Delay astroid_bootstrapping() until instantiating AstroidBuilder

ChangeLog

@@ -17,6 +17,11 @@ Release date: TBA
 
 * Reduce file system access in ``ast_from_file()``.
 
+* Reduce time to ``import astroid`` by delaying ``astroid_bootstrapping()`` until
+  the first instantiation of ``AstroidBuilder``.
+
+  Closes #2161
+
 * Make ``igetattr()`` idempotent. This addresses some reports of varying results
   when running pylint with ``--jobs``.
 
@@ -37,7 +42,7 @@ Release date: TBA
   We have tried to minimize the amount of breaking changes caused by this change
   but some are unavoidable.
 
-* ``infer_call_result`` now shares the same interface across all implemenations. Namely:
+* ``infer_call_result`` now shares the same interface across all implementations. Namely:
   ```python
   def infer_call_result(
                 self,

astroid/brain/brain_builtin_inference.py

@@ -129,12 +129,14 @@ def _extend_builtins(class_transforms):
         transform(builtin_ast[class_name])
 
 
-_extend_builtins(
-    {
-        "bytes": partial(_extend_string_class, code=BYTES_CLASS, rvalue="b''"),
-        "str": partial(_extend_string_class, code=STR_CLASS, rvalue="''"),
-    }
-)
+def on_bootstrap():
+    """Called by astroid_bootstrapping()."""
+    _extend_builtins(
+        {
+            "bytes": partial(_extend_string_class, code=BYTES_CLASS, rvalue="b''"),
+            "str": partial(_extend_string_class, code=STR_CLASS, rvalue="''"),
+        }
+    )
 
 
 def _builtin_filter_predicate(node, builtin_name) -> bool:

astroid/brain/brain_nose.py

@@ -7,13 +7,12 @@
 import re
 import textwrap
 
-import astroid.builder
+from astroid.bases import BoundMethod
 from astroid.brain.helpers import register_module_extender
+from astroid.builder import AstroidBuilder
 from astroid.exceptions import InferenceError
 from astroid.manager import AstroidManager
-
-_BUILDER = astroid.builder.AstroidBuilder(AstroidManager())
-
+from astroid.nodes import List, Module
 
 CAPITALS = re.compile("([A-Z])")
 
@@ -24,7 +23,7 @@ def _pep8(name, caps=CAPITALS):
 
 def _nose_tools_functions():
     """Get an iterator of names and bound methods."""
-    module = _BUILDER.string_build(
+    module = AstroidBuilder().string_build(
         textwrap.dedent(
             """
     import unittest
@@ -42,10 +41,10 @@ class Test(unittest.TestCase):
     for method in case.methods():
         if method.name.startswith("assert") and "_" not in method.name:
             pep8_name = _pep8(method.name)
-            yield pep8_name, astroid.BoundMethod(method, case)
+            yield pep8_name, BoundMethod(method, case)
         if method.name == "assertEqual":
             # nose also exports assert_equals.
-            yield "assert_equals", astroid.BoundMethod(method, case)
+            yield "assert_equals", BoundMethod(method, case)
 
 
 def _nose_tools_transform(node):
@@ -55,7 +54,7 @@ def _nose_tools_transform(node):
 
 def _nose_tools_trivial_transform():
     """Custom transform for the nose.tools module."""
-    stub = _BUILDER.string_build("""__all__ = []""")
+    stub = AstroidBuilder().string_build("""__all__ = []""")
     all_entries = ["ok_", "eq_"]
 
     for pep8_name, method in _nose_tools_functions():
@@ -65,7 +64,7 @@ def _nose_tools_trivial_transform():
     # Update the __all__ variable, since nose.tools
     # does this manually with .append.
     all_assign = stub["__all__"].parent
-    all_object = astroid.List(all_entries)
+    all_object = List(all_entries)
     all_object.parent = all_assign
     all_assign.value = all_object
     return stub
@@ -75,5 +74,5 @@ def _nose_tools_trivial_transform():
     AstroidManager(), "nose.tools.trivial", _nose_tools_trivial_transform
 )
 AstroidManager().register_transform(
-    astroid.Module, _nose_tools_transform, lambda n: n.name == "nose.tools"
+    Module, _nose_tools_transform, lambda n: n.name == "nose.tools"
 )

astroid/builder.py

@@ -69,6 +69,8 @@ def __init__(
     ) -> None:
         super().__init__(manager)
         self._apply_transforms = apply_transforms
+        if not raw_building.InspectBuilder.bootstrapped:
+            raw_building._astroid_bootstrapping()
 
     def module_build(
         self, module: types.ModuleType, modname: str | None = None

astroid/raw_building.py

@@ -427,6 +427,8 @@ class InspectBuilder:
     FunctionDef and ClassDef nodes and some others as guessed.
     """
 
+    bootstrapped: bool = False
+
     def __init__(self, manager_instance: AstroidManager | None = None) -> None:
         self._manager = manager_instance or AstroidManager()
         self._done: dict[types.ModuleType | type, nodes.Module | nodes.ClassDef] = {}
@@ -725,5 +727,11 @@ def _astroid_bootstrapping() -> None:
             builder.object_build(klass, _type)
             astroid_builtin[_type.__name__] = klass
 
+    InspectBuilder.bootstrapped = True
+
+    # pylint: disable-next=import-outside-toplevel
+    from astroid.brain.brain_builtin_inference import on_bootstrap
 
-_astroid_bootstrapping()
+    # Instantiates an AstroidBuilder(), which is where
+    # InspectBuilder.bootstrapped is checked, so place after bootstrapped=True.
+    on_bootstrap()