From 6a1aac8f83670ee918eb9981e046a8dd554df297 Mon Sep 17 00:00:00 2001
From: Ivan Levkivskyi <levkivskyi@gmail.com>
Date: Sat, 6 Sep 2025 01:17:48 +0100
Subject: [PATCH 1/2] Add line number to function cache

---
 mypy/nodes.py                         |  8 ++++++++
 test-data/unit/check-incremental.test | 22 ++++++++++++++++++++--
 test-data/unit/fine-grained.test      | 14 ++++++++++++++
 3 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/mypy/nodes.py b/mypy/nodes.py
index 9cfc61c80b3e..e597fa3490ef 100644
--- a/mypy/nodes.py
+++ b/mypy/nodes.py
@@ -989,6 +989,8 @@ def serialize(self) -> JsonDict:
             ),
             "deprecated": self.deprecated,
             "original_first_arg": self.original_first_arg,
+            "line": self.line,
+            "column": self.column,
         }
 
     @classmethod
@@ -1018,6 +1020,8 @@ def deserialize(cls, data: JsonDict) -> FuncDef:
             else None
         )
         ret.deprecated = data["deprecated"]
+        ret.line = data["line"]
+        ret.column = data["column"]
         # Leave these uninitialized so that future uses will trigger an error
         del ret.arguments
         del ret.max_pos
@@ -1040,6 +1044,8 @@ def write(self, data: Buffer) -> None:
             self.dataclass_transform_spec.write(data)
         write_str_opt(data, self.deprecated)
         write_str_opt(data, self.original_first_arg)
+        write_int(data, self.line)
+        write_int(data, self.column)
 
     @classmethod
     def read(cls, data: Buffer) -> FuncDef:
@@ -1058,6 +1064,8 @@ def read(cls, data: Buffer) -> FuncDef:
             ret.dataclass_transform_spec = DataclassTransformSpec.read(data)
         ret.deprecated = read_str_opt(data)
         ret.original_first_arg = read_str_opt(data)
+        ret.line = read_int(data)
+        ret.column = read_int(data)
         # Leave these uninitialized so that future uses will trigger an error
         del ret.arguments
         del ret.max_pos
diff --git a/test-data/unit/check-incremental.test b/test-data/unit/check-incremental.test
index defe7402730f..241ffbd5e139 100644
--- a/test-data/unit/check-incremental.test
+++ b/test-data/unit/check-incremental.test
@@ -210,6 +210,7 @@ def foo() -> int:
 [out2]
 tmp/mod2.py:4: error: Incompatible return value type (got "str", expected "int")
 
+-- Function line numbers can affect error messages, so should be part of public interface.
 [case testIncrementalInternalScramble]
 import mod1
 
@@ -236,8 +237,8 @@ def bar() -> int:
 
 def baz() -> int:
     return 42
-[rechecked mod2]
-[stale]
+[rechecked mod1, mod2]
+[stale mod2]
 
 [case testIncrementalMethodInterfaceChange]
 import mod1
@@ -6897,3 +6898,20 @@ import does_not_exist
 [builtins fixtures/ops.pyi]
 [out]
 [out2]
+
+[case testCachedUnexpectedKeywordArgument]
+import a
+[file a.py]
+import b
+b.lol(uhhhh=12) # tweak
+[file a.py.2]
+import b
+b.lol(uhhhh=12)
+[file b.py]
+def lol() -> None: pass
+[out]
+tmp/a.py:2: error: Unexpected keyword argument "uhhhh" for "lol"
+tmp/b.py:1: note: "lol" defined here
+[out2]
+tmp/a.py:2: error: Unexpected keyword argument "uhhhh" for "lol"
+tmp/b.py:1: note: "lol" defined here
diff --git a/test-data/unit/fine-grained.test b/test-data/unit/fine-grained.test
index 888b7bc7e97f..693c7b8cbf3a 100644
--- a/test-data/unit/fine-grained.test
+++ b/test-data/unit/fine-grained.test
@@ -5178,6 +5178,20 @@ def g(y: T) -> T:
 a.py:2: error: Unexpected keyword argument "x"
 c.py:4: note: Called function defined here
 
+[case testFineGrainedUnexpectedKeywordArgument]
+import a
+[file a.py]
+import b
+[file a.py.2]
+import b
+b.lol(uhhhh=12)
+[file b.py]
+def lol() -> None: pass
+[out]
+==
+a.py:2: error: Unexpected keyword argument "uhhhh" for "lol"
+b.py:1: note: "lol" defined here
+
 [case testGenericFineCallableInBound]
 import a
 [file a.py]

From cadf7ff60b6a79410789760ec136534a4031785b Mon Sep 17 00:00:00 2001
From: Ivan Levkivskyi <levkivskyi@gmail.com>
Date: Sat, 6 Sep 2025 01:41:09 +0100
Subject: [PATCH 2/2] Update couple more tests

---
 test-data/unit/check-serialize.test | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/test-data/unit/check-serialize.test b/test-data/unit/check-serialize.test
index 03c185a5694b..eda8f7a5d893 100644
--- a/test-data/unit/check-serialize.test
+++ b/test-data/unit/check-serialize.test
@@ -158,7 +158,7 @@ def f(__x: int) -> None: pass
 [out2]
 tmp/a.py:3: error: Argument 1 to "f" has incompatible type "str"; expected "int"
 tmp/a.py:4: error: Unexpected keyword argument "__x" for "f"
-tmp/b.py: note: "f" defined here
+tmp/b.py:1: note: "f" defined here
 
 [case testSerializeArgumentKindsErrors]
 import a
@@ -224,7 +224,7 @@ def f(x: int) -> int: pass
 [out2]
 tmp/a.py:2: note: Revealed type is "builtins.str"
 tmp/a.py:3: error: Unexpected keyword argument "x" for "f"
-tmp/b.py: note: "f" defined here
+tmp/b.py:4: note: "f" defined here
 
 [case testSerializeTypeGuardFunction]
 import a