Improvements to RUF015

crates/ruff_linter/resources/test/fixtures/ruff/RUF015.py

@@ -38,10 +38,26 @@
 list(range(10))[0]
 list(x.y)[0]
 list(x["y"])[0]
+[*range(10)][0]
+[*x["y"]][0]
+[*x.y][0]
+[* x.y][0]
+[
+    *x.y
+][0]
 
 # RUF015 (multi-line)
 revision_heads_map_ast = [
     a
     for a in revision_heads_map_ast_obj.body
     if isinstance(a, ast.Assign) and a.targets[0].id == "REVISION_HEADS_MAP"
 ][0]
+
+# RUF015 (zip)
+list(zip(x, y))[0]
+[*zip(x, y)][0]
+
+
+def test():
+    zip = list  # Overwrite the builtin zip
+    list(zip(x, y))[0]

crates/ruff_linter/src/rules/ruff/rules/unnecessary_iterable_allocation_for_first_element.rs

@@ -4,6 +4,7 @@ use ruff_diagnostics::{AlwaysFixableViolation, Diagnostic, Edit, Fix};
 use ruff_macros::{derive_message_formats, violation};
 use ruff_python_ast::{self as ast, Arguments, Comprehension, Constant, Expr, Int};
 use ruff_python_semantic::SemanticModel;
+use ruff_python_stdlib::builtins::is_iterator;
 use ruff_text_size::{Ranged, TextRange, TextSize};
 
 use crate::checkers::ast::Checker;
@@ -185,6 +186,10 @@ fn match_iteration_target(expr: &Expr, semantic: &SemanticModel) -> Option<Itera
                         iterable: true,
                     },
                 },
+                Expr::Call(ast::ExprCall { func, .. }) => IterationTarget {
+                    range: arg.range(),
+                    iterable: is_func_builtin_iterator(func, semantic),
+                },
                 _ => IterationTarget {
                     range: arg.range(),
                     iterable: false,
@@ -209,7 +214,24 @@ fn match_iteration_target(expr: &Expr, semantic: &SemanticModel) -> Option<Itera
                 iterable: true,
             },
         },
+        Expr::List(ast::ExprList { elts, .. }) => {
+            let [elt] = elts.as_slice() else {
+                return None;
+            };
+            let Expr::Starred(ast::ExprStarred { value, .. }) = elt else {
+                return None;
+            };
 
+            let iterable = if value.is_call_expr() {
+                is_func_builtin_iterator(&value.as_call_expr()?.func, semantic)
+            } else {
+                false
+            };
+            IterationTarget {
+                range: value.range(),
+                iterable,
+            }
+        }
         _ => return None,
     };
 
@@ -240,3 +262,10 @@ fn match_simple_comprehension(elt: &Expr, generators: &[Comprehension]) -> Optio
 
     Some(generator.iter.range())
 }
+
+/// Returns `true` if the function is a builtin iterator.
+fn is_func_builtin_iterator(func: &Expr, semantic: &SemanticModel) -> bool {
+    func.as_name_expr().map_or(false, |func_name| {
+        is_iterator(func_name.id.as_str()) && semantic.is_builtin(func_name.id.as_str())
+    })
+}

crates/ruff_linter/src/rules/ruff/snapshots/ruff_linter__rules__ruff__tests__RUF015_RUF015.py.snap

@@ -183,7 +183,7 @@ RUF015.py:38:1: RUF015 [*] Prefer `next(iter(range(10)))` over single element sl
    38 |+next(iter(range(10)))
 39 39 | list(x.y)[0]
 40 40 | list(x["y"])[0]
-41 41 | 
+41 41 | [*range(10)][0]
 
 RUF015.py:39:1: RUF015 [*] Prefer `next(iter(x.y))` over single element slice
    |
@@ -192,6 +192,7 @@ RUF015.py:39:1: RUF015 [*] Prefer `next(iter(x.y))` over single element slice
 39 | list(x.y)[0]
    | ^^^^^^^^^^^^ RUF015
 40 | list(x["y"])[0]
+41 | [*range(10)][0]
    |
    = help: Replace with `next(iter(x.y))`
 
@@ -202,17 +203,17 @@ RUF015.py:39:1: RUF015 [*] Prefer `next(iter(x.y))` over single element slice
 39    |-list(x.y)[0]
    39 |+next(iter(x.y))
 40 40 | list(x["y"])[0]
-41 41 | 
-42 42 | # RUF015 (multi-line)
+41 41 | [*range(10)][0]
+42 42 | [*x["y"]][0]
 
 RUF015.py:40:1: RUF015 [*] Prefer `next(iter(x["y"]))` over single element slice
    |
 38 | list(range(10))[0]
 39 | list(x.y)[0]
 40 | list(x["y"])[0]
    | ^^^^^^^^^^^^^^^ RUF015
-41 | 
-42 | # RUF015 (multi-line)
+41 | [*range(10)][0]
+42 | [*x["y"]][0]
    |
    = help: Replace with `next(iter(x["y"]))`
 
@@ -222,33 +223,201 @@ RUF015.py:40:1: RUF015 [*] Prefer `next(iter(x["y"]))` over single element slice
 39 39 | list(x.y)[0]
 40    |-list(x["y"])[0]
    40 |+next(iter(x["y"]))
-41 41 | 
-42 42 | # RUF015 (multi-line)
-43 43 | revision_heads_map_ast = [
+41 41 | [*range(10)][0]
+42 42 | [*x["y"]][0]
+43 43 | [*x.y][0]
 
-RUF015.py:43:26: RUF015 [*] Prefer `next(...)` over single element slice
+RUF015.py:41:1: RUF015 [*] Prefer `next(iter(range(10)))` over single element slice
    |
-42 |   # RUF015 (multi-line)
-43 |   revision_heads_map_ast = [
-   |  __________________________^
-44 | |     a
-45 | |     for a in revision_heads_map_ast_obj.body
-46 | |     if isinstance(a, ast.Assign) and a.targets[0].id == "REVISION_HEADS_MAP"
+39 | list(x.y)[0]
+40 | list(x["y"])[0]
+41 | [*range(10)][0]
+   | ^^^^^^^^^^^^^^^ RUF015
+42 | [*x["y"]][0]
+43 | [*x.y][0]
+   |
+   = help: Replace with `next(iter(range(10)))`
+
+ℹ Suggested fix
+38 38 | list(range(10))[0]
+39 39 | list(x.y)[0]
+40 40 | list(x["y"])[0]
+41    |-[*range(10)][0]
+   41 |+next(iter(range(10)))
+42 42 | [*x["y"]][0]
+43 43 | [*x.y][0]
+44 44 | [* x.y][0]
+
+RUF015.py:42:1: RUF015 [*] Prefer `next(iter(x["y"]))` over single element slice
+   |
+40 | list(x["y"])[0]
+41 | [*range(10)][0]
+42 | [*x["y"]][0]
+   | ^^^^^^^^^^^^ RUF015
+43 | [*x.y][0]
+44 | [* x.y][0]
+   |
+   = help: Replace with `next(iter(x["y"]))`
+
+ℹ Suggested fix
+39 39 | list(x.y)[0]
+40 40 | list(x["y"])[0]
+41 41 | [*range(10)][0]
+42    |-[*x["y"]][0]
+   42 |+next(iter(x["y"]))
+43 43 | [*x.y][0]
+44 44 | [* x.y][0]
+45 45 | [
+
+RUF015.py:43:1: RUF015 [*] Prefer `next(iter(x.y))` over single element slice
+   |
+41 | [*range(10)][0]
+42 | [*x["y"]][0]
+43 | [*x.y][0]
+   | ^^^^^^^^^ RUF015
+44 | [* x.y][0]
+45 | [
+   |
+   = help: Replace with `next(iter(x.y))`
+
+ℹ Suggested fix
+40 40 | list(x["y"])[0]
+41 41 | [*range(10)][0]
+42 42 | [*x["y"]][0]
+43    |-[*x.y][0]
+   43 |+next(iter(x.y))
+44 44 | [* x.y][0]
+45 45 | [
+46 46 |     *x.y
+
+RUF015.py:44:1: RUF015 [*] Prefer `next(iter(x.y))` over single element slice
+   |
+42 | [*x["y"]][0]
+43 | [*x.y][0]
+44 | [* x.y][0]
+   | ^^^^^^^^^^ RUF015
+45 | [
+46 |     *x.y
+   |
+   = help: Replace with `next(iter(x.y))`
+
+ℹ Suggested fix
+41 41 | [*range(10)][0]
+42 42 | [*x["y"]][0]
+43 43 | [*x.y][0]
+44    |-[* x.y][0]
+   44 |+next(iter(x.y))
+45 45 | [
+46 46 |     *x.y
+47 47 | ][0]
+
+RUF015.py:45:1: RUF015 [*] Prefer `next(iter(x.y))` over single element slice
+   |
+43 |   [*x.y][0]
+44 |   [* x.y][0]
+45 | / [
+46 | |     *x.y
 47 | | ][0]
    | |____^ RUF015
+48 |   
+49 |   # RUF015 (multi-line)
    |
-   = help: Replace with `next(...)`
+   = help: Replace with `next(iter(x.y))`
 
 ℹ Suggested fix
-40 40 | list(x["y"])[0]
-41 41 | 
-42 42 | # RUF015 (multi-line)
-43    |-revision_heads_map_ast = [
-   43 |+revision_heads_map_ast = next(
-44 44 |     a
-45 45 |     for a in revision_heads_map_ast_obj.body
-46 46 |     if isinstance(a, ast.Assign) and a.targets[0].id == "REVISION_HEADS_MAP"
+42 42 | [*x["y"]][0]
+43 43 | [*x.y][0]
+44 44 | [* x.y][0]
+45    |-[
+46    |-    *x.y
 47    |-][0]
-   47 |+)
+   45 |+next(iter(x.y))
+48 46 | 
+49 47 | # RUF015 (multi-line)
+50 48 | revision_heads_map_ast = [
+
+RUF015.py:50:26: RUF015 [*] Prefer `next(...)` over single element slice
+   |
+49 |   # RUF015 (multi-line)
+50 |   revision_heads_map_ast = [
+   |  __________________________^
+51 | |     a
+52 | |     for a in revision_heads_map_ast_obj.body
+53 | |     if isinstance(a, ast.Assign) and a.targets[0].id == "REVISION_HEADS_MAP"
+54 | | ][0]
+   | |____^ RUF015
+55 |   
+56 |   # RUF015 (zip)
+   |
+   = help: Replace with `next(...)`
+
+ℹ Suggested fix
+47 47 | ][0]
+48 48 | 
+49 49 | # RUF015 (multi-line)
+50    |-revision_heads_map_ast = [
+   50 |+revision_heads_map_ast = next(
+51 51 |     a
+52 52 |     for a in revision_heads_map_ast_obj.body
+53 53 |     if isinstance(a, ast.Assign) and a.targets[0].id == "REVISION_HEADS_MAP"
+54    |-][0]
+   54 |+)
+55 55 | 
+56 56 | # RUF015 (zip)
+57 57 | list(zip(x, y))[0]
+
+RUF015.py:57:1: RUF015 [*] Prefer `next(zip(x, y))` over single element slice
+   |
+56 | # RUF015 (zip)
+57 | list(zip(x, y))[0]
+   | ^^^^^^^^^^^^^^^^^^ RUF015
+58 | [*zip(x, y)][0]
+   |
+   = help: Replace with `next(zip(x, y))`
+
+ℹ Suggested fix
+54 54 | ][0]
+55 55 | 
+56 56 | # RUF015 (zip)
+57    |-list(zip(x, y))[0]
+   57 |+next(zip(x, y))
+58 58 | [*zip(x, y)][0]
+59 59 | 
+60 60 | 
+
+RUF015.py:58:1: RUF015 [*] Prefer `next(zip(x, y))` over single element slice
+   |
+56 | # RUF015 (zip)
+57 | list(zip(x, y))[0]
+58 | [*zip(x, y)][0]
+   | ^^^^^^^^^^^^^^^ RUF015
+   |
+   = help: Replace with `next(zip(x, y))`
+
+ℹ Suggested fix
+55 55 | 
+56 56 | # RUF015 (zip)
+57 57 | list(zip(x, y))[0]
+58    |-[*zip(x, y)][0]
+   58 |+next(zip(x, y))
+59 59 | 
+60 60 | 
+61 61 | def test():
+
+RUF015.py:63:5: RUF015 [*] Prefer `next(iter(zip(x, y)))` over single element slice
+   |
+61 | def test():
+62 |     zip = list  # Overwrite the builtin zip
+63 |     list(zip(x, y))[0]
+   |     ^^^^^^^^^^^^^^^^^^ RUF015
+   |
+   = help: Replace with `next(iter(zip(x, y)))`
+
+ℹ Suggested fix
+60 60 | 
+61 61 | def test():
+62 62 |     zip = list  # Overwrite the builtin zip
+63    |-    list(zip(x, y))[0]
+   63 |+    next(iter(zip(x, y)))
 
 

crates/ruff_python_stdlib/src/builtins.rs

@@ -337,3 +337,11 @@ pub fn is_builtin(name: &str) -> bool {
             | "zip"
     )
 }
+
+/// Returns `true` if the given name is that of a Python builtin iterator.
+pub fn is_iterator(name: &str) -> bool {
+    matches!(
+        name,
+        "enumerate" | "filter" | "map" | "reversed" | "zip" | "iter"
+    )
+}