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String mutations: the two case flips are equivalent wherever the consumer is case-insensitive, and no option turns them off

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@nabi-noor 已经在做这个了。

开始于 2026年9月10日。

  • #579 来自 @nabi-noor —— 未关闭

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难度
4/5
预计耗时
3-5 天
新手友好度
55/100
Issue 类型
功能
描述清晰度
基本清楚
活跃度
活跃
技术栈
python, sqlite
领域
cli, testing-qa, tooling

调研方向

从 operator_string 入口点以及现有的 --disable-mutation-types 和 do_not_mutate_patterns 配置行为开始。使用 example.py、test_example.py 和 pyproject.toml 重现残留的小写和大写变异体，然后添加回归覆盖，证明可以禁用大小写转换而不移除 XX 变异体或索引变异体。

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描述

enhancement good first issue

Disclaimer: AI-drafted, verified by me before filing. I answer follow-ups.

operator_string emits three mutants for every string literal: the literal wrapped in XX, lowercased, and uppercased. Where the literal's consumer is case-insensitive -- SQL, codec names, HTTP header names -- the case flips are equivalent mutants by construction.

Expected: a mutation I cannot kill can be switched off, as --disable-mutation-types did in 2.x (#175, added by #225).
Actual: both case flips survive every run, and the only lever in 3.x, do_not_mutate_patterns, matches whole lines, so it drops the XX mutant on that line too.

They were 25% and 11% of all survivors on two of my codebases: re-read on every run, and nothing to be done about them.

Reproduce -- three files, mutmut 3.7.0, pytest 9.1.1, CPython 3.12.12 
# example.py
import sqlite3


def note_count(db_path: str) -> int:
    con = sqlite3.connect(db_path)
    return con.execute("SELECT COUNT(*) FROM notes").fetchone()[0]

# test_example.py
import sqlite3

from example import note_count


def test_note_count(tmp_path):
    db = tmp_path / "n.db"
    con = sqlite3.connect(db)
    con.execute("CREATE TABLE notes (id int)")
    con.execute("INSERT INTO notes VALUES (1)")
    con.commit()
    con.close()
    assert note_count(str(db)) == 1

# pyproject.toml
[project]
name = "repro"
version = "0"
requires-python = ">=3.11"

[tool.mutmut]
source_paths = ["example.py"]

$ mutmut run
7/7  🎉 5 🫥 0  ⏰ 0  🤔 0  🙁 2  🔇 0  🧙 0

$ mutmut results
    example.x_note_count__mutmut_5: survived
    example.x_note_count__mutmut_6: survived

$ mutmut show example.x_note_count__mutmut_5
# example.x_note_count__mutmut_5: survived
--- example.py
+++ example.py
@@ -1,3 +1,3 @@
 def note_count(db_path: str) -> int:
     con = sqlite3.connect(db_path)
-    return con.execute("SELECT COUNT(*) FROM notes").fetchone()[0]
+    return con.execute("select count(*) from notes").fetchone()[0]

$ mutmut show example.x_note_count__mutmut_6      # the same line, uppercased
+    return con.execute("SELECT COUNT(*) FROM NOTES").fetchone()[0]

SQLite parses either casing and resolves table names case-insensitively, so both mutants are equivalent to the original. The only test that would kill them asserts the query string's exact casing, which tests the literal rather than the behaviour.

What the line pattern costs -- 7 mutants become 2 
[tool.mutmut]
source_paths = ["example.py"]
do_not_mutate_patterns = ["SELECT"]

$ mutmut run
2/2  🎉 2 🫥 0  ⏰ 0  🤔 0  🙁 0  🔇 0  🧙 0

Five of the seven mutants are gone. Two of them, mutant 4 ("XXSELECT COUNT(*) FROM notesXX") and mutant 7 (.fetchone()[1]), are killed by the test as it stands, so the pattern removes working signal in order to remove two mutants that carry none.

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