[pylint] - add unnecessary-list-index-lookup (PLR1736) + autofix

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

@@ -0,0 +1,59 @@
+import builtins
+
+letters = ["a", "b", "c"]
+
+
+def fix_these():
+    [letters[index] for index, letter in enumerate(letters)]  # PLR1736
+    {letters[index] for index, letter in enumerate(letters)}  # PLR1736
+    {letter: letters[index] for index, letter in enumerate(letters)}  # PLR1736
+
+    for index, letter in enumerate(letters):
+        print(letters[index])  # PLR1736
+        blah = letters[index]  # PLR1736
+        assert letters[index]  == "d"  # PLR1736
+
+    for index, letter in builtins.enumerate(letters):
+        print(letters[index])  # PLR1736
+        blah = letters[index]  # PLR1736
+        assert letters[index]  == "d"  # PLR1736
+
+
+def dont_fix_these():
+    # once there is an assignment to the sequence[index], we stop emitting diagnostics
+    for index, letter in enumerate(letters):
+        letters[index] = "d"  # Ok
+        letters[index] += "e"  # Ok
+        assert letters[index] == "de"  # Ok
+
+    # once there is an assignment to the index, we stop emitting diagnostics
+    for index, letter in enumerate(letters):
+        index += 1  # Ok
+        print(letters[index])  # Ok
+
+    # once there is an assignment to the sequence, we stop emitting diagnostics
+    for index, letter in enumerate(letters):
+        letters = ["d", "e", "f"]  # Ok
+        print(letters[index])  # Ok
+
+    # once there is an deletion from or of the sequence or index, we stop emitting diagnostics
+    for index, letter in enumerate(letters):
+        del letters[index]  # Ok
+        print(letters[index])  # Ok
+    for index, letter in enumerate(letters):
+        del letters  # Ok
+        print(letters[index])  # Ok
+    for index, letter in enumerate(letters):
+        del index  # Ok
+        print(letters[index])  # Ok
+
+
+def value_intentionally_unused():
+    [letters[index] for index, _ in enumerate(letters)]  # Ok
+    {letters[index] for index, _ in enumerate(letters)}  # Ok
+    {index: letters[index] for index, _ in enumerate(letters)}  # Ok
+
+    for index, _ in enumerate(letters):
+        print(letters[index])  # Ok
+        blah = letters[index]  # Ok
+        letters[index] = "d"  # Ok

crates/ruff_linter/src/checkers/ast/analyze/expression.rs

@@ -1317,6 +1317,9 @@ pub(crate) fn expression(expr: &Expr, checker: &mut Checker) {
                 range: _,
             },
         ) => {
+            if checker.enabled(Rule::UnnecessaryListIndexLookup) {
+                pylint::rules::unnecessary_list_index_lookup_comprehension(checker, expr);
+            }
             if checker.enabled(Rule::UnnecessaryComprehension) {
                 flake8_comprehensions::rules::unnecessary_list_set_comprehension(
                     checker, expr, elt, generators,
@@ -1341,6 +1344,9 @@ pub(crate) fn expression(expr: &Expr, checker: &mut Checker) {
                 range: _,
             },
         ) => {
+            if checker.enabled(Rule::UnnecessaryListIndexLookup) {
+                pylint::rules::unnecessary_list_index_lookup_comprehension(checker, expr);
+            }
             if checker.enabled(Rule::UnnecessaryComprehension) {
                 flake8_comprehensions::rules::unnecessary_list_set_comprehension(
                     checker, expr, elt, generators,
@@ -1364,6 +1370,9 @@ pub(crate) fn expression(expr: &Expr, checker: &mut Checker) {
             generators,
             range: _,
         }) => {
+            if checker.enabled(Rule::UnnecessaryListIndexLookup) {
+                pylint::rules::unnecessary_list_index_lookup_comprehension(checker, expr);
+            }
             if checker.enabled(Rule::UnnecessaryComprehension) {
                 flake8_comprehensions::rules::unnecessary_dict_comprehension(
                     checker, expr, key, value, generators,
@@ -1388,6 +1397,9 @@ pub(crate) fn expression(expr: &Expr, checker: &mut Checker) {
                 range: _,
             },
         ) => {
+            if checker.enabled(Rule::UnnecessaryListIndexLookup) {
+                pylint::rules::unnecessary_list_index_lookup_comprehension(checker, expr);
+            }
             if checker.enabled(Rule::FunctionUsesLoopVariable) {
                 flake8_bugbear::rules::function_uses_loop_variable(checker, &Node::Expr(expr));
             }

crates/ruff_linter/src/checkers/ast/analyze/statement.rs

@@ -1271,6 +1271,9 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
             if checker.enabled(Rule::UnnecessaryListCast) {
                 perflint::rules::unnecessary_list_cast(checker, iter, body);
             }
+            if checker.enabled(Rule::UnnecessaryListIndexLookup) {
+                pylint::rules::unnecessary_list_index_lookup(checker, for_stmt);
+            }
             if !is_async {
                 if checker.enabled(Rule::ReimplementedBuiltin) {
                     flake8_simplify::rules::convert_for_loop_to_any_all(checker, stmt);

crates/ruff_linter/src/codes.rs

@@ -258,6 +258,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Pylint, "R1714") => (RuleGroup::Stable, rules::pylint::rules::RepeatedEqualityComparison),
         (Pylint, "R1706") => (RuleGroup::Preview, rules::pylint::rules::AndOrTernary),
         (Pylint, "R1722") => (RuleGroup::Stable, rules::pylint::rules::SysExitAlias),
+        (Pylint, "R1736") => (RuleGroup::Preview, rules::pylint::rules::UnnecessaryListIndexLookup),
         (Pylint, "R2004") => (RuleGroup::Stable, rules::pylint::rules::MagicValueComparison),
         (Pylint, "R5501") => (RuleGroup::Stable, rules::pylint::rules::CollapsibleElseIf),
         (Pylint, "R6201") => (RuleGroup::Preview, rules::pylint::rules::LiteralMembership),

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

@@ -154,6 +154,10 @@ mod tests {
         Rule::RepeatedKeywordArgument,
         Path::new("repeated_keyword_argument.py")
     )]
+    #[test_case(
+        Rule::UnnecessaryListIndexLookup,
+        Path::new("unnecessary_list_index_lookup.py")
+    )]
     fn rules(rule_code: Rule, path: &Path) -> Result<()> {
         let snapshot = format!("{}_{}", rule_code.noqa_code(), path.to_string_lossy());
         let diagnostics = test_path(

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

@@ -63,6 +63,7 @@ pub(crate) use type_param_name_mismatch::*;
 pub(crate) use unexpected_special_method_signature::*;
 pub(crate) use unnecessary_direct_lambda_call::*;
 pub(crate) use unnecessary_lambda::*;
+pub(crate) use unnecessary_list_index_lookup::*;
 pub(crate) use unspecified_encoding::*;
 pub(crate) use useless_else_on_loop::*;
 pub(crate) use useless_import_alias::*;
@@ -136,6 +137,7 @@ mod type_param_name_mismatch;
 mod unexpected_special_method_signature;
 mod unnecessary_direct_lambda_call;
 mod unnecessary_lambda;
+mod unnecessary_list_index_lookup;
 mod unspecified_encoding;
 mod useless_else_on_loop;
 mod useless_import_alias;