Extends B002 to detect unary prefix decrement operators

crates/ruff/resources/test/fixtures/flake8_bugbear/B002.py

@@ -1,20 +1,24 @@
 """
 Should emit:
-B002 - on lines 15 and 20
+B002 - on lines 18, 19, and 24
 """
 
 
 def this_is_all_fine(n):
     x = n + 1
     y = 1 + n
     z = +x + y
-    return +z
+    a = n - 1
+    b = 1 - n
+    c = -a - b
+    return +z, -c
 
 
 def this_is_buggy(n):
     x = ++n
-    return x
+    y = --n
+    return x, y
 
 
 def this_is_buggy_too(n):
-    return ++n
+    return ++n, --n

crates/ruff/src/checkers/ast/mod.rs

@@ -3302,8 +3302,10 @@ where
                         check_not_is,
                     );
                 }
-                if self.enabled(Rule::UnaryPrefixIncrement) {
-                    flake8_bugbear::rules::unary_prefix_increment(self, expr, *op, operand);
+                if self.enabled(Rule::UnaryPrefixIncrementDecrement) {
+                    flake8_bugbear::rules::unary_prefix_increment_decrement(
+                        self, expr, *op, operand,
+                    );
                 }
                 if self.enabled(Rule::NegateEqualOp) {
                     flake8_simplify::rules::negation_with_equal_op(self, expr, *op, operand);

crates/ruff/src/codes.rs

@@ -235,7 +235,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Flake8Builtins, "003") => (RuleGroup::Unspecified, rules::flake8_builtins::rules::BuiltinAttributeShadowing),
 
         // flake8-bugbear
-        (Flake8Bugbear, "002") => (RuleGroup::Unspecified, rules::flake8_bugbear::rules::UnaryPrefixIncrement),
+        (Flake8Bugbear, "002") => (RuleGroup::Unspecified, rules::flake8_bugbear::rules::UnaryPrefixIncrementDecrement),
         (Flake8Bugbear, "003") => (RuleGroup::Unspecified, rules::flake8_bugbear::rules::AssignmentToOsEnviron),
         (Flake8Bugbear, "004") => (RuleGroup::Unspecified, rules::flake8_bugbear::rules::UnreliableCallableCheck),
         (Flake8Bugbear, "005") => (RuleGroup::Unspecified, rules::flake8_bugbear::rules::StripWithMultiCharacters),

crates/ruff/src/rules/flake8_bugbear/mod.rs

@@ -42,7 +42,7 @@ mod tests {
     #[test_case(Rule::SetAttrWithConstant, Path::new("B009_B010.py"))]
     #[test_case(Rule::StarArgUnpackingAfterKeywordArg, Path::new("B026.py"))]
     #[test_case(Rule::StripWithMultiCharacters, Path::new("B005.py"))]
-    #[test_case(Rule::UnaryPrefixIncrement, Path::new("B002.py"))]
+    #[test_case(Rule::UnaryPrefixIncrementDecrement, Path::new("B002.py"))]
     #[test_case(Rule::UnintentionalTypeAnnotation, Path::new("B032.py"))]
     #[test_case(Rule::UnreliableCallableCheck, Path::new("B004.py"))]
     #[test_case(Rule::UnusedLoopControlVariable, Path::new("B007.py"))]

crates/ruff/src/rules/flake8_bugbear/rules/mod.rs

@@ -23,7 +23,7 @@ pub(crate) use reuse_of_groupby_generator::*;
 pub(crate) use setattr_with_constant::*;
 pub(crate) use star_arg_unpacking_after_keyword_arg::*;
 pub(crate) use strip_with_multi_characters::*;
-pub(crate) use unary_prefix_increment::*;
+pub(crate) use unary_prefix_increment_decrement::*;
 pub(crate) use unintentional_type_annotation::*;
 pub(crate) use unreliable_callable_check::*;
 pub(crate) use unused_loop_control_variable::*;
@@ -57,7 +57,7 @@ mod reuse_of_groupby_generator;
 mod setattr_with_constant;
 mod star_arg_unpacking_after_keyword_arg;
 mod strip_with_multi_characters;
-mod unary_prefix_increment;
+mod unary_prefix_increment_decrement;
 mod unintentional_type_annotation;
 mod unreliable_callable_check;
 mod unused_loop_control_variable;

crates/ruff/src/rules/flake8_bugbear/rules/unary_prefix_increment_decrement.rs

@@ -0,0 +1,87 @@
+use rustpython_parser::ast::{self, Expr, Ranged, UnaryOp};
+
+use ruff_diagnostics::{Diagnostic, Violation};
+use ruff_macros::{derive_message_formats, violation};
+
+use crate::checkers::ast::Checker;
+
+/// ## What it does
+/// Checks for the attempted use of the unary prefix increment (`++`) or
+/// decrement operator (`--`).
+///
+/// ## Why is this bad?
+/// Python does not support the unary prefix increment or decrement operator.
+/// Writing `++n` is equivalent to `+(+(n))` and writing `--n` is equivalent to
+/// `-(-(n))`. In both cases, it is equivalent to `n`.
+///
+/// ## Example
+/// ```python
+/// ++x
+/// --y
+/// ```
+///
+/// Use instead:
+/// ```python
+/// x += 1
+/// y -= 1
+/// ```
+///
+/// ## References
+/// - [Python documentation: Unary arithmetic and bitwise operations](https://docs.python.org/3/reference/expressions.html#unary-arithmetic-and-bitwise-operations)
+/// - [Python documentation: Augmented assignment statements](https://docs.python.org/3/reference/simple_stmts.html#augmented-assignment-statements)
+#[violation]
+pub struct UnaryPrefixIncrementDecrement {
+    operator: UnaryPrefixOperatorType,
+}
+
+impl Violation for UnaryPrefixIncrementDecrement {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        let UnaryPrefixIncrementDecrement { operator } = self;
+        match operator {
+            UnaryPrefixOperatorType::Increment => {
+                format!("Python does not support the unary prefix increment operator (`++`)")
+            }
+            UnaryPrefixOperatorType::Decrement => {
+                format!("Python does not support the unary prefix decrement operator (`--`)")
+            }
+        }
+    }
+}
+
+/// B002
+pub(crate) fn unary_prefix_increment_decrement(
+    checker: &mut Checker,
+    expr: &Expr,
+    op: UnaryOp,
+    operand: &Expr,
+) {
+    let Expr::UnaryOp(ast::ExprUnaryOp { op: nested_op, .. }) = operand else {
+        return;
+    };
+    match (op, nested_op) {
+        (UnaryOp::UAdd, UnaryOp::UAdd) => {
+            checker.diagnostics.push(Diagnostic::new(
+                UnaryPrefixIncrementDecrement {
+                    operator: UnaryPrefixOperatorType::Increment,
+                },
+                expr.range(),
+            ));
+        }
+        (UnaryOp::USub, UnaryOp::USub) => {
+            checker.diagnostics.push(Diagnostic::new(
+                UnaryPrefixIncrementDecrement {
+                    operator: UnaryPrefixOperatorType::Decrement,
+                },
+                expr.range(),
+            ));
+        }
+        _ => {}
+    }
+}
+
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+enum UnaryPrefixOperatorType {
+    Increment,
+    Decrement,
+}

crates/ruff/src/rules/flake8_bugbear/snapshots/ruff__rules__flake8_bugbear__tests__B002_B002.py.snap

@@ -1,19 +1,36 @@
 ---
 source: crates/ruff/src/rules/flake8_bugbear/mod.rs
 ---
-B002.py:15:9: B002 Python does not support the unary prefix increment
+B002.py:18:9: B002 Python does not support the unary prefix increment operator (`++`)
    |
-14 | def this_is_buggy(n):
-15 |     x = ++n
+17 | def this_is_buggy(n):
+18 |     x = ++n
    |         ^^^ B002
-16 |     return x
+19 |     y = --n
+20 |     return x, y
    |
 
-B002.py:20:12: B002 Python does not support the unary prefix increment
+B002.py:19:9: B002 Python does not support the unary prefix decrement operator (`--`)
    |
-19 | def this_is_buggy_too(n):
-20 |     return ++n
+17 | def this_is_buggy(n):
+18 |     x = ++n
+19 |     y = --n
+   |         ^^^ B002
+20 |     return x, y
+   |
+
+B002.py:24:12: B002 Python does not support the unary prefix increment operator (`++`)
+   |
+23 | def this_is_buggy_too(n):
+24 |     return ++n, --n
    |            ^^^ B002
    |
 
+B002.py:24:17: B002 Python does not support the unary prefix decrement operator (`--`)
+   |
+23 | def this_is_buggy_too(n):
+24 |     return ++n, --n
+   |                 ^^^ B002
+   |
+