[perflint] Parenthesize generator expressions (PERF401)

crates/ruff_linter/resources/test/fixtures/perflint/PERF401.py

@@ -278,3 +278,15 @@ def f():
     for i in src:
         if lambda: 0:
             dst.append(i)
+
+def f():
+    i = "xyz"
+    result = []
+    for i in range(3):
+        result.append(x for x in [i])
+
+def f():
+    i = "xyz"
+    result = []
+    for i in range(3):
+        result.append((x for x in [i]))

crates/ruff_linter/src/rules/perflint/rules/manual_list_comprehension.rs

@@ -406,7 +406,14 @@ fn convert_to_list_extend(
     };
     let target_str = locator.slice(for_stmt.target.range());
     let elt_str = locator.slice(to_append);
-    let generator_str = format!("{elt_str} {for_type} {target_str} in {for_iter_str}{if_str}");
+    let generator_str = if to_append
+        .as_generator_expr()
+        .is_some_and(|generator| !generator.parenthesized)
+    {
+        format!("({elt_str}) {for_type} {target_str} in {for_iter_str}{if_str}")
+    } else {
+        format!("{elt_str} {for_type} {target_str} in {for_iter_str}{if_str}")
+    };
 
     let variable_name = locator.slice(binding);
     let for_loop_inline_comments = comment_strings_in_range(

crates/ruff_linter/src/rules/perflint/snapshots/ruff_linter__rules__perflint__tests__PERF401_PERF401.py.snap

@@ -241,5 +241,27 @@ PERF401.py:280:13: PERF401 Use `list.extend` to create a transformed list
 279 |         if lambda: 0:
 280 |             dst.append(i)
     |             ^^^^^^^^^^^^^ PERF401
+281 |
+282 | def f():
     |
     = help: Replace for loop with list.extend
+
+PERF401.py:286:9: PERF401 Use a list comprehension to create a transformed list
+    |
+284 |     result = []
+285 |     for i in range(3):
+286 |         result.append(x for x in [i])
+    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PERF401
+287 |
+288 | def f():
+    |
+    = help: Replace for loop with list comprehension
+
+PERF401.py:292:9: PERF401 Use a list comprehension to create a transformed list
+    |
+290 |     result = []
+291 |     for i in range(3):
+292 |         result.append((x for x in [i]))
+    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PERF401
+    |
+    = help: Replace for loop with list comprehension

crates/ruff_linter/src/rules/perflint/snapshots/ruff_linter__rules__perflint__tests__preview__PERF401_PERF401.py.snap

@@ -566,6 +566,8 @@ PERF401.py:280:13: PERF401 [*] Use `list.extend` to create a transformed list
 279 |         if lambda: 0:
 280 |             dst.append(i)
     |             ^^^^^^^^^^^^^ PERF401
+281 |
+282 | def f():
     |
     = help: Replace for loop with list.extend
 
@@ -577,3 +579,47 @@ PERF401.py:280:13: PERF401 [*] Use `list.extend` to create a transformed list
 279     |-        if lambda: 0:
 280     |-            dst.append(i)
     278 |+    dst.extend(i for i in src if (lambda: 0))
+281 279 | 
+282 280 | def f():
+283 281 |     i = "xyz"
+
+PERF401.py:286:9: PERF401 [*] Use a list comprehension to create a transformed list
+    |
+284 |     result = []
+285 |     for i in range(3):
+286 |         result.append(x for x in [i])
+    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PERF401
+287 |
+288 | def f():
+    |
+    = help: Replace for loop with list comprehension
+
+ℹ Unsafe fix
+281 281 | 
+282 282 | def f():
+283 283 |     i = "xyz"
+284     |-    result = []
+285     |-    for i in range(3):
+286     |-        result.append(x for x in [i])
+    284 |+    result = [(x for x in [i]) for i in range(3)]
+287 285 | 
+288 286 | def f():
+289 287 |     i = "xyz"
+
+PERF401.py:292:9: PERF401 [*] Use a list comprehension to create a transformed list
+    |
+290 |     result = []
+291 |     for i in range(3):
+292 |         result.append((x for x in [i]))
+    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PERF401
+    |
+    = help: Replace for loop with list comprehension
+
+ℹ Unsafe fix
+287 287 | 
+288 288 | def f():
+289 289 |     i = "xyz"
+290     |-    result = []
+291     |-    for i in range(3):
+292     |-        result.append((x for x in [i]))
+    290 |+    result = [(x for x in [i]) for i in range(3)]