[flake8_bugbear] message based on expression location [B015]

crates/ruff_linter/resources/test/fixtures/flake8_bugbear/B015.py

@@ -17,6 +17,11 @@ def test():
     1 in (1, 2)
 
 
+def test2():
+    1 in (1, 2)
+    return
+
+
 data = [x for x in [1, 2, 3] if x in (1, 2)]
 
 

crates/ruff_linter/src/rules/flake8_bugbear/rules/useless_comparison.rs

@@ -1,6 +1,7 @@
 use ruff_diagnostics::{Diagnostic, Violation};
 use ruff_macros::{derive_message_formats, violation};
-use ruff_python_ast::Expr;
+use ruff_python_ast::{Expr, Stmt};
+use ruff_python_semantic::ScopeKind;
 use ruff_text_size::Ranged;
 
 use crate::checkers::ast::Checker;
@@ -33,33 +34,69 @@ use super::super::helpers::at_last_top_level_expression_in_cell;
 /// ## References
 /// - [Python documentation: `assert` statement](https://docs.python.org/3/reference/simple_stmts.html#the-assert-statement)
 #[violation]
-pub struct UselessComparison;
+pub struct UselessComparison {
+    at: ComparisonLocationAt,
+}
 
 impl Violation for UselessComparison {
     #[derive_message_formats]
     fn message(&self) -> String {
-        format!(
-            "Pointless comparison. Did you mean to assign a value? \
-             Otherwise, prepend `assert` or remove it."
-        )
+        match self.at {
+            ComparisonLocationAt::MiddleBody => format!(
+                "Pointless comparison. Did you mean to assign a value? \
+                Otherwise, prepend `assert` or remove it."
+            ),
+            ComparisonLocationAt::EndOfFunction => format!(
+                "Pointless comparison at end of function scope. Did you mean \
+                to return the expression result?"
+            ),
+        }
     }
 }
 
 /// B015
 pub(crate) fn useless_comparison(checker: &mut Checker, expr: &Expr) {
     if expr.is_compare_expr() {
+        let semantic = checker.semantic();
+
         if checker.source_type.is_ipynb()
             && at_last_top_level_expression_in_cell(
-                checker.semantic(),
+                semantic,
                 checker.locator(),
                 checker.cell_offsets(),
             )
         {
             return;
         }
 
-        checker
-            .diagnostics
-            .push(Diagnostic::new(UselessComparison, expr.range()));
+        if let ScopeKind::Function(func_def) = semantic.current_scope().kind {
+            if func_def
+                .body
+                .last()
+                .and_then(Stmt::as_expr_stmt)
+                .is_some_and(|last_stmt| &*last_stmt.value == expr)
+            {
+                checker.diagnostics.push(Diagnostic::new(
+                    UselessComparison {
+                        at: ComparisonLocationAt::EndOfFunction,
+                    },
+                    expr.range(),
+                ));
+                return;
+            }
+        }
+
+        checker.diagnostics.push(Diagnostic::new(
+            UselessComparison {
+                at: ComparisonLocationAt::MiddleBody,
+            },
+            expr.range(),
+        ));
     }
 }
+
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+enum ComparisonLocationAt {
+    MiddleBody,
+    EndOfFunction,
+}

crates/ruff_linter/src/rules/flake8_bugbear/snapshots/ruff_linter__rules__flake8_bugbear__tests__B015_B015.py.snap

@@ -1,5 +1,6 @@
 ---
 source: crates/ruff_linter/src/rules/flake8_bugbear/mod.rs
+assertion_line: 74
 ---
 B015.py:3:1: B015 Pointless comparison. Did you mean to assign a value? Otherwise, prepend `assert` or remove it.
   |
@@ -19,19 +20,25 @@ B015.py:7:1: B015 Pointless comparison. Did you mean to assign a value? Otherwis
   | ^^^^^^^^^^^ B015
   |
 
-B015.py:17:5: B015 Pointless comparison. Did you mean to assign a value? Otherwise, prepend `assert` or remove it.
+B015.py:17:5: B015 Pointless comparison at end of function scope. Did you mean to return the expression result?
    |
 15 |     assert 1 in (1, 2)
 16 | 
 17 |     1 in (1, 2)
    |     ^^^^^^^^^^^ B015
    |
 
-B015.py:24:5: B015 Pointless comparison. Did you mean to assign a value? Otherwise, prepend `assert` or remove it.
+B015.py:21:5: B015 Pointless comparison. Did you mean to assign a value? Otherwise, prepend `assert` or remove it.
    |
-23 | class TestClass:
-24 |     1 == 1
-   |     ^^^^^^ B015
+20 | def test2():
+21 |     1 in (1, 2)
+   |     ^^^^^^^^^^^ B015
+22 |     return
    |
 
-
+B015.py:29:5: B015 Pointless comparison. Did you mean to assign a value? Otherwise, prepend `assert` or remove it.
+   |
+28 | class TestClass:
+29 |     1 == 1
+   |     ^^^^^^ B015
+   |