loader: remove delayed imports from pymod02_importers

Instead of performing delayed import of modules, add them (and
their depdendencies) to compat.PY3_BASE_MODULES to have them
available during the bootstrap.

PyInstaller/compat.py

@@ -620,11 +620,12 @@ def importlib_load_source(name, pathname):
     return mod_loader.load_module()
 
 
-# Patterns of module names that should be bundled into the base_library.zip.
+# Patterns of module names that should be bundled into the base_library.zip to be available during bootstrap.
+# These modules include direct or indirect dependencies of encodings.* modules. The encodings modules must be
+# recursively included to set the I/O encoding during python startup. Similarly, this list should include
+# modules used by PyInstaller's bootstrap scripts and modules (loader/pyi*.py)
 
 PY3_BASE_MODULES = {
-    # These modules are direct or indirect dependencies of encodings.* modules. encodings modules must be recursively
-    # included to set the I/O encoding during python startup.
     '_collections_abc',
     '_weakrefset',
     'abc',
@@ -633,26 +634,30 @@ def importlib_load_source(name, pathname):
     'copyreg',
     'encodings',
     'enum',
+    'fnmatch',  # dependency of pathlib
     'functools',
     'genericpath',  # dependency of os.path
-    'io',
+    'io',  # used by loader/pymod02_importers.py
     'heapq',
     'keyword',
     'linecache',
     'locale',
     'ntpath',  # dependency of os.path
     'operator',
     'os',
+    'pathlib',  # used by loader/pymod02_importers.py
     'posixpath',  # dependency of os.path
     're',
     'reprlib',
     'sre_compile',
     'sre_constants',
     'sre_parse',
     'stat',  # dependency of os.path
-    'tokenize',  # used by loader/pymod03_importers.py
+    'token',  # depdendency of tokenize
+    'tokenize',  # used by loader/pymod02_importers.py
     'traceback',  # for startup errors
     'types',
+    'urllib',  # dependency of pathlib
     'weakref',
     'warnings',
 }

PyInstaller/loader/pyimod02_importers.py

@@ -13,13 +13,18 @@
 """
 
 # **NOTE** This module is used during bootstrap.
-# Import *ONLY* builtin modules.
+# Import *ONLY* builtin modules or modules that are collected into the base_library.zip archive.
 # List of built-in modules: sys.builtin_module_names
+# List of modules collected into base_library.zip: PyInstaller.compat.PY3_BASE_MODULES
 
 import sys
-import os  # guaranteed to be in baselib
+import os
+import pathlib
+import io
+import tokenize
 
 import _frozen_importlib
+
 from pyimod01_archive import ArchiveReadError, ZlibArchiveReader
 
 SYS_PREFIX = sys._MEIPASS + os.sep
@@ -62,11 +67,6 @@ def _decode_source(source_bytes):
     Based on CPython's implementation of the same functionality:
     https://github.com/python/cpython/blob/3.9/Lib/importlib/_bootstrap_external.py#L679-L688
     """
-    # Local imports to avoid bootstrap issues
-    # NOTE: both modules are listed in compat.PY3_BASE_MODULES and collected into base_library.zip.
-    import io
-    import tokenize
-
     source_bytes_readline = io.BytesIO(source_bytes).readline
     encoding = tokenize.detect_encoding(source_bytes_readline)
     newline_decoder = io.IncrementalNewlineDecoder(decoder=None, translate=True)
@@ -532,7 +532,6 @@ class FrozenResourceReader:
       https://github.com/python/cpython/blob/839d7893943782ee803536a47f1d4de160314f85/Lib/importlib/abc.py#L312
     """
     def __init__(self, importer, name):
-        import pathlib  # Local import to avoid bootstrap issues.
         self.importer = importer
         self.path = pathlib.Path(sys._MEIPASS).joinpath(*name.split('.'))