[ruff] Mark autofix for RUF052 as always unsafe (#14824)

Author: AlexWaygood

crates/ruff_linter/src/rules/ruff/rules/used_dummy_variable.rs

@@ -16,8 +16,6 @@ use crate::{checkers::ast::Checker, renamer::Renamer};
 /// By default, "dummy variables" are any variables with names that start with leading
 /// underscores. However, this is customisable using the [`lint.dummy-variable-rgx`] setting).
 ///
-/// Dunder variables are ignored by this rule, as are variables named `_`.
-///
 /// ## Why is this bad?
 /// Marking a variable with a leading underscore conveys that it is intentionally unused within the function or method.
 /// When these variables are later referenced in the code, it causes confusion and potential misunderstandings about
@@ -27,18 +25,25 @@ use crate::{checkers::ast::Checker, renamer::Renamer};
 /// Sometimes leading underscores are used to avoid variables shadowing other variables, Python builtins, or Python
 /// keywords. However, [PEP 8] recommends to use trailing underscores for this rather than leading underscores.
 ///
+/// Dunder variables are ignored by this rule, as are variables named `_`.
+/// Only local variables in function scopes are flagged by the rule.
+///
 /// ## Example
 /// ```python
 /// def function():
 ///     _variable = 3
-///     return _variable + 1
+///     # important: avoid shadowing the builtin `id()` function!
+///     _id = 4
+///     return _variable + _id
 /// ```
 ///
 /// Use instead:
 /// ```python
 /// def function():
 ///     variable = 3
-///     return variable + 1
+///     # important: avoid shadowing the builtin `id()` function!
+///     id_ = 4
+///     return variable + id_
 /// ```
 ///
 /// ## Fix availability
@@ -47,6 +52,16 @@ use crate::{checkers::ast::Checker, renamer::Renamer};
 /// would not shadow any other known variables already accessible from the scope
 /// in which the variable is defined.
 ///
+/// ## Fix safety
+/// This rule's fix is marked as unsafe.
+///
+/// For this rule's fix, Ruff renames the variable and fixes up all known references to
+/// it so they point to the renamed variable. However, some renamings also require other
+/// changes such as different arguments to constructor calls or alterations to comments.
+/// Ruff is aware of some of these cases: `_T = TypeVar("_T")` will be fixed to
+/// `T = TypeVar("T")` if the `_T` binding is flagged by this rule. However, in general,
+/// cases like these are hard to detect and hard to automatically fix.
+///
 /// ## Options
 /// - [`lint.dummy-variable-rgx`]
 ///
@@ -146,7 +161,7 @@ pub(crate) fn used_dummy_variable(checker: &Checker, binding: &Binding) -> Optio
         if let Some(fix) = get_possible_fix(name, shadowed_kind, binding.scope, checker) {
             diagnostic.try_set_fix(|| {
                 Renamer::rename(name, &fix, scope, semantic, checker.stylist())
-                    .map(|(edit, rest)| Fix::safe_edits(edit, rest))
+                    .map(|(edit, rest)| Fix::unsafe_edits(edit, rest))
             });
         }
     }

crates/ruff_linter/src/rules/ruff/snapshots/ruff_linter__rules__ruff__tests__RUF052_RUF052.py.snap

@@ -11,7 +11,7 @@ RUF052.py:77:9: RUF052 [*] Local dummy variable `_var` is accessed
    |
    = help: Remove leading underscores
 
-ℹ Safe fix
+ℹ Unsafe fix
 74 74 | 
 75 75 | class Class_:
 76 76 |     def fun(self):
@@ -32,7 +32,7 @@ RUF052.py:84:5: RUF052 [*] Local dummy variable `_list` is accessed
    |
    = help: Prefer using trailing underscores to avoid shadowing a built-in
 
-ℹ Safe fix
+ℹ Unsafe fix
 81 81 |     return _var
 82 82 | 
 83 83 | def fun():
@@ -54,7 +54,7 @@ RUF052.py:91:5: RUF052 [*] Local dummy variable `_x` is accessed
    |
    = help: Prefer using trailing underscores to avoid shadowing a variable
 
-ℹ Safe fix
+ℹ Unsafe fix
 88 88 | 
 89 89 | def fun():
 90 90 |     global x
@@ -77,7 +77,7 @@ RUF052.py:98:5: RUF052 [*] Local dummy variable `_x` is accessed
     |
     = help: Prefer using trailing underscores to avoid shadowing a variable
 
-ℹ Safe fix
+ℹ Unsafe fix
 95  95  |   x = "outer"
 96  96  |   def bar():
 97  97  |     nonlocal x
@@ -99,7 +99,7 @@ RUF052.py:105:5: RUF052 [*] Local dummy variable `_x` is accessed
     |
     = help: Prefer using trailing underscores to avoid shadowing a variable
 
-ℹ Safe fix
+ℹ Unsafe fix
 102 102 | 
 103 103 | def fun():
 104 104 |     x = "local"
@@ -160,7 +160,7 @@ RUF052.py:138:5: RUF052 [*] Local dummy variable `_P` is accessed
     |
     = help: Remove leading underscores
 
-ℹ Safe fix
+ℹ Unsafe fix
 135 135 |     from enum import Enum
 136 136 |     from collections import namedtuple
 137 137 | 
@@ -186,7 +186,7 @@ RUF052.py:139:5: RUF052 [*] Local dummy variable `_T` is accessed
     |
     = help: Remove leading underscores
 
-ℹ Safe fix
+ℹ Unsafe fix
 136 136 |     from collections import namedtuple
 137 137 | 
 138 138 |     _P = ParamSpec("_P")
@@ -213,7 +213,7 @@ RUF052.py:140:5: RUF052 [*] Local dummy variable `_NT` is accessed
     |
     = help: Remove leading underscores
 
-ℹ Safe fix
+ℹ Unsafe fix
 137 137 | 
 138 138 |     _P = ParamSpec("_P")
 139 139 |     _T = TypeVar(name="_T", covariant=True, bound=int|str)
@@ -239,7 +239,7 @@ RUF052.py:141:5: RUF052 [*] Local dummy variable `_E` is accessed
     |
     = help: Remove leading underscores
 
-ℹ Safe fix
+ℹ Unsafe fix
 138 138 |     _P = ParamSpec("_P")
 139 139 |     _T = TypeVar(name="_T", covariant=True, bound=int|str)
 140 140 |     _NT = NamedTuple("_NT", [("foo", int)])
@@ -264,7 +264,7 @@ RUF052.py:142:5: RUF052 [*] Local dummy variable `_NT2` is accessed
     |
     = help: Remove leading underscores
 
-ℹ Safe fix
+ℹ Unsafe fix
 139 139 |     _T = TypeVar(name="_T", covariant=True, bound=int|str)
 140 140 |     _NT = NamedTuple("_NT", [("foo", int)])
 141 141 |     _E = Enum("_E", ["a", "b", "c"])
@@ -288,7 +288,7 @@ RUF052.py:143:5: RUF052 [*] Local dummy variable `_NT3` is accessed
     |
     = help: Remove leading underscores
 
-ℹ Safe fix
+ℹ Unsafe fix
 140 140 |     _NT = NamedTuple("_NT", [("foo", int)])
 141 141 |     _E = Enum("_E", ["a", "b", "c"])
 142 142 |     _NT2 = namedtuple("_NT2", ['x', 'y', 'z'])
@@ -310,7 +310,7 @@ RUF052.py:144:5: RUF052 [*] Local dummy variable `_DynamicClass` is accessed
     |
     = help: Remove leading underscores
 
-ℹ Safe fix
+ℹ Unsafe fix
 141 141 |     _E = Enum("_E", ["a", "b", "c"])
 142 142 |     _NT2 = namedtuple("_NT2", ['x', 'y', 'z'])
 143 143 |     _NT3 = namedtuple(typename="_NT3", field_names=['x', 'y', 'z'])
@@ -332,7 +332,7 @@ RUF052.py:145:5: RUF052 [*] Local dummy variable `_NotADynamicClass` is accessed
     |
     = help: Remove leading underscores
 
-ℹ Safe fix
+ℹ Unsafe fix
 142 142 |     _NT2 = namedtuple("_NT2", ['x', 'y', 'z'])
 143 143 |     _NT3 = namedtuple(typename="_NT3", field_names=['x', 'y', 'z'])
 144 144 |     _DynamicClass = type("_DynamicClass", (), {})

crates/ruff_linter/src/rules/ruff/snapshots/ruff_linter__rules__ruff__tests__custom_dummy_var_regexp_preset__RUF052_RUF052.py_1.snap

@@ -11,7 +11,7 @@ RUF052.py:77:9: RUF052 [*] Local dummy variable `_var` is accessed
    |
    = help: Remove leading underscores
 
-ℹ Safe fix
+ℹ Unsafe fix
 74 74 | 
 75 75 | class Class_:
 76 76 |     def fun(self):
@@ -32,7 +32,7 @@ RUF052.py:84:5: RUF052 [*] Local dummy variable `_list` is accessed
    |
    = help: Prefer using trailing underscores to avoid shadowing a built-in
 
-ℹ Safe fix
+ℹ Unsafe fix
 81 81 |     return _var
 82 82 | 
 83 83 | def fun():
@@ -54,7 +54,7 @@ RUF052.py:91:5: RUF052 [*] Local dummy variable `_x` is accessed
    |
    = help: Prefer using trailing underscores to avoid shadowing a variable
 
-ℹ Safe fix
+ℹ Unsafe fix
 88 88 | 
 89 89 | def fun():
 90 90 |     global x
@@ -77,7 +77,7 @@ RUF052.py:98:5: RUF052 [*] Local dummy variable `_x` is accessed
     |
     = help: Prefer using trailing underscores to avoid shadowing a variable
 
-ℹ Safe fix
+ℹ Unsafe fix
 95  95  |   x = "outer"
 96  96  |   def bar():
 97  97  |     nonlocal x
@@ -99,7 +99,7 @@ RUF052.py:105:5: RUF052 [*] Local dummy variable `_x` is accessed
     |
     = help: Prefer using trailing underscores to avoid shadowing a variable
 
-ℹ Safe fix
+ℹ Unsafe fix
 102 102 | 
 103 103 | def fun():
 104 104 |     x = "local"
@@ -160,7 +160,7 @@ RUF052.py:138:5: RUF052 [*] Local dummy variable `_P` is accessed
     |
     = help: Remove leading underscores
 
-ℹ Safe fix
+ℹ Unsafe fix
 135 135 |     from enum import Enum
 136 136 |     from collections import namedtuple
 137 137 | 
@@ -186,7 +186,7 @@ RUF052.py:139:5: RUF052 [*] Local dummy variable `_T` is accessed
     |
     = help: Remove leading underscores
 
-ℹ Safe fix
+ℹ Unsafe fix
 136 136 |     from collections import namedtuple
 137 137 | 
 138 138 |     _P = ParamSpec("_P")
@@ -213,7 +213,7 @@ RUF052.py:140:5: RUF052 [*] Local dummy variable `_NT` is accessed
     |
     = help: Remove leading underscores
 
-ℹ Safe fix
+ℹ Unsafe fix
 137 137 | 
 138 138 |     _P = ParamSpec("_P")
 139 139 |     _T = TypeVar(name="_T", covariant=True, bound=int|str)
@@ -239,7 +239,7 @@ RUF052.py:141:5: RUF052 [*] Local dummy variable `_E` is accessed
     |
     = help: Remove leading underscores
 
-ℹ Safe fix
+ℹ Unsafe fix
 138 138 |     _P = ParamSpec("_P")
 139 139 |     _T = TypeVar(name="_T", covariant=True, bound=int|str)
 140 140 |     _NT = NamedTuple("_NT", [("foo", int)])
@@ -264,7 +264,7 @@ RUF052.py:142:5: RUF052 [*] Local dummy variable `_NT2` is accessed
     |
     = help: Remove leading underscores
 
-ℹ Safe fix
+ℹ Unsafe fix
 139 139 |     _T = TypeVar(name="_T", covariant=True, bound=int|str)
 140 140 |     _NT = NamedTuple("_NT", [("foo", int)])
 141 141 |     _E = Enum("_E", ["a", "b", "c"])
@@ -288,7 +288,7 @@ RUF052.py:143:5: RUF052 [*] Local dummy variable `_NT3` is accessed
     |
     = help: Remove leading underscores
 
-ℹ Safe fix
+ℹ Unsafe fix
 140 140 |     _NT = NamedTuple("_NT", [("foo", int)])
 141 141 |     _E = Enum("_E", ["a", "b", "c"])
 142 142 |     _NT2 = namedtuple("_NT2", ['x', 'y', 'z'])
@@ -310,7 +310,7 @@ RUF052.py:144:5: RUF052 [*] Local dummy variable `_DynamicClass` is accessed
     |
     = help: Remove leading underscores
 
-ℹ Safe fix
+ℹ Unsafe fix
 141 141 |     _E = Enum("_E", ["a", "b", "c"])
 142 142 |     _NT2 = namedtuple("_NT2", ['x', 'y', 'z'])
 143 143 |     _NT3 = namedtuple(typename="_NT3", field_names=['x', 'y', 'z'])
@@ -332,7 +332,7 @@ RUF052.py:145:5: RUF052 [*] Local dummy variable `_NotADynamicClass` is accessed
     |
     = help: Remove leading underscores
 
-ℹ Safe fix
+ℹ Unsafe fix
 142 142 |     _NT2 = namedtuple("_NT2", ['x', 'y', 'z'])
 143 143 |     _NT3 = namedtuple(typename="_NT3", field_names=['x', 'y', 'z'])
 144 144 |     _DynamicClass = type("_DynamicClass", (), {})