``
      - 4.1
      - 6.0

sphinx/application.py

@@ -300,8 +300,7 @@ class Sphinx:
     def _init_env(self, freshenv: bool) -> None:
         filename = path.join(self.doctreedir, ENV_PICKLE_FILENAME)
         if freshenv or not os.path.exists(filename):
-            self.env = BuildEnvironment()
-            self.env.setup(self)
+            self.env = BuildEnvironment(self)
             self.env.find_files(self.config, self.builder)
         else:
             try:

sphinx/environment/__init__.py

@@ -10,6 +10,7 @@
 
 import os
 import pickle
+import warnings
 from collections import defaultdict
 from copy import copy
 from datetime import datetime
@@ -22,6 +23,7 @@ from docutils.nodes import Node
 
 from sphinx import addnodes
 from sphinx.config import Config
+from sphinx.deprecation import RemovedInSphinx60Warning
 from sphinx.domains import Domain
 from sphinx.environment.adapters.toctree import TocTree
 from sphinx.errors import BuildEnvironmentError, DocumentError, ExtensionError, SphinxError
@@ -181,6 +183,9 @@ class BuildEnvironment:
         # set up environment
         if app:
             self.setup(app)
+        else:
+            warnings.warn("The 'app' argument for BuildEnvironment() becomes required now.",
+                          RemovedInSphinx60Warning, stacklevel=2)
 
     def __getstate__(self) -> Dict:
         """Obtains serializable data for pickling."""

sphinx/ext/autosummary/__init__.py

@@ -80,7 +80,9 @@ from sphinx.ext.autodoc.directive import DocumenterBridge, Options
 from sphinx.ext.autodoc.importer import import_module
 from sphinx.ext.autodoc.mock import mock
 from sphinx.locale import __
+from sphinx.project import Project
 from sphinx.pycode import ModuleAnalyzer, PycodeError
+from sphinx.registry import SphinxComponentRegistry
 from sphinx.util import logging, rst
 from sphinx.util.docutils import (NullReporter, SphinxDirective, SphinxRole, new_document,
                                   switch_source_input)
@@ -168,13 +170,24 @@ def autosummary_table_visit_html(self: HTMLTranslator, node: autosummary_table)
 _app: Sphinx = None
 
 
+class FakeApplication:
+    def __init__(self):
+        self.doctreedir = None
+        self.events = None
+        self.extensions = {}
+        self.srcdir = None
+        self.config = Config()
+        self.project = Project(None, None)
+        self.registry = SphinxComponentRegistry()
+
+
 class FakeDirective(DocumenterBridge):
     def __init__(self) -> None:
         settings = Struct(tab_width=8)
         document = Struct(settings=settings)
-        env = BuildEnvironment()
-        env.config = Config()
-        env.config.add('autodoc_class_signature', 'mixed', True, None)
+        app = FakeApplication()
+        app.config.add('autodoc_class_signature', 'mixed', True, None)
+        env = BuildEnvironment(app)  # type: ignore
         state = Struct(document=document)
         super().__init__(env, None, Options(), 0, state)