[pylint] Fix PLW0108 autofix introducing a syntax error when the lambda's body contains an assignment expression

crates/ruff_linter/resources/test/fixtures/pylint/unnecessary_lambda.py

@@ -57,3 +57,7 @@
 # lambda uses an additional keyword
 _ = lambda *args: f(*args, y=1)
 _ = lambda *args: f(*args, y=x)
+
+# https://github.com/astral-sh/ruff/issues/18675
+_ = lambda x: (string := str)(x)
+_ = lambda x: ((x := 1) and str)(x)

crates/ruff_linter/src/rules/pylint/rules/unnecessary_lambda.rs

@@ -4,7 +4,7 @@ use ruff_python_ast::{self as ast, Expr, ExprLambda, Parameter, ParameterWithDef
 use ruff_text_size::Ranged;
 
 use crate::checkers::ast::Checker;
-use crate::{AlwaysFixableViolation, Applicability, Edit, Fix};
+use crate::{Applicability, Edit, Fix, FixAvailability, Violation};
 
 /// ## What it does
 /// Checks for `lambda` definitions that consist of a single function call
@@ -46,14 +46,16 @@ use crate::{AlwaysFixableViolation, Applicability, Edit, Fix};
 #[derive(ViolationMetadata)]
 pub(crate) struct UnnecessaryLambda;
 
-impl AlwaysFixableViolation for UnnecessaryLambda {
+impl Violation for UnnecessaryLambda {
+    const FIX_AVAILABILITY: FixAvailability = FixAvailability::Sometimes;
+
     #[derive_message_formats]
     fn message(&self) -> String {
         "Lambda may be unnecessary; consider inlining inner function".to_string()
     }
 
-    fn fix_title(&self) -> String {
-        "Inline function call".to_string()
+    fn fix_title(&self) -> Option<String> {
+        Some("Inline function call".to_string())
     }
 }
 
@@ -199,7 +201,7 @@ pub(crate) fn unnecessary_lambda(checker: &Checker, lambda: &ExprLambda) {
         finder.names
     };
 
-    for name in names {
+    for name in &names {
         if let Some(binding_id) = checker.semantic().resolve_name(name) {
             let binding = checker.semantic().binding(binding_id);
             if checker.semantic().is_current_scope(binding.scope) {
@@ -209,9 +211,32 @@ pub(crate) fn unnecessary_lambda(checker: &Checker, lambda: &ExprLambda) {
     }
 
     let mut diagnostic = checker.report_diagnostic(UnnecessaryLambda, lambda.range());
+    // Suppress the fix if the assignment expression target shadows one of the lambda's parameters.
+    // This is necessary to avoid introducing a change in the behavior of the program.
+    for name in names {
+        if let Some(binding_id) = checker.semantic().lookup_symbol(name.id()) {
+            let binding = checker.semantic().binding(binding_id);
+            if checker
+                .semantic()
+                .current_scope()
+                .shadowed_binding(binding_id)
+                .is_some()
+                && binding
+                    .expression(checker.semantic())
+                    .is_some_and(Expr::is_named_expr)
+            {
+                return;
+            }
+        }
+    }
+
     diagnostic.set_fix(Fix::applicable_edit(
         Edit::range_replacement(
-            checker.locator().slice(func.as_ref()).to_string(),
+            if matches!(func.as_ref(), Expr::Named(_)) {
+                format!("({})", checker.locator().slice(func.as_ref()))
+            } else {
+                checker.locator().slice(func.as_ref()).to_string()
+            },
             lambda.range(),
         ),
         Applicability::Unsafe,

crates/ruff_linter/src/rules/pylint/snapshots/ruff_linter__rules__pylint__tests__PLW0108_unnecessary_lambda.py.snap

@@ -155,3 +155,29 @@ unnecessary_lambda.py:10:5: PLW0108 [*] Lambda may be unnecessary; consider inli
 11 11 | 
 12 12 | # default value in lambda parameters
 13 13 | _ = lambda x=42: print(x)
+
+unnecessary_lambda.py:62:5: PLW0108 [*] Lambda may be unnecessary; consider inlining inner function
+   |
+61 | # https://github.com/astral-sh/ruff/issues/18675
+62 | _ = lambda x: (string := str)(x)
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PLW0108
+63 | _ = lambda x: ((x := 1) and str)(x)
+   |
+   = help: Inline function call
+
+ℹ Unsafe fix
+59 59 | _ = lambda *args: f(*args, y=x)
+60 60 | 
+61 61 | # https://github.com/astral-sh/ruff/issues/18675
+62    |-_ = lambda x: (string := str)(x)
+   62 |+_ = (string := str)
+63 63 | _ = lambda x: ((x := 1) and str)(x)
+
+unnecessary_lambda.py:63:5: PLW0108 Lambda may be unnecessary; consider inlining inner function
+   |
+61 | # https://github.com/astral-sh/ruff/issues/18675
+62 | _ = lambda x: (string := str)(x)
+63 | _ = lambda x: ((x := 1) and str)(x)
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PLW0108
+   |
+   = help: Inline function call