From 114c423c7f4b6f7df3601ef9d579ecbbf5f38b4a Mon Sep 17 00:00:00 2001
From: Daniil Kalinin <Daniil.Kalinin@jetbrains.com>
Date: Wed, 17 Jun 2026 15:50:19 +0200
Subject: [PATCH] PY-90348 Don't type a parameter as Concatenate/ParamSpec from
 a decorator

(cherry picked from commit 11725b2cbd96eb0d8074f85f4b4cc700a552f6bf)

GitOrigin-RevId: cb38b7a3b094498d94b044f9369889dbb87b9066
---
 .../PyDecoratedFunctionTypeProvider.java       |  6 ++++++
 .../python/types/PyCallableTypeTest.kt         | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/python/python-psi-impl/src/com/jetbrains/python/codeInsight/decorator/PyDecoratedFunctionTypeProvider.java b/python/python-psi-impl/src/com/jetbrains/python/codeInsight/decorator/PyDecoratedFunctionTypeProvider.java
index afde21dd1406..7dc87678f477 100644
--- a/python/python-psi-impl/src/com/jetbrains/python/codeInsight/decorator/PyDecoratedFunctionTypeProvider.java
+++ b/python/python-psi-impl/src/com/jetbrains/python/codeInsight/decorator/PyDecoratedFunctionTypeProvider.java
@@ -20,6 +20,8 @@ import com.jetbrains.python.psi.types.PyCallableParameter;
 import com.jetbrains.python.psi.types.PyCallableType;
 import com.jetbrains.python.psi.types.PyCallableTypeImpl;
 import com.jetbrains.python.psi.types.PyClassType;
+import com.jetbrains.python.psi.types.PyConcatenateType;
+import com.jetbrains.python.psi.types.PyParamSpecType;
 import com.jetbrains.python.psi.types.PySyntheticCallHelper;
 import com.jetbrains.python.psi.types.PyType;
 import com.jetbrains.python.psi.types.PyTypeChecker;
@@ -73,6 +75,10 @@ public final class PyDecoratedFunctionTypeProvider extends PyTypeProviderBase {
       if (paramPos < 0) return null;
 
       var type = ParamHelper.getExpectedTypeForPositionalParam(paramPos, expectedParams, context);
+      // A Concatenate/ParamSpec is a whole parameter list, not a single parameter's type; don't assign it to
+      // one parameter (e.g. `self` under @hybrid_method). Defer to regular inference (PY-90348).
+      if (type instanceof PyConcatenateType || type instanceof PyParamSpecType) return null;
+
       return type != null ? Ref.create(type) : null;
     }
     return null;
diff --git a/python/testSrc/com/jetbrains/python/types/PyCallableTypeTest.kt b/python/testSrc/com/jetbrains/python/types/PyCallableTypeTest.kt
index d7f18526cba3..115188d5ccbd 100644
--- a/python/testSrc/com/jetbrains/python/types/PyCallableTypeTest.kt
+++ b/python/testSrc/com/jetbrains/python/types/PyCallableTypeTest.kt
@@ -736,6 +736,24 @@ class PyCallableTypeTest : PyCodeInsightTestCase() {
                 return x + y
         """,
     )
+
+    @Test
+    @TestFor(issues = ["PY-90348"])
+    fun `Concatenate-typed decorator keeps the receiver type`() = test("""
+      from typing import Any, Callable, Concatenate, ParamSpec, TypeVar
+
+      P = ParamSpec("P")
+      R = TypeVar("R")
+
+      def deco(fn: Callable[Concatenate[Any, P], R]) -> Callable[P, R]: ...
+
+      class C:
+        @deco
+        def m(self, a: int) -> int:
+          expr = self
+      #   └ TYPE Self@C
+          return a
+      """)
   }
 
   @Nested