Correctly recognize typing_extensions.NewType (#16298)

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fixes #16297.

since the `.+_NAMES` constants in `types.py` are each referenced
multiple times while other examples like this (i.e. a `.+_NAMES`
tuple/set used only once) are inlined, I've inlined this one.

Author: gschaffner

mypy/semanal_newtype.py

@@ -147,7 +147,7 @@ def analyze_newtype_declaration(self, s: AssignmentStmt) -> tuple[str | None, Ca
             and isinstance(s.lvalues[0], NameExpr)
             and isinstance(s.rvalue, CallExpr)
             and isinstance(s.rvalue.callee, RefExpr)
-            and s.rvalue.callee.fullname == "typing.NewType"
+            and (s.rvalue.callee.fullname in ("typing.NewType", "typing_extensions.NewType"))
         ):
             name = s.lvalues[0].name
 

test-data/unit/check-newtype.test

@@ -379,3 +379,10 @@ N = NewType('N', XXX)  # E: Argument 2 to NewType(...) must be subclassable (got
                        # E: Name "XXX" is not defined
 x: List[Union[N, int]]
 [builtins fixtures/list.pyi]
+
+[case testTypingExtensionsNewType]
+# flags: --python-version 3.7
+from typing_extensions import NewType
+N = NewType("N", int)
+x: N
+[builtins fixtures/tuple.pyi]