gh-123339: Fix cases of inconsistency of __module__ and __firstlineno__ in classes

* Setting the __module__ attribute for a class now removes the
  __firstlineno__ item from the type's dict.
* The _collections_abc and _pydecimal modules now completely replace the
  collections.abc and decimal modules after importing the latters. This
  allows to get the source of classes and functions defined in these
  modules.
* inspect.findsource() now checks whether the first line number for a
  class is out of bound.

Author: serhiy-storchaka

Doc/reference/datamodel.rst

@@ -1008,6 +1008,7 @@ Special attributes:
 
    :attr:`__firstlineno__`
       The line number of the first line of the class definition, including decorators.
+      Setting :attr:`__module__` removes :attr:`__firstlineno__`.
 
 
 Class instances

Lib/collections/abc.py

@@ -1,3 +1,3 @@
-from _collections_abc import *
-from _collections_abc import __all__  # noqa: F401
-from _collections_abc import _CallableGenericAlias  # noqa: F401
+import _collections_abc
+import sys
+sys.modules[__name__] = _collections_abc

Lib/decimal.py

@@ -103,6 +103,7 @@
     from _decimal import __version__  # noqa: F401
     from _decimal import __libmpdec_version__  # noqa: F401
 except ImportError:
-    from _pydecimal import *
-    from _pydecimal import __version__  # noqa: F401
-    from _pydecimal import __libmpdec_version__  # noqa: F401
+    import _pydecimal
+    import sys
+    _pydecimal.__doc__ = __doc__
+    sys.modules[__name__] = _pydecimal

Lib/inspect.py

@@ -970,10 +970,12 @@ def findsource(object):
 
     if isclass(object):
         try:
-            firstlineno = vars(object)['__firstlineno__']
+            lnum = vars(object)['__firstlineno__'] - 1
         except (TypeError, KeyError):
             raise OSError('source code not available')
-        return lines, firstlineno - 1
+        if lnum >= len(lines):
+            raise OSError('lineno is out of bounds')
+        return lines, lnum
 
     if ismethod(object):
         object = object.__func__

Lib/test/test_builtin.py

@@ -2607,6 +2607,7 @@ def test_new_type(self):
         self.assertEqual(A.__module__, __name__)
         self.assertEqual(A.__bases__, (object,))
         self.assertIs(A.__base__, object)
+        self.assertNotIn('__firstlineno__', A.__dict__)
         x = A()
         self.assertIs(type(x), A)
         self.assertIs(x.__class__, A)
@@ -2685,6 +2686,17 @@ def test_type_qualname(self):
             A.__qualname__ = b'B'
         self.assertEqual(A.__qualname__, 'D.E')
 
+    def test_type_firstlineno(self):
+        A = type('A', (), {'__firstlineno__': 42})
+        self.assertEqual(A.__name__, 'A')
+        self.assertEqual(A.__module__, __name__)
+        self.assertEqual(A.__dict__['__firstlineno__'], 42)
+        A.__module__ = 'testmodule'
+        self.assertEqual(A.__module__, 'testmodule')
+        self.assertNotIn('__firstlineno__', A.__dict__)
+        A.__firstlineno__ = 43
+        self.assertEqual(A.__dict__['__firstlineno__'], 43)
+
     def test_type_typeparams(self):
         class A[T]:
             pass

Lib/test/test_decimal.py

@@ -4379,7 +4379,8 @@ def test_module_attributes(self):
 
         self.assertEqual(C.__version__, P.__version__)
 
-        self.assertEqual(dir(C), dir(P))
+        self.assertLessEqual(set(dir(C)), set(dir(P)))
+        self.assertEqual([n for n in dir(C) if n[:2] != '__'], sorted(P.__all__))
 
     def test_context_attributes(self):
 

Lib/test/test_inspect/inspect_fodder2.py

@@ -357,3 +357,15 @@ class td354(typing.TypedDict):
 
 # line 358
 td359 = typing.TypedDict('td359', (('x', int), ('y', int)))
+
+import dataclasses
+
+# line 363
+@dataclasses.dataclass
+class dc364:
+    x: int
+    y: int
+
+# line 369
+dc370 = dataclasses.make_dataclass('dc370', (('x', int), ('y', int)))
+dc371 = dataclasses.make_dataclass('dc370', (('x', int), ('y', int)), module=__name__)

Lib/test/test_inspect/test_inspect.py

@@ -835,6 +835,47 @@ class C:
             nonlocal __firstlineno__
         self.assertRaises(OSError, inspect.getsource, C)
 
+class TestGetsourceStdlib(unittest.TestCase):
+    # Test Python implementations of the stdlib modules
+
+    def test_getsource_stdlib_collections_abc(self):
+        import collections.abc
+        lines, lineno = inspect.getsourcelines(collections.abc.Sequence)
+        self.assertEqual(lines[0], 'class Sequence(Reversible, Collection):\n')
+        src = inspect.getsource(collections.abc.Sequence)
+        self.assertEqual(src.splitlines(True), lines)
+
+    def test_getsource_stdlib_tomllib(self):
+        import tomllib
+        self.assertRaises(OSError, inspect.getsource, tomllib.TOMLDecodeError)
+        self.assertRaises(OSError, inspect.getsourcelines, tomllib.TOMLDecodeError)
+
+    def test_getsource_stdlib_abc(self):
+        # Pure Python implementation
+        abc = import_helper.import_fresh_module('abc', blocked=['_abc'])
+        with support.swap_item(sys.modules, 'abc', abc):
+            self.assertRaises(OSError, inspect.getsource, abc.ABCMeta)
+            self.assertRaises(OSError, inspect.getsourcelines, abc.ABCMeta)
+        # With C acceleration
+        import abc
+        try:
+            src = inspect.getsource(abc.ABCMeta)
+            lines, lineno = inspect.getsourcelines(abc.ABCMeta)
+        except OSError:
+            pass
+        else:
+            self.assertEqual(lines[0], '    class ABCMeta(type):\n')
+            self.assertEqual(src.splitlines(True), lines)
+
+    def test_getsource_stdlib_decimal(self):
+        # Pure Python implementation
+        decimal = import_helper.import_fresh_module('decimal', blocked=['_decimal'])
+        with support.swap_item(sys.modules, 'decimal', decimal):
+            src = inspect.getsource(decimal.Decimal)
+            lines, lineno = inspect.getsourcelines(decimal.Decimal)
+        self.assertEqual(lines[0], 'class Decimal(object):\n')
+        self.assertEqual(src.splitlines(True), lines)
+
 class TestGetsourceInteractive(unittest.TestCase):
     def test_getclasses_interactive(self):
         # bpo-44648: simulate a REPL session;
@@ -947,6 +988,11 @@ def test_typeddict(self):
         self.assertSourceEqual(mod2.td354, 354, 356)
         self.assertRaises(OSError, inspect.getsource, mod2.td359)
 
+    def test_dataclass(self):
+        self.assertSourceEqual(mod2.dc364, 364, 367)
+        self.assertRaises(OSError, inspect.getsource, mod2.dc370)
+        self.assertRaises(OSError, inspect.getsource, mod2.dc371)
+
 class TestBlockComments(GetSourceBase):
     fodderModule = mod
 
@@ -1010,17 +1056,28 @@ def test_findsource_without_filename(self):
             self.assertRaises(IOError, inspect.findsource, co)
             self.assertRaises(IOError, inspect.getsource, co)
 
-    def test_findsource_with_out_of_bounds_lineno(self):
+    def test_findsource_on_func_with_out_of_bounds_lineno(self):
         mod_len = len(inspect.getsource(mod))
         src = '\n' * 2* mod_len + "def f(): pass"
         co = compile(src, mod.__file__, "exec")
         g, l = {}, {}
         eval(co, g, l)
         func = l['f']
         self.assertEqual(func.__code__.co_firstlineno, 1+2*mod_len)
-        with self.assertRaisesRegex(IOError, "lineno is out of bounds"):
+        with self.assertRaisesRegex(OSError, "lineno is out of bounds"):
             inspect.findsource(func)
 
+    def test_findsource_on_class_with_out_of_bounds_lineno(self):
+        mod_len = len(inspect.getsource(mod))
+        src = '\n' * 2* mod_len + "class A: pass"
+        co = compile(src, mod.__file__, "exec")
+        g, l = {'__name__': mod.__name__}, {}
+        eval(co, g, l)
+        cls = l['A']
+        self.assertEqual(cls.__firstlineno__, 1+2*mod_len)
+        with self.assertRaisesRegex(OSError, "lineno is out of bounds"):
+            inspect.findsource(cls)
+
     def test_getsource_on_method(self):
         self.assertSourceEqual(mod2.ClassWithMethod.method, 118, 119)
 

Misc/NEWS.d/next/Core_and_Builtins/2024-09-02-20-36-45.gh-issue-123339.QcmpSs.rst

@@ -0,0 +1,3 @@
+Setting the :attr:`!__module__` attribute for a class now removes the
+``__firstlineno__`` item from the type's dict, so they will no longer be
+inconsistent.

Misc/NEWS.d/next/Library/2024-09-02-20-34-04.gh-issue-123339.czgcSu.rst

@@ -0,0 +1,4 @@
+Fix :func:`inspect.getsource` for classes in :mod:`collections.abc` and
+:mod:`decimal` (for pure Python implementation) modules.
+:func:`inspect.getcomments` now raises OSError instead of IndexError if the
+``__firstlineno__`` value for a class is out of bound.

Objects/typeobject.c

@@ -1444,6 +1444,9 @@ type_set_module(PyTypeObject *type, PyObject *value, void *context)
     PyType_Modified(type);
 
     PyObject *dict = lookup_tp_dict(type);
+    if (PyDict_Pop(dict, &_Py_ID(__firstlineno__), NULL) < 0) {
+        return -1;
+    }
     return PyDict_SetItem(dict, &_Py_ID(__module__), value);
 }