[flake8-simplify] Apply SIM113 when index variable is of type int

crates/ruff_linter/resources/test/fixtures/flake8_simplify/SIM113.py

@@ -46,7 +46,8 @@ def func():
 
 
 def func():
-    # OK (index doesn't start at 0
+    # SIM113
+    # https://github.com/astral-sh/ruff/pull/21395
     idx = 10
     for x in range(5):
         g(x, idx)

crates/ruff_linter/src/preview.rs

@@ -269,3 +269,8 @@ pub(crate) const fn is_typing_extensions_str_alias_enabled(settings: &LinterSett
 pub(crate) const fn is_extended_i18n_function_matching_enabled(settings: &LinterSettings) -> bool {
     settings.preview.is_enabled()
 }
+
+// https://github.com/astral-sh/ruff/pull/21395
+pub(crate) const fn is_enumerate_for_loop_int_index_enabled(settings: &LinterSettings) -> bool {
+    settings.preview.is_enabled()
+}

crates/ruff_linter/src/rules/flake8_simplify/mod.rs

@@ -61,6 +61,7 @@ mod tests {
 
     #[test_case(Rule::SplitStaticString, Path::new("SIM905.py"))]
     #[test_case(Rule::DictGetWithNoneDefault, Path::new("SIM910.py"))]
+    #[test_case(Rule::EnumerateForLoop, Path::new("SIM113.py"))]
     fn preview_rules(rule_code: Rule, path: &Path) -> Result<()> {
         let snapshot = format!(
             "preview__{}_{}",

crates/ruff_linter/src/rules/flake8_simplify/rules/enumerate_for_loop.rs

@@ -1,6 +1,8 @@
+use crate::preview::is_enumerate_for_loop_int_index_enabled;
 use ruff_macros::{ViolationMetadata, derive_message_formats};
 use ruff_python_ast::statement_visitor::{StatementVisitor, walk_stmt};
 use ruff_python_ast::{self as ast, Expr, Int, Number, Operator, Stmt};
+use ruff_python_semantic::analyze::type_inference::{NumberLike, PythonType, ResolvedPythonType};
 use ruff_python_semantic::analyze::typing;
 use ruff_text_size::Ranged;
 
@@ -11,6 +13,9 @@ use crate::checkers::ast::Checker;
 /// Checks for `for` loops with explicit loop-index variables that can be replaced
 /// with `enumerate()`.
 ///
+/// In [preview], this rule checks for index variables initialized with any integer rather than only
+/// a literal zero.
+///
 /// ## Why is this bad?
 /// When iterating over a sequence, it's often desirable to keep track of the
 /// index of each element alongside the element itself. Prefer the `enumerate`
@@ -35,6 +40,8 @@ use crate::checkers::ast::Checker;
 ///
 /// ## References
 /// - [Python documentation: `enumerate`](https://docs.python.org/3/library/functions.html#enumerate)
+///
+/// [preview]: https://docs.astral.sh/ruff/preview/
 #[derive(ViolationMetadata)]
 #[violation_metadata(stable_since = "v0.2.0")]
 pub(crate) struct EnumerateForLoop {
@@ -82,17 +89,21 @@ pub(crate) fn enumerate_for_loop(checker: &Checker, for_stmt: &ast::StmtFor) {
                 continue;
             }
 
-            // Ensure that the index variable was initialized to 0.
+            // Ensure that the index variable was initialized to 0 (or instance of `int` if preview is enabled).
             let Some(value) = typing::find_binding_value(binding, checker.semantic()) else {
                 continue;
             };
-            if !matches!(
+            if !(matches!(
                 value,
                 Expr::NumberLiteral(ast::ExprNumberLiteral {
                     value: Number::Int(Int::ZERO),
                     ..
                 })
-            ) {
+            ) || matches!(
+                ResolvedPythonType::from(value),
+                ResolvedPythonType::Atom(PythonType::Number(NumberLike::Integer))
+            ) && is_enumerate_for_loop_int_index_enabled(checker.settings()))
+            {
                 continue;
             }
 

crates/ruff_linter/src/rules/flake8_simplify/snapshots/ruff_linter__rules__flake8_simplify__tests__preview__SIM113_SIM113.py.snap

@@ -0,0 +1,60 @@
+---
+source: crates/ruff_linter/src/rules/flake8_simplify/mod.rs
+---
+SIM113 Use `enumerate()` for index variable `idx` in `for` loop
+ --> SIM113.py:6:9
+  |
+4 |     for x in range(5):
+5 |         g(x, idx)
+6 |         idx += 1
+  |         ^^^^^^^^
+7 |         h(x)
+  |
+
+SIM113 Use `enumerate()` for index variable `idx` in `for` loop
+  --> SIM113.py:17:9
+   |
+15 |         if g(x):
+16 |             break
+17 |         idx += 1
+   |         ^^^^^^^^
+18 |         sum += h(x, idx)
+   |
+
+SIM113 Use `enumerate()` for index variable `idx` in `for` loop
+  --> SIM113.py:27:9
+   |
+25 |         g(x)
+26 |         h(x, y)
+27 |         idx += 1
+   |         ^^^^^^^^
+   |
+
+SIM113 Use `enumerate()` for index variable `idx` in `for` loop
+  --> SIM113.py:36:9
+   |
+34 |     for x in range(5):
+35 |         sum += h(x, idx)
+36 |         idx += 1
+   |         ^^^^^^^^
+   |
+
+SIM113 Use `enumerate()` for index variable `idx` in `for` loop
+  --> SIM113.py:44:9
+   |
+42 |     for x in range(5):
+43 |         g(x, idx)
+44 |         idx += 1
+   |         ^^^^^^^^
+45 |         h(x)
+   |
+
+SIM113 Use `enumerate()` for index variable `idx` in `for` loop
+  --> SIM113.py:54:9
+   |
+52 |     for x in range(5):
+53 |         g(x, idx)
+54 |         idx += 1
+   |         ^^^^^^^^
+55 |         h(x)
+   |