[pylint] Omit stubs from invalid-bool and invalid-str-return-type (#11008)

## Summary

Reflecting some improvements that were made in
#10959.

Author: charliermarsh

crates/ruff_linter/resources/test/fixtures/pylint/invalid_return_type_str.py

@@ -1,36 +1,49 @@
 # These testcases should raise errors
 
+
 class Float:
     def __str__(self):
         return 3.05
 
+
 class Int:
     def __str__(self):
         return 1
 
+
 class Int2:
     def __str__(self):
         return 0
 
+
 class Bool:
     def __str__(self):
         return False
 
+
 # TODO: Once Ruff has better type checking
 def return_int():
     return 3
 
+
 class ComplexReturn:
     def __str__(self):
         return return_int()
 
+
 # These testcases should NOT raise errors
 
+
 class Str:
     def __str__(self):
         return "ruff"
 
+
 class Str2:
     def __str__(self):
         x = "ruff"
         return x
+
+
+class Str3:
+    def __str__(self): ...

crates/ruff_linter/src/checkers/ast/analyze/statement.rs

@@ -95,7 +95,7 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
                 }
             }
             if checker.enabled(Rule::InvalidBoolReturnType) {
-                pylint::rules::invalid_bool_return(checker, name, body);
+                pylint::rules::invalid_bool_return(checker, function_def);
             }
             if checker.enabled(Rule::InvalidLengthReturnType) {
                 pylint::rules::invalid_length_return(checker, function_def);
@@ -104,7 +104,7 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
                 pylint::rules::invalid_bytes_return(checker, function_def);
             }
             if checker.enabled(Rule::InvalidStrReturnType) {
-                pylint::rules::invalid_str_return(checker, name, body);
+                pylint::rules::invalid_str_return(checker, function_def);
             }
             if checker.enabled(Rule::InvalidFunctionName) {
                 if let Some(diagnostic) = pep8_naming::rules::invalid_function_name(

crates/ruff_linter/src/rules/pylint/rules/invalid_bool_return.rs

@@ -1,8 +1,10 @@
 use ruff_diagnostics::{Diagnostic, Violation};
 use ruff_macros::{derive_message_formats, violation};
 use ruff_python_ast::helpers::ReturnStatementVisitor;
+use ruff_python_ast::identifier::Identifier;
 use ruff_python_ast::visitor::Visitor;
-use ruff_python_ast::Stmt;
+use ruff_python_ast::{self as ast};
+use ruff_python_semantic::analyze::function_type::is_stub;
 use ruff_python_semantic::analyze::type_inference::{NumberLike, PythonType, ResolvedPythonType};
 use ruff_text_size::Ranged;
 
@@ -42,21 +44,32 @@ impl Violation for InvalidBoolReturnType {
 }
 
 /// E0307
-pub(crate) fn invalid_bool_return(checker: &mut Checker, name: &str, body: &[Stmt]) {
-    if name != "__bool__" {
+pub(crate) fn invalid_bool_return(checker: &mut Checker, function_def: &ast::StmtFunctionDef) {
+    if function_def.name.as_str() != "__bool__" {
         return;
     }
 
     if !checker.semantic().current_scope().kind.is_class() {
         return;
     }
 
+    if is_stub(function_def, checker.semantic()) {
+        return;
+    }
+
     let returns = {
         let mut visitor = ReturnStatementVisitor::default();
-        visitor.visit_body(body);
+        visitor.visit_body(&function_def.body);
         visitor.returns
     };
 
+    if returns.is_empty() {
+        checker.diagnostics.push(Diagnostic::new(
+            InvalidBoolReturnType,
+            function_def.identifier(),
+        ));
+    }
+
     for stmt in returns {
         if let Some(value) = stmt.value.as_deref() {
             if !matches!(

crates/ruff_linter/src/rules/pylint/rules/invalid_str_return.rs

@@ -1,8 +1,10 @@
 use ruff_diagnostics::{Diagnostic, Violation};
 use ruff_macros::{derive_message_formats, violation};
 use ruff_python_ast::helpers::ReturnStatementVisitor;
+use ruff_python_ast::identifier::Identifier;
 use ruff_python_ast::visitor::Visitor;
-use ruff_python_ast::Stmt;
+use ruff_python_ast::{self as ast};
+use ruff_python_semantic::analyze::function_type::is_stub;
 use ruff_python_semantic::analyze::type_inference::{PythonType, ResolvedPythonType};
 use ruff_text_size::Ranged;
 
@@ -42,21 +44,32 @@ impl Violation for InvalidStrReturnType {
 }
 
 /// E0307
-pub(crate) fn invalid_str_return(checker: &mut Checker, name: &str, body: &[Stmt]) {
-    if name != "__str__" {
+pub(crate) fn invalid_str_return(checker: &mut Checker, function_def: &ast::StmtFunctionDef) {
+    if function_def.name.as_str() != "__str__" {
         return;
     }
 
     if !checker.semantic().current_scope().kind.is_class() {
         return;
     }
 
+    if is_stub(function_def, checker.semantic()) {
+        return;
+    }
+
     let returns = {
         let mut visitor = ReturnStatementVisitor::default();
-        visitor.visit_body(body);
+        visitor.visit_body(&function_def.body);
         visitor.returns
     };
 
+    if returns.is_empty() {
+        checker.diagnostics.push(Diagnostic::new(
+            InvalidStrReturnType,
+            function_def.identifier(),
+        ));
+    }
+
     for stmt in returns {
         if let Some(value) = stmt.value.as_deref() {
             if !matches!(

crates/ruff_linter/src/rules/pylint/snapshots/ruff_linter__rules__pylint__tests__PLE0307_invalid_return_type_str.py.snap

@@ -1,42 +1,34 @@
 ---
 source: crates/ruff_linter/src/rules/pylint/mod.rs
 ---
-invalid_return_type_str.py:5:16: PLE0307 `__str__` does not return `str`
+invalid_return_type_str.py:6:16: PLE0307 `__str__` does not return `str`
   |
-3 | class Float:
-4 |     def __str__(self):
-5 |         return 3.05
+4 | class Float:
+5 |     def __str__(self):
+6 |         return 3.05
   |                ^^^^ PLE0307
-6 | 
-7 | class Int:
   |
 
-invalid_return_type_str.py:9:16: PLE0307 `__str__` does not return `str`
+invalid_return_type_str.py:11:16: PLE0307 `__str__` does not return `str`
    |
- 7 | class Int:
- 8 |     def __str__(self):
- 9 |         return 1
+ 9 | class Int:
+10 |     def __str__(self):
+11 |         return 1
    |                ^ PLE0307
-10 | 
-11 | class Int2:
    |
 
-invalid_return_type_str.py:13:16: PLE0307 `__str__` does not return `str`
+invalid_return_type_str.py:16:16: PLE0307 `__str__` does not return `str`
    |
-11 | class Int2:
-12 |     def __str__(self):
-13 |         return 0
+14 | class Int2:
+15 |     def __str__(self):
+16 |         return 0
    |                ^ PLE0307
-14 | 
-15 | class Bool:
    |
 
-invalid_return_type_str.py:17:16: PLE0307 `__str__` does not return `str`
+invalid_return_type_str.py:21:16: PLE0307 `__str__` does not return `str`
    |
-15 | class Bool:
-16 |     def __str__(self):
-17 |         return False
+19 | class Bool:
+20 |     def __str__(self):
+21 |         return False
    |                ^^^^^ PLE0307
-18 | 
-19 | # TODO: Once Ruff has better type checking
    |