From c7c6c5fde5f7d5f17b41a2e15c16305880508721 Mon Sep 17 00:00:00 2001
From: cherith <315844584+Cherith1222@users.noreply.github.com>
Date: Tue, 6 Oct 2026 11:34:38 +0800
Subject: [PATCH 1/2] Call function signature hooks when checking decorators.

Decorator calls never reached get_function_signature_hook, so a plugin could not adjust that signature the way a normal call can. AI-assisted (Cursor); not yet reviewed.
---
 mypy/checker.py                         | 10 ++++++++++
 test-data/unit/check-custom-plugin.test | 13 +++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/mypy/checker.py b/mypy/checker.py
index 03120d18b073..af16fad5b2ef 100644
--- a/mypy/checker.py
+++ b/mypy/checker.py
@@ -5911,6 +5911,16 @@ def visit_decorator_inner(
                 object_type = self.lookup_type(d.expr)
                 fullname = self.expr_checker.method_fullname(object_type, d.name)
             self.check_for_untyped_decorator(e.func, dec, d)
+            # check_call does not apply signature hooks; do that here, as for other calls.
+            if fullname:
+                dec = self.expr_checker.transform_callee_type(
+                    fullname,
+                    dec,
+                    [temp],
+                    [nodes.ARG_POS],
+                    e,
+                    object_type=object_type,
+                )
             sig, t2 = self.expr_checker.check_call(
                 dec, [temp], [nodes.ARG_POS], e, callable_name=fullname, object_type=object_type
             )
diff --git a/test-data/unit/check-custom-plugin.test b/test-data/unit/check-custom-plugin.test
index 504c15314553..31ac9f851025 100644
--- a/test-data/unit/check-custom-plugin.test
+++ b/test-data/unit/check-custom-plugin.test
@@ -908,6 +908,19 @@ reveal_type(dynamic_signature(b))  # N: Revealed type is "builtins.bytes"
 \[mypy]
 plugins=<ROOT>/test-data/unit/plugins/function_sig_hook.py
 
+[case testFunctionSigHookCalledOnDecorator]
+# flags: --config-file tmp/mypy.ini
+
+def dynamic_signature(arg1: str) -> str: ...
+
+@dynamic_signature
+def f() -> int: ...
+
+reveal_type(f)  # N: Revealed type is "def () -> builtins.int"
+[file mypy.ini]
+\[mypy]
+plugins=<ROOT>/test-data/unit/plugins/function_sig_hook.py
+
 [case testPluginCalledCorrectlyWhenMethodInDecorator]
 # flags: --config-file tmp/mypy.ini
 from typing import TypeVar, Callable

From 0eb0a693c483e6e789751b09636e097179f84809 Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Wed, 7 Oct 2026 07:15:55 +0000
Subject: [PATCH 2/2] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 mypy/checker.py | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/mypy/checker.py b/mypy/checker.py
index af16fad5b2ef..f762ad860ca6 100644
--- a/mypy/checker.py
+++ b/mypy/checker.py
@@ -5914,12 +5914,7 @@ def visit_decorator_inner(
             # check_call does not apply signature hooks; do that here, as for other calls.
             if fullname:
                 dec = self.expr_checker.transform_callee_type(
-                    fullname,
-                    dec,
-                    [temp],
-                    [nodes.ARG_POS],
-                    e,
-                    object_type=object_type,
+                    fullname, dec, [temp], [nodes.ARG_POS], e, object_type=object_type
                 )
             sig, t2 = self.expr_checker.check_call(
                 dec, [temp], [nodes.ARG_POS], e, callable_name=fullname, object_type=object_type