Minor followups to RUF052

crates/ruff_linter/resources/test/fixtures/ruff/RUF052.py

@@ -14,7 +14,7 @@
 _valid_var_3 = _valid_var_1 + _valid_var_2
 
 def _valid_fun():
-    pass    
+    pass
 
 _valid_fun()
 
@@ -35,7 +35,7 @@ def fun():
 def fun():
     global _x
     _x = "reassigned global"
-    return _x  
+    return _x
 
 class _ValidClass:
     pass
@@ -56,7 +56,7 @@ def _valid_method(self):
 
     def method(arg):
         _valid_unused_var = arg
-        return 
+        return
 
 def fun(x):
     _ = 1
@@ -104,3 +104,28 @@ def fun():
     x = "local"
     _x = "shadows local" # [RUF052]
     return _x
+
+
+GLOBAL_1 = "global 1"
+GLOBAL_1_ = "global 1 with trailing underscore"
+
+def unfixables():
+    _GLOBAL_1 = "foo"
+    # unfixable because the rename would shadow a global variable
+    print(_GLOBAL_1)  # [RUF052]
+
+    local = "local"
+    local_ = "local2"
+
+    # unfixable because the rename would shadow a local variable
+    _local = "local3"  # [RUF052]
+    print(_local)
+
+    def nested():
+        _GLOBAL_1 = "foo"
+        # unfixable because the rename would shadow a global variable
+        print(_GLOBAL_1)  # [RUF052]
+
+        # unfixable because the rename would shadow a variable from the outer function
+        _local = "local4"
+        print(_local)

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

@@ -10,16 +10,19 @@ use ruff_text_size::Ranged;
 use crate::{checkers::ast::Checker, renamer::Renamer};
 
 /// ## What it does
-/// Checks for accesses of local dummy variables, excluding `_` and dunder variables.
+/// Checks for "dummy variables" (variables that are named as if to indicate they are unused)
+/// that are in fact used.
 ///
 /// By default, "dummy variables" are any variables with names that start with leading
-/// underscores. However, this is customisable using the `dummy-variable-rgx` setting).
+/// 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
-/// the code's intention. A variable marked as "unused" being subsequently used suggests oversight or unintentional use.
-/// This detracts from the clarity and maintainability of the codebase.
+/// the code's intention. If a variable marked as "unused" is subsequently used, it suggests that either the variable
+/// could be given a clearer name, or that the code is accidentally making use of the wrong variable.
 ///
 /// 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.
@@ -39,12 +42,14 @@ use crate::{checkers::ast::Checker, renamer::Renamer};
 /// ```
 ///
 /// ## Fix availability
-/// An fix is only available for variables that start with leading underscores.
+/// The rule's fix is only available for variables that start with leading underscores.
+/// It will also only be available if the "obvious" new name for the variable
+/// would not shadow any other known variables already accessible from the scope
+/// in which the variable is defined.
 ///
 /// ## Options
 /// - [`lint.dummy-variable-rgx`]
 ///
-///
 /// [PEP 8]: https://peps.python.org/pep-0008/
 #[derive(ViolationMetadata)]
 pub(crate) struct UsedDummyVariable {
@@ -61,21 +66,18 @@ impl Violation for UsedDummyVariable {
     }
 
     fn fix_title(&self) -> Option<String> {
-        if let Some(shadowed_kind) = self.shadowed_kind {
-            return Some(match shadowed_kind {
-                ShadowedKind::BuiltIn => {
-                    "Prefer using trailing underscores to avoid shadowing a built-in".to_string()
-                }
-                ShadowedKind::Keyword => {
-                    "Prefer using trailing underscores to avoid shadowing a keyword".to_string()
-                }
-                ShadowedKind::Some => {
-                    "Prefer using trailing underscores to avoid shadowing a variable".to_string()
-                }
-                ShadowedKind::None => "Remove leading underscores".to_string(),
-            });
-        }
-        None
+        self.shadowed_kind.map(|kind| match kind {
+            ShadowedKind::BuiltIn => {
+                "Prefer using trailing underscores to avoid shadowing a built-in".to_string()
+            }
+            ShadowedKind::Keyword => {
+                "Prefer using trailing underscores to avoid shadowing a keyword".to_string()
+            }
+            ShadowedKind::Some => {
+                "Prefer using trailing underscores to avoid shadowing a variable".to_string()
+            }
+            ShadowedKind::None => "Remove leading underscores".to_string(),
+        })
     }
 }
 

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

@@ -1,6 +1,5 @@
 ---
 source: crates/ruff_linter/src/rules/ruff/mod.rs
-snapshot_kind: text
 ---
 RUF052.py:77:9: RUF052 [*] Local dummy variable `_var` is accessed
    |
@@ -130,3 +129,44 @@ RUF052.py:105:5: RUF052 [*] Local dummy variable `_x` is accessed
 106     |-    return _x
     105 |+    x_ = "shadows local" # [RUF052]
     106 |+    return x_
+107 107 | 
+108 108 | 
+109 109 | GLOBAL_1 = "global 1"
+
+RUF052.py:113:5: RUF052 Local dummy variable `_GLOBAL_1` is accessed
+    |
+112 | def unfixables():
+113 |     _GLOBAL_1 = "foo"
+    |     ^^^^^^^^^ RUF052
+114 |     # unfixable because the rename would shadow a global variable
+115 |     print(_GLOBAL_1)  # [RUF052]
+    |
+    = help: Prefer using trailing underscores to avoid shadowing a variable
+
+RUF052.py:121:5: RUF052 Local dummy variable `_local` is accessed
+    |
+120 |     # unfixable because the rename would shadow a local variable
+121 |     _local = "local3"  # [RUF052]
+    |     ^^^^^^ RUF052
+122 |     print(_local)
+    |
+    = help: Prefer using trailing underscores to avoid shadowing a variable
+
+RUF052.py:125:9: RUF052 Local dummy variable `_GLOBAL_1` is accessed
+    |
+124 |     def nested():
+125 |         _GLOBAL_1 = "foo"
+    |         ^^^^^^^^^ RUF052
+126 |         # unfixable because the rename would shadow a global variable
+127 |         print(_GLOBAL_1)  # [RUF052]
+    |
+    = help: Prefer using trailing underscores to avoid shadowing a variable
+
+RUF052.py:130:9: RUF052 Local dummy variable `_local` is accessed
+    |
+129 |         # unfixable because the rename would shadow a variable from the outer function
+130 |         _local = "local4"
+    |         ^^^^^^ RUF052
+131 |         print(_local)
+    |
+    = help: Prefer using trailing underscores to avoid shadowing a variable

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

@@ -1,6 +1,5 @@
 ---
 source: crates/ruff_linter/src/rules/ruff/mod.rs
-snapshot_kind: text
 ---
 RUF052.py:77:9: RUF052 [*] Local dummy variable `_var` is accessed
    |
@@ -130,3 +129,44 @@ RUF052.py:105:5: RUF052 [*] Local dummy variable `_x` is accessed
 106     |-    return _x
     105 |+    x_ = "shadows local" # [RUF052]
     106 |+    return x_
+107 107 | 
+108 108 | 
+109 109 | GLOBAL_1 = "global 1"
+
+RUF052.py:113:5: RUF052 Local dummy variable `_GLOBAL_1` is accessed
+    |
+112 | def unfixables():
+113 |     _GLOBAL_1 = "foo"
+    |     ^^^^^^^^^ RUF052
+114 |     # unfixable because the rename would shadow a global variable
+115 |     print(_GLOBAL_1)  # [RUF052]
+    |
+    = help: Prefer using trailing underscores to avoid shadowing a variable
+
+RUF052.py:121:5: RUF052 Local dummy variable `_local` is accessed
+    |
+120 |     # unfixable because the rename would shadow a local variable
+121 |     _local = "local3"  # [RUF052]
+    |     ^^^^^^ RUF052
+122 |     print(_local)
+    |
+    = help: Prefer using trailing underscores to avoid shadowing a variable
+
+RUF052.py:125:9: RUF052 Local dummy variable `_GLOBAL_1` is accessed
+    |
+124 |     def nested():
+125 |         _GLOBAL_1 = "foo"
+    |         ^^^^^^^^^ RUF052
+126 |         # unfixable because the rename would shadow a global variable
+127 |         print(_GLOBAL_1)  # [RUF052]
+    |
+    = help: Prefer using trailing underscores to avoid shadowing a variable
+
+RUF052.py:130:9: RUF052 Local dummy variable `_local` is accessed
+    |
+129 |         # unfixable because the rename would shadow a variable from the outer function
+130 |         _local = "local4"
+    |         ^^^^^^ RUF052
+131 |         print(_local)
+    |
+    = help: Prefer using trailing underscores to avoid shadowing a variable

crates/ruff_linter/src/rules/ruff/snapshots/ruff_linter__rules__ruff__tests__custom_dummy_var_regexp_preset__RUF052_RUF052.py_2.snap

@@ -1,6 +1,5 @@
 ---
 source: crates/ruff_linter/src/rules/ruff/mod.rs
-snapshot_kind: text
 ---
 RUF052.py:21:9: RUF052 Local dummy variable `arg` is accessed
    |
@@ -38,12 +37,12 @@ RUF052.py:57:16: RUF052 Local dummy variable `arg` is accessed
 57 |     def method(arg):
    |                ^^^ RUF052
 58 |         _valid_unused_var = arg
-59 |         return 
+59 |         return
    |
 
 RUF052.py:61:9: RUF052 Local dummy variable `x` is accessed
    |
-59 |         return 
+59 |         return
 60 | 
 61 | def fun(x):
    |         ^ RUF052
@@ -119,3 +118,41 @@ RUF052.py:105:5: RUF052 Local dummy variable `_x` is accessed
 106 |     return _x
     |
     = help: Prefer using trailing underscores to avoid shadowing a variable
+
+RUF052.py:113:5: RUF052 Local dummy variable `_GLOBAL_1` is accessed
+    |
+112 | def unfixables():
+113 |     _GLOBAL_1 = "foo"
+    |     ^^^^^^^^^ RUF052
+114 |     # unfixable because the rename would shadow a global variable
+115 |     print(_GLOBAL_1)  # [RUF052]
+    |
+    = help: Prefer using trailing underscores to avoid shadowing a variable
+
+RUF052.py:121:5: RUF052 Local dummy variable `_local` is accessed
+    |
+120 |     # unfixable because the rename would shadow a local variable
+121 |     _local = "local3"  # [RUF052]
+    |     ^^^^^^ RUF052
+122 |     print(_local)
+    |
+    = help: Prefer using trailing underscores to avoid shadowing a variable
+
+RUF052.py:125:9: RUF052 Local dummy variable `_GLOBAL_1` is accessed
+    |
+124 |     def nested():
+125 |         _GLOBAL_1 = "foo"
+    |         ^^^^^^^^^ RUF052
+126 |         # unfixable because the rename would shadow a global variable
+127 |         print(_GLOBAL_1)  # [RUF052]
+    |
+    = help: Prefer using trailing underscores to avoid shadowing a variable
+
+RUF052.py:130:9: RUF052 Local dummy variable `_local` is accessed
+    |
+129 |         # unfixable because the rename would shadow a variable from the outer function
+130 |         _local = "local4"
+    |         ^^^^^^ RUF052
+131 |         print(_local)
+    |
+    = help: Prefer using trailing underscores to avoid shadowing a variable