Refine some `perflint` rules (#5484)

## Summary

Removing some false positives based on running over `zulip`.

`PERF401` now also detects cases like:

```py
original = list(range(10000))
filtered = []
for i in original:
    filtered.append(i * i)
```

Previously, these were caught by the list-copy rule, but these too need
comprehensions.

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

@@ -1,4 +1,4 @@
-def foo():
+def f():
     items = [1, 2, 3, 4]
     result = []
     for i in items:
@@ -6,8 +6,15 @@ def foo():
             result.append(i)  # PERF401
 
 
-def foo():
+def f():
-    items = [1,2,3,4]
+    items = [1, 2, 3, 4]
+    result = []
+    for i in items:
+        result.append(i * i)  # PERF401
+
+
+def f():
+    items = [1, 2, 3, 4]
     result = []
     for i in items:
         if i % 2:
@@ -16,3 +23,10 @@ def foo():
             result.append(i)  # PERF401
         else:
             result.append(i)  # PERF401
+
+
+def f():
+    items = [1, 2, 3, 4]
+    result = []
+    for i in items:
+        result.append(i)  # OK

crates/ruff/resources/test/fixtures/perflint/PERF402.py

@@ -1,12 +1,19 @@
-def foo():
+def f():
     items = [1, 2, 3, 4]
     result = []
     for i in items:
         result.append(i)  # PERF402
 
 
-def foo():
+def f():
     items = [1, 2, 3, 4]
     result = []
     for i in items:
         result.insert(0, i)  # PERF402
+
+
+def f():
+    items = [1, 2, 3, 4]
+    result = []
+    for i in items:
+        result.append(i * i)  # OK

crates/ruff/src/checkers/ast/mod.rs

@@ -1525,10 +1525,10 @@ where
                     perflint::rules::incorrect_dict_iterator(self, target, iter);
                 }
                 if self.enabled(Rule::ManualListComprehension) {
-                    perflint::rules::manual_list_comprehension(self, body);
+                    perflint::rules::manual_list_comprehension(self, target, body);
                 }
                 if self.enabled(Rule::ManualListCopy) {
-                    perflint::rules::manual_list_copy(self, body);
+                    perflint::rules::manual_list_copy(self, target, body);
                 }
                 if self.enabled(Rule::UnnecessaryListCast) {
                     perflint::rules::unnecessary_list_cast(self, iter);

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

@@ -9,7 +9,7 @@ use crate::checkers::ast::Checker;
 /// Checks for `for` loops that can be replaced by a list comprehension.
 ///
 /// ## Why is this bad?
-/// When creating a filtered list from an existing list using a for-loop,
+/// When creating a transformed list from an existing list using a for-loop,
 /// prefer a list comprehension. List comprehensions are more readable and
 /// more performant.
 ///
@@ -34,43 +34,87 @@ use crate::checkers::ast::Checker;
 /// original = list(range(10000))
 /// filtered = [x for x in original if x % 2]
 /// ```
+///
+/// If you're appending to an existing list, use the `extend` method instead:
+/// ```python
+/// original = list(range(10000))
+/// filtered.extend(x for x in original if x % 2)
+/// ```
 #[violation]
 pub struct ManualListComprehension;
 
 impl Violation for ManualListComprehension {
     #[derive_message_formats]
     fn message(&self) -> String {
-        format!("Use a list comprehension to create a new filtered list")
+        format!("Use a list comprehension to create a transformed list")
     }
 }
 
 /// PERF401
-pub(crate) fn manual_list_comprehension(checker: &mut Checker, body: &[Stmt]) {
+pub(crate) fn manual_list_comprehension(checker: &mut Checker, target: &Expr, body: &[Stmt]) {
-    let [stmt] = body else {
+    let (stmt, conditional) = match body {
+        // ```python
+        // for x in y:
+        //     if z:
+        //         filtered.append(x)
+        // ```
+        [Stmt::If(ast::StmtIf { body, orelse, .. })] => {
+            if !orelse.is_empty() {
+                return;
+            }
+            let [stmt] = body.as_slice() else {
+                return;
+            };
+            (stmt, true)
+        }
+        // ```python
+        // for x in y:
+        //     filtered.append(f(x))
+        // ```
+        [stmt] => (stmt, false),
+        _ => return,
+    };
+
+    let Stmt::Expr(ast::StmtExpr { value, .. }) = stmt else {
         return;
     };
 
-    let Stmt::If(ast::StmtIf { body, .. }) = stmt else {
+    let Expr::Call(ast::ExprCall {
+        func,
+        range,
+        args,
+        keywords,
+    }) = value.as_ref()
+    else {
         return;
     };
 
-    for stmt in body {
+    if !keywords.is_empty() {
-        let Stmt::Expr(ast::StmtExpr { value, .. }) = stmt else {
+        return;
-            continue;
+    }
-        };
 
-        let Expr::Call(ast::ExprCall { func, range, .. }) = value.as_ref() else {
+    let [arg] = args.as_slice() else {
-            continue;
+        return;
-        };
+    };
 
-        let Expr::Attribute(ast::ExprAttribute { attr, .. }) = func.as_ref() else {
+    // Ignore direct list copies (e.g., `for x in y: filtered.append(x)`).
-            continue;
+    if !conditional {
-        };
+        if arg.as_name_expr().map_or(false, |arg| {
-
+            target
-        if attr.as_str() == "append" {
+                .as_name_expr()
-            checker
+                .map_or(false, |target| arg.id == target.id)
-                .diagnostics
+        }) {
-                .push(Diagnostic::new(ManualListComprehension, *range));
+            return;
         }
     }
+
+    let Expr::Attribute(ast::ExprAttribute { attr, .. }) = func.as_ref() else {
+        return;
+    };
+
+    if attr.as_str() == "append" {
+        checker
+            .diagnostics
+            .push(Diagnostic::new(ManualListComprehension, *range));
+    }
 }

crates/ruff/src/rules/perflint/rules/manual_list_copy.rs

@@ -44,7 +44,7 @@ impl Violation for ManualListCopy {
 }
 
 /// PERF402
-pub(crate) fn manual_list_copy(checker: &mut Checker, body: &[Stmt]) {
+pub(crate) fn manual_list_copy(checker: &mut Checker, target: &Expr, body: &[Stmt]) {
     let [stmt] = body else {
         return;
     };
@@ -53,10 +53,33 @@ pub(crate) fn manual_list_copy(checker: &mut Checker, body: &[Stmt]) {
         return;
     };
 
-    let Expr::Call(ast::ExprCall { func, range, .. }) = value.as_ref() else {
+    let Expr::Call(ast::ExprCall {
+        func,
+        range,
+        args,
+        keywords,
+    }) = value.as_ref()
+    else {
         return;
     };
 
+    if !keywords.is_empty() {
+        return;
+    }
+
+    let [arg] = args.as_slice() else {
+        return;
+    };
+
+    // Only flag direct list copies (e.g., `for x in y: filtered.append(x)`).
+    if !arg.as_name_expr().map_or(false, |arg| {
+        target
+            .as_name_expr()
+            .map_or(false, |target| arg.id == target.id)
+    }) {
+        return;
+    }
+
     let Expr::Attribute(ast::ExprAttribute { attr, .. }) = func.as_ref() else {
         return;
     };

crates/ruff/src/rules/perflint/snapshots/ruff__rules__perflint__tests__PERF401_PERF401.py.snap

@@ -1,7 +1,7 @@
 ---
 source: crates/ruff/src/rules/perflint/mod.rs
 ---
-PERF401.py:6:13: PERF401 Use a list comprehension to create a new filtered list
+PERF401.py:6:13: PERF401 Use a list comprehension to create a transformed list
   |
 4 |     for i in items:
 5 |         if i % 2:
@@ -9,14 +9,12 @@ PERF401.py:6:13: PERF401 Use a list comprehension to create a new filtered list
   |             ^^^^^^^^^^^^^^^^ PERF401
   |
 
-PERF401.py:14:13: PERF401 Use a list comprehension to create a new filtered list
+PERF401.py:13:9: PERF401 Use a list comprehension to create a transformed list
    |
+11 |     result = []
 12 |     for i in items:
-13 |         if i % 2:
+13 |         result.append(i * i)  # PERF401
-14 |             result.append(i)  # PERF401
+   |         ^^^^^^^^^^^^^^^^^^^^ PERF401
-   |             ^^^^^^^^^^^^^^^^ PERF401
-15 |         elif i % 2:
-16 |             result.append(i)  # PERF401
    |
 
 

crates/ruff/src/rules/perflint/snapshots/ruff__rules__perflint__tests__PERF402_PERF402.py.snap

@@ -9,12 +9,4 @@ PERF402.py:5:9: PERF402 Use `list` or `list.copy` to create a copy of a list
   |         ^^^^^^^^^^^^^^^^ PERF402
   |
 
-PERF402.py:12:9: PERF402 Use `list` or `list.copy` to create a copy of a list
-   |
-10 |     result = []
-11 |     for i in items:
-12 |         result.insert(0, i)  # PERF402
-   |         ^^^^^^^^^^^^^^^^^^^ PERF402
-   |
-