Fix abstract-class-instantiated false positive when class defines __new__ method.

Closes #3060

Author: clavedeluna

doc/whatsnew/fragments/3060.false_positive

@@ -0,0 +1,3 @@
+Fix ``abstract-class-instantiated`` false positive when class defines ``__new__`` method.
+
+Closes #3060

pylint/checkers/base/basic_error_checker.py

@@ -17,7 +17,7 @@
 from pylint.checkers import utils
 from pylint.checkers.base.basic_checker import _BasicChecker
 from pylint.checkers.utils import infer_all
-from pylint.interfaces import HIGH
+from pylint.interfaces import HIGH, INFERENCE
 
 ABC_METACLASSES = {"_py_abc.ABCMeta", "abc.ABCMeta"}  # Python 3.7+,
 # List of methods which can be redefined
@@ -78,6 +78,38 @@ def _has_abstract_methods(node: nodes.ClassDef) -> bool:
     return len(utils.unimplemented_abstract_methods(node)) > 0
 
 
+def _new_correctly_implemented(node: nodes.ClassDef) -> bool:
+    """Check if node implements `__new__`.
+
+    If `__new__` is implemented, check if it calls `super().__new__(cls)`.
+    """
+    if "__new__" not in node.locals:
+        return False
+
+    new = next(node.igetattr("__new__"))
+    if not isinstance(new, astroid.UnboundMethod):
+        return False
+
+    calls = new.nodes_of_class(
+        nodes.Call, skip_klass=(nodes.FunctionDef, nodes.ClassDef)
+    )
+    for call in calls:
+        if not isinstance(call.func, nodes.Attribute):
+            continue
+        if call.func.attrname != "__new__":
+            continue
+
+        super_call = utils.safe_infer(call.func.expr)
+        if not isinstance(super_call, astroid.objects.Super):
+            continue
+
+        # `__new__` calls `super().__new__(cls)`.
+        return False
+
+    # If we get to this point, it means `__new__` has no calls to `super().__new__(cls)`.
+    return True
+
+
 def redefined_by_decorator(node: nodes.FunctionDef) -> bool:
     """Return True if the object is a method redefined via decorator.
 
@@ -446,7 +478,6 @@ def _check_inferred_class_is_abstract(
             # body, we're expecting that it knows what it is doing.
             return
 
-        # __init__ was called
         abstract_methods = _has_abstract_methods(inferred)
 
         if not abstract_methods:
@@ -467,8 +498,16 @@ def _check_inferred_class_is_abstract(
             return
 
         if metaclass.qname() in ABC_METACLASSES:
+            if _new_correctly_implemented(inferred):
+                # A class that implements `__new__` without calling `super().__new__(cls)`
+                # should not emit the message.
+                return
+
             self.add_message(
-                "abstract-class-instantiated", args=(inferred.name,), node=node
+                "abstract-class-instantiated",
+                args=(inferred.name,),
+                node=node,
+                confidence=INFERENCE,
             )
 
     def _check_yield_outside_func(self, node: nodes.Yield) -> None:

tests/functional/a/abstract/abstract_class_instantiated.py

@@ -9,6 +9,7 @@
 import abc
 import weakref
 from lala import Bala
+import pandas as pd
 
 
 class GoodClass(metaclass=abc.ABCMeta):
@@ -141,3 +142,42 @@ def test(self):
 def main_two():
     """ do nothing """
     BadClassTwo() # [abstract-class-instantiated]
+
+
+# Testcase from https://github.com/PyCQA/pylint/issues/3060
+with pd.ExcelWriter("demo.xlsx") as writer:
+    print(writer)
+
+class GoodWithNew(metaclass=abc.ABCMeta):
+    def __new__(cls):
+        pass
+
+    @property
+    @abc.abstractmethod
+    def sheets(self):
+        """sheets."""
+
+    @property
+    @abc.abstractmethod
+    def book(self):
+        """book."""
+
+test = GoodWithNew()
+
+
+class BadWithNew(metaclass=abc.ABCMeta):
+    def __new__(cls):
+        print("Test.__new__")
+        return super().__new__(cls)
+
+    @property
+    @abc.abstractmethod
+    def sheets(self):
+        """sheets."""
+
+    @property
+    @abc.abstractmethod
+    def book(self):
+        """book."""
+
+test = BadWithNew()  # [abstract-class-instantiated]

tests/functional/a/abstract/abstract_class_instantiated.txt

@@ -1,6 +1,7 @@
-abstract-class-instantiated:108:4:108:27:main:Abstract class 'BadMroAbstractMethods' with abstract methods instantiated:UNDEFINED
-abstract-class-instantiated:109:4:109:14:main:Abstract class 'BadClass' with abstract methods instantiated:UNDEFINED
-abstract-class-instantiated:110:4:110:20:main:Abstract class 'SecondBadClass' with abstract methods instantiated:UNDEFINED
-abstract-class-instantiated:111:4:111:19:main:Abstract class 'ThirdBadClass' with abstract methods instantiated:UNDEFINED
-abstract-class-instantiated:128:4:128:20:main2:Abstract class 'FourthBadClass' with abstract methods instantiated:UNDEFINED
-abstract-class-instantiated:143:4:143:17:main_two:Abstract class 'BadClassTwo' with abstract methods instantiated:UNDEFINED
+abstract-class-instantiated:109:4:109:27:main:Abstract class 'BadMroAbstractMethods' with abstract methods instantiated:INFERENCE
+abstract-class-instantiated:110:4:110:14:main:Abstract class 'BadClass' with abstract methods instantiated:INFERENCE
+abstract-class-instantiated:111:4:111:20:main:Abstract class 'SecondBadClass' with abstract methods instantiated:INFERENCE
+abstract-class-instantiated:112:4:112:19:main:Abstract class 'ThirdBadClass' with abstract methods instantiated:INFERENCE
+abstract-class-instantiated:129:4:129:20:main2:Abstract class 'FourthBadClass' with abstract methods instantiated:INFERENCE
+abstract-class-instantiated:144:4:144:17:main_two:Abstract class 'BadClassTwo' with abstract methods instantiated:INFERENCE
+abstract-class-instantiated:183:7:183:19::Abstract class 'BadWithNew' with abstract methods instantiated:INFERENCE