From c874eddad1ddb0d031fae1d369eee586af872079 Mon Sep 17 00:00:00 2001
From: Ivan Levkivskyi <levkivskyi@gmail.com>
Date: Fri, 25 Aug 2023 20:43:51 +0100
Subject: [PATCH] Use dedicated error; fix Parameters location

---
 mypy/typeanal.py                              | 26 ++++++++++++++++---
 .../unit/check-parameter-specification.test   | 10 +++++++
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/mypy/typeanal.py b/mypy/typeanal.py
index 7da1e0a99602..e29cca09be63 100644
--- a/mypy/typeanal.py
+++ b/mypy/typeanal.py
@@ -465,9 +465,23 @@ def pack_paramspec_args(self, an_args: Sequence[Type]) -> list[Type]:
             # I didn't find this in the PEP, but it sounds reasonable.
             return list(an_args)
         if any(isinstance(a, (Parameters, ParamSpecType)) for a in an_args):
-            # Nested parameter specifications are not allowed.
+            if len(an_args) > 1:
+                first_wrong = next(
+                    arg for arg in an_args if isinstance(arg, (Parameters, ParamSpecType))
+                )
+                self.fail(
+                    "Nested parameter specifications are not allowed",
+                    first_wrong,
+                    code=codes.VALID_TYPE,
+                )
+                return [AnyType(TypeOfAny.from_error)]
             return list(an_args)
-        return [Parameters(an_args, [ARG_POS] * count, [None] * count)]
+        first = an_args[0]
+        return [
+            Parameters(
+                an_args, [ARG_POS] * count, [None] * count, line=first.line, column=first.column
+            )
+        ]
 
     def cannot_resolve_type(self, t: UnboundType) -> None:
         # TODO: Move error message generation to messages.py. We'd first
@@ -508,7 +522,11 @@ def apply_concatenate_operator(self, t: UnboundType) -> Type:
         names: list[str | None] = [None] * len(args)
 
         pre = Parameters(
-            args + pre.arg_types, [ARG_POS] * len(args) + pre.arg_kinds, names + pre.arg_names
+            args + pre.arg_types,
+            [ARG_POS] * len(args) + pre.arg_kinds,
+            names + pre.arg_names,
+            line=t.line,
+            column=t.column,
         )
         return ps.copy_modified(prefix=pre) if isinstance(ps, ParamSpecType) else pre
 
@@ -918,7 +936,7 @@ def visit_type_list(self, t: TypeList) -> Type:
             if params:
                 ts, kinds, names = params
                 # bind these types
-                return Parameters(self.anal_array(ts), kinds, names)
+                return Parameters(self.anal_array(ts), kinds, names, line=t.line, column=t.column)
             else:
                 return AnyType(TypeOfAny.from_error)
         else:
diff --git a/test-data/unit/check-parameter-specification.test b/test-data/unit/check-parameter-specification.test
index 7d92c0800313..257fb9241373 100644
--- a/test-data/unit/check-parameter-specification.test
+++ b/test-data/unit/check-parameter-specification.test
@@ -1754,3 +1754,13 @@ def dec(fn: Callable[P, T]) -> Alias[P, T]: ...  # type: ignore
 f: Any
 dec(f)  # No crash
 [builtins fixtures/paramspec.pyi]
+
+[case testParamSpecErrorNestedParams]
+from typing import Generic
+from typing_extensions import ParamSpec
+
+P = ParamSpec("P")
+class C(Generic[P]): ...
+c: C[int, [int, str], str]  # E: Nested parameter specifications are not allowed
+reveal_type(c)  # N: Revealed type is "__main__.C[Any]"
+[builtins fixtures/paramspec.pyi]