From 0a2846f29d4c2a0244f5d64f858644263dbed33c Mon Sep 17 00:00:00 2001
From: Kai Harder <kai.harder@sap.com>
Date: Mon, 23 Feb 2026 10:42:58 +0000
Subject: [PATCH] Add FTP140

---
 _flake8_tergeo/checks/ast_call.py     | 22 ++++++++++++++++++++++
 docs/checks.md                        |  5 +++++
 news/+e471e45f.feature.md             |  1 +
 tests/checks/test_ast_call.py         | 21 +++++++++++++++++++++
 tests/checks/test_ast_call/ftp140.txt |  8 ++++++++
 5 files changed, 57 insertions(+)
 create mode 100644 news/+e471e45f.feature.md
 create mode 100644 tests/checks/test_ast_call/ftp140.txt

diff --git a/_flake8_tergeo/checks/ast_call.py b/_flake8_tergeo/checks/ast_call.py
index 04dca78..14158f2 100644
--- a/_flake8_tergeo/checks/ast_call.py
+++ b/_flake8_tergeo/checks/ast_call.py
@@ -108,6 +108,7 @@ def check_call(node: ast.Call) -> IssueGenerator:
     yield from _check_type_none_in_isinstance(node)
     yield from _check_mock_builtins_open(node)
     yield from _check_sys_trace_functions(node)
+    yield from _check_utf_8_encoding(node)
 
 
 def _check_os_walk(node: ast.Call) -> IssueGenerator:
@@ -867,3 +868,24 @@ def _check_sys_trace_functions(node: ast.Call) -> IssueGenerator:
         issue_number="138",
         message=f"Trace function {name} should not be called.",
     )
+
+
+def _check_utf_8_encoding(node: ast.Call) -> IssueGenerator:
+    if get_python_version() < (3, 15):
+        return
+    for keyword in node.keywords:
+        if (
+            keyword.arg == "encoding"
+            and is_constant_node(keyword.value, str)
+            and cast(str, keyword.value.value).lower() == "utf-8"
+        ):
+            yield Issue(
+                line=node.lineno,
+                column=node.col_offset,
+                issue_number="140",
+                message=(
+                    "UTF-8 encoding is the default in Python 3.15 and does not need to be "
+                    "specified. Remove the encoding argument or specify a different encoding if "
+                    "needed."
+                ),
+            )
diff --git a/docs/checks.md b/docs/checks.md
index d174408..163a521 100644
--- a/docs/checks.md
+++ b/docs/checks.md
@@ -619,6 +619,11 @@ Finds calls of `sys` trace functions like `sys.settrace`.
 Checks if `profile` or `cProfile` are imported as with python 3.15 `profiling.tracing` should be used.
 The check is only active for python 3.15 and onwards.
 
+## FTP140
+Checks if `encoding="UTF-8"` is used in any function call as UTF-8 is the default encoding
+starting with python 3.15.
+The check is only active for python 3.15 and onwards.
+
 ## FTP200
 Find calls of `flask.abort` and `werkzeug.exceptions.abort`.
 Instead of calling this helper function raise the appropriate exception directly
diff --git a/news/+e471e45f.feature.md b/news/+e471e45f.feature.md
new file mode 100644
index 0000000..1be7eaf
--- /dev/null
+++ b/news/+e471e45f.feature.md
@@ -0,0 +1 @@
+FTP140 which can find unnecessary UTF-8 encodings
diff --git a/tests/checks/test_ast_call.py b/tests/checks/test_ast_call.py
index 9675d0f..fa623ec 100644
--- a/tests/checks/test_ast_call.py
+++ b/tests/checks/test_ast_call.py
@@ -250,6 +250,14 @@
     issue_number="FTP138",
     message="Trace function {func} should not be called.",
 )
+FTP140 = partial(
+    Issue,
+    issue_number="FTP140",
+    message=(
+        "UTF-8 encoding is the default in Python 3.15 and does not need to be specified. "
+        "Remove the encoding argument or specify a different encoding if needed."
+    ),
+)
 
 
 def FTP073(  # pylint:disable=invalid-name
@@ -1104,3 +1112,16 @@ def test(self, runner: Flake8RunnerFixture, imp: str, func: str) -> None:
             filename="ftp138.txt", issue_number="FTP138", imp=imp, func=func
         )
         assert results == [FTP138(line=9, column=1, func=func)]
+
+
+@pytest.mark.parametrize(
+    "python_version,find_by_version", [("3.10.0", False), ("3.15.1", True)]
+)
+def test_ftp140(
+    runner: Flake8RunnerFixture, python_version: str, find_by_version: bool
+) -> None:
+    assert runner(
+        filename="ftp140.txt",
+        issue_number="FTP140",
+        args=("--ftp-python-version", python_version),
+    ) == ([FTP140(line=8, column=1)] if find_by_version else [])
diff --git a/tests/checks/test_ast_call/ftp140.txt b/tests/checks/test_ast_call/ftp140.txt
new file mode 100644
index 0000000..8685f65
--- /dev/null
+++ b/tests/checks/test_ast_call/ftp140.txt
@@ -0,0 +1,8 @@
+# code without issues
+x()
+x = 1
+x(env="utf-8")
+foo(encoding="utf-16")
+
+# code with issues
+foo(encoding="utf-8")