Avoid underflow in expected-special-method-signature (#4377)

crates/ruff/resources/test/fixtures/pylint/unexpected_special_method_signature.py

@@ -1,19 +1,16 @@
 class TestClass:
     def __bool__(self):
         ...
-    
+
     def __bool__(self, x):  # too many mandatory args
         ...
-    
+
     def __bool__(self, x=1):  # additional optional args OK
         ...
-    
+
-    def __bool__(self, *args):  # varargs OK
-        ...
-    
     def __bool__():  # ignored; should be caughty by E0211/N805
         ...
-    
+
     @staticmethod
     def __bool__():
         ...
@@ -21,31 +18,58 @@ class TestClass:
     @staticmethod
     def __bool__(x):  # too many mandatory args
         ...
-    
+
     @staticmethod
     def __bool__(x=1):  # additional optional args OK
         ...
-    
+
     def __eq__(self, other):  # multiple args
         ...
-    
+
     def __eq__(self, other=1):  # expected arg is optional
         ...
-    
+
     def __eq__(self):  # too few mandatory args
         ...
-    
+
     def __eq__(self, other, other_other):  # too many mandatory args
         ...
-    
+
-    def __round__(self):  # allow zero additional args.
+    def __round__(self):  # allow zero additional args
         ...
-    
+
-    def __round__(self, x):  # allow one additional args.
+    def __round__(self, x):  # allow one additional args
         ...
-    
+
     def __round__(self, x, y):  # disallow 2 args
         ...
-    
+
     def __round__(self, x, y, z=2):  # disallow 3 args even when one is optional
-        ...
+        ...
+
+    def __eq__(self, *args):  # ignore *args
+        ...
+
+    def __eq__(self, x, *args):  # extra *args is ok
+        ...
+
+    def __eq__(self, x, y, *args):  # too many args with *args
+        ...
+
+    def __round__(self, *args):  # allow zero additional args
+        ...
+
+    def __round__(self, x, *args):  # allow one additional args
+        ...
+
+    def __round__(self, x, y, *args):  # disallow 2 args
+        ...
+
+    def __eq__(self, **kwargs):  # ignore **kwargs
+        ...
+
+    def __eq__(self, /, other=42):  # ignore positional-only args
+        ...
+
+    def __eq__(self, *, other=42):  # ignore positional-only args
+        ...

crates/ruff/src/rules/pylint/rules/unexpected_special_method_signature.rs

@@ -7,7 +7,6 @@ use ruff_macros::{derive_message_formats, violation};
 use ruff_python_ast::helpers::identifier_range;
 use ruff_python_ast::source_code::Locator;
 use ruff_python_semantic::analyze::visibility::is_staticmethod;
-use ruff_python_semantic::scope::ScopeKind;
 
 use crate::checkers::ast::Checker;
 
@@ -109,7 +108,12 @@ pub fn unexpected_special_method_signature(
     args: &Arguments,
     locator: &Locator,
 ) {
-    if !matches!(checker.ctx.scope().kind, ScopeKind::Class(_)) {
+    if !checker.ctx.scope().kind.is_class() {
+        return;
+    }
+
+    // Ignore methods with positional-only or keyword-only parameters, or variadic parameters.
+    if !args.posonlyargs.is_empty() || !args.kwonlyargs.is_empty() || args.kwarg.is_some() {
         return;
     }
 
@@ -126,18 +130,22 @@ pub fn unexpected_special_method_signature(
         return;
     };
 
-    let emit = match expected_params {
+    let valid_signature = match expected_params {
-        ExpectedParams::Range(min, max) => !(min..=max).contains(&actual_params),
+        ExpectedParams::Range(min, max) => {
-        ExpectedParams::Fixed(expected) => match expected.cmp(&mandatory_params) {
+            if mandatory_params >= min {
-            Ordering::Less => true,
+                mandatory_params <= max
-            Ordering::Greater => {
+            } else {
-                args.vararg.is_none() && optional_params < (expected - mandatory_params)
+                args.vararg.is_some() || actual_params <= max
             }
-            Ordering::Equal => false,
+        }
+        ExpectedParams::Fixed(expected) => match expected.cmp(&mandatory_params) {
+            Ordering::Less => false,
+            Ordering::Greater => args.vararg.is_some() || actual_params >= expected,
+            Ordering::Equal => true,
         },
     };
 
-    if emit {
+    if !valid_signature {
         checker.diagnostics.push(Diagnostic::new(
             UnexpectedSpecialMethodSignature {
                 method_name: name.to_owned(),

crates/ruff/src/rules/pylint/snapshots/ruff__rules__pylint__tests__PLE0302_unexpected_special_method_signature.py.snap

@@ -4,54 +4,72 @@ source: crates/ruff/src/rules/pylint/mod.rs
 unexpected_special_method_signature.py:5:9: PLE0302 The special method `__bool__` expects 1 parameter, 2 were given
   |
 5 |         ...
-6 |     
+6 | 
 7 |     def __bool__(self, x):  # too many mandatory args
   |         ^^^^^^^^ PLE0302
 8 |         ...
   |
 
-unexpected_special_method_signature.py:22:9: PLE0302 The special method `__bool__` expects 0 parameters, 1 was given
+unexpected_special_method_signature.py:19:9: PLE0302 The special method `__bool__` expects 0 parameters, 1 was given
    |
-22 |     @staticmethod
+19 |     @staticmethod
-23 |     def __bool__(x):  # too many mandatory args
+20 |     def __bool__(x):  # too many mandatory args
    |         ^^^^^^^^ PLE0302
-24 |         ...
+21 |         ...
    |
 
-unexpected_special_method_signature.py:35:9: PLE0302 The special method `__eq__` expects 2 parameters, 1 was given
+unexpected_special_method_signature.py:32:9: PLE0302 The special method `__eq__` expects 2 parameters, 1 was given
+   |
+32 |         ...
+33 | 
+34 |     def __eq__(self):  # too few mandatory args
+   |         ^^^^^^ PLE0302
+35 |         ...
+   |
+
+unexpected_special_method_signature.py:35:9: PLE0302 The special method `__eq__` expects 2 parameters, 3 were given
    |
 35 |         ...
-36 |     
+36 | 
-37 |     def __eq__(self):  # too few mandatory args
+37 |     def __eq__(self, other, other_other):  # too many mandatory args
    |         ^^^^^^ PLE0302
 38 |         ...
    |
 
-unexpected_special_method_signature.py:38:9: PLE0302 The special method `__eq__` expects 2 parameters, 3 were given
+unexpected_special_method_signature.py:44:9: PLE0302 The special method `__round__` expects between 1 and 2 parameters, 3 were given
    |
-38 |         ...
+44 |         ...
-39 |     
+45 | 
-40 |     def __eq__(self, other, other_other):  # too many mandatory args
+46 |     def __round__(self, x, y):  # disallow 2 args
-   |         ^^^^^^ PLE0302
+   |         ^^^^^^^^^ PLE0302
-41 |         ...
+47 |         ...
    |
 
-unexpected_special_method_signature.py:47:9: PLE0302 The special method `__round__` expects between 1 and 2 parameters, 3 were given
+unexpected_special_method_signature.py:47:9: PLE0302 The special method `__round__` expects between 1 and 2 parameters, 4 were given
    |
 47 |         ...
-48 |     
+48 | 
-49 |     def __round__(self, x, y):  # disallow 2 args
+49 |     def __round__(self, x, y, z=2):  # disallow 3 args even when one is optional
    |         ^^^^^^^^^ PLE0302
 50 |         ...
    |
 
-unexpected_special_method_signature.py:50:9: PLE0302 The special method `__round__` expects between 1 and 2 parameters, 4 were given
+unexpected_special_method_signature.py:56:9: PLE0302 The special method `__eq__` expects 2 parameters, 3 were given
    |
-50 |         ...
+56 |         ...
-51 |     
+57 | 
-52 |     def __round__(self, x, y, z=2):  # disallow 3 args even when one is optional
+58 |     def __eq__(self, x, y, *args):  # too many args with *args
+   |         ^^^^^^ PLE0302
+59 |         ...
+   |
+
+unexpected_special_method_signature.py:65:9: PLE0302 The special method `__round__` expects between 1 and 2 parameters, 3 were given
+   |
+65 |         ...
+66 | 
+67 |     def __round__(self, x, y, *args):  # disallow 2 args
    |         ^^^^^^^^^ PLE0302
-53 |         ...
+68 |         ...
    |