Avoid ANN2xx autofix for abstract methods with empty body (#9034)

## Summary

This PR updates the `ANN201`, `ANN202`, `ANN205`, and `ANN206` rules to
not create a fix for the return type when it's an abstract method and
the function body is empty i.e., it only contains either a pass
statement, docstring or an ellipsis literal.

fixes: #9004

## Test Plan

Add the following test cases:
- Abstract method with pass statement
- Abstract method with docstring
- Abstract method with ellipsis literal
- Abstract method with possible return type

crates/ruff_linter/resources/test/fixtures/flake8_annotations/auto_return_type.py

@@ -147,3 +147,38 @@ def func(x: int):
     while x > 0:
         break
         return 1
+
+
+import abc
+from abc import abstractmethod
+
+
+class Foo(abc.ABC):
+    @abstractmethod
+    def method(self):
+        pass
+
+    @abc.abstractmethod
+    def method(self):
+        """Docstring."""
+
+    @abc.abstractmethod
+    def method(self):
+        ...
+
+    @staticmethod
+    @abstractmethod
+    def method():
+        pass
+
+    @classmethod
+    @abstractmethod
+    def method(cls):
+        pass
+
+    @abstractmethod
+    def method(self):
+        if self.x > 0:
+            return 1
+        else:
+            return 1.5

crates/ruff_linter/src/rules/flake8_annotations/rules/definition.rs

@@ -537,6 +537,19 @@ fn check_dynamically_typed<F>(
     }
 }
 
+fn is_empty_body(body: &[Stmt]) -> bool {
+    body.iter().all(|stmt| match stmt {
+        Stmt::Pass(_) => true,
+        Stmt::Expr(ast::StmtExpr { value, range: _ }) => {
+            matches!(
+                value.as_ref(),
+                Expr::StringLiteral(_) | Expr::EllipsisLiteral(_)
+            )
+        }
+        _ => false,
+    })
+}
+
 /// Generate flake8-annotation checks for a given `Definition`.
 pub(crate) fn definition(
     checker: &Checker,
@@ -725,7 +738,12 @@ pub(crate) fn definition(
     ) {
         if is_method && visibility::is_classmethod(decorator_list, checker.semantic()) {
             if checker.enabled(Rule::MissingReturnTypeClassMethod) {
-                let return_type = auto_return_type(function)
+                let return_type = if visibility::is_abstract(decorator_list, checker.semantic())
+                    && is_empty_body(body)
+                {
+                    None
+                } else {
+                    auto_return_type(function)
                         .and_then(|return_type| {
                             return_type.into_expression(
                                 checker.importer(),
@@ -734,7 +752,8 @@ pub(crate) fn definition(
                                 checker.settings.target_version,
                             )
                         })
-                    .map(|(return_type, edits)| (checker.generator().expr(&return_type), edits));
+                        .map(|(return_type, edits)| (checker.generator().expr(&return_type), edits))
+                };
                 let mut diagnostic = Diagnostic::new(
                     MissingReturnTypeClassMethod {
                         name: name.to_string(),
@@ -752,7 +771,12 @@ pub(crate) fn definition(
             }
         } else if is_method && visibility::is_staticmethod(decorator_list, checker.semantic()) {
             if checker.enabled(Rule::MissingReturnTypeStaticMethod) {
-                let return_type = auto_return_type(function)
+                let return_type = if visibility::is_abstract(decorator_list, checker.semantic())
+                    && is_empty_body(body)
+                {
+                    None
+                } else {
+                    auto_return_type(function)
                         .and_then(|return_type| {
                             return_type.into_expression(
                                 checker.importer(),
@@ -761,7 +785,8 @@ pub(crate) fn definition(
                                 checker.settings.target_version,
                             )
                         })
-                    .map(|(return_type, edits)| (checker.generator().expr(&return_type), edits));
+                        .map(|(return_type, edits)| (checker.generator().expr(&return_type), edits))
+                };
                 let mut diagnostic = Diagnostic::new(
                     MissingReturnTypeStaticMethod {
                         name: name.to_string(),
@@ -818,7 +843,13 @@ pub(crate) fn definition(
             match visibility {
                 visibility::Visibility::Public => {
                     if checker.enabled(Rule::MissingReturnTypeUndocumentedPublicFunction) {
-                        let return_type = auto_return_type(function)
+                        let return_type =
+                            if visibility::is_abstract(decorator_list, checker.semantic())
+                                && is_empty_body(body)
+                            {
+                                None
+                            } else {
+                                auto_return_type(function)
                                     .and_then(|return_type| {
                                         return_type.into_expression(
                                             checker.importer(),
@@ -829,7 +860,8 @@ pub(crate) fn definition(
                                     })
                                     .map(|(return_type, edits)| {
                                         (checker.generator().expr(&return_type), edits)
-                            });
+                                    })
+                            };
                         let mut diagnostic = Diagnostic::new(
                             MissingReturnTypeUndocumentedPublicFunction {
                                 name: name.to_string(),
@@ -853,7 +885,13 @@ pub(crate) fn definition(
                 }
                 visibility::Visibility::Private => {
                     if checker.enabled(Rule::MissingReturnTypePrivateFunction) {
-                        let return_type = auto_return_type(function)
+                        let return_type =
+                            if visibility::is_abstract(decorator_list, checker.semantic())
+                                && is_empty_body(body)
+                            {
+                                None
+                            } else {
+                                auto_return_type(function)
                                     .and_then(|return_type| {
                                         return_type.into_expression(
                                             checker.importer(),
@@ -864,7 +902,8 @@ pub(crate) fn definition(
                                     })
                                     .map(|(return_type, edits)| {
                                         (checker.generator().expr(&return_type), edits)
-                            });
+                                    })
+                            };
                         let mut diagnostic = Diagnostic::new(
                             MissingReturnTypePrivateFunction {
                                 name: name.to_string(),

crates/ruff_linter/src/rules/flake8_annotations/snapshots/ruff_linter__rules__flake8_annotations__tests__auto_return_type.snap

@@ -427,4 +427,72 @@ auto_return_type.py:146:5: ANN201 [*] Missing return type annotation for public
 148 148 |         break
 149 149 |         return 1
 
+auto_return_type.py:158:9: ANN201 Missing return type annotation for public function `method`
+    |
+156 | class Foo(abc.ABC):
+157 |     @abstractmethod
+158 |     def method(self):
+    |         ^^^^^^ ANN201
+159 |         pass
+    |
+    = help: Add return type annotation
+
+auto_return_type.py:162:9: ANN201 Missing return type annotation for public function `method`
+    |
+161 |     @abc.abstractmethod
+162 |     def method(self):
+    |         ^^^^^^ ANN201
+163 |         """Docstring."""
+    |
+    = help: Add return type annotation
+
+auto_return_type.py:166:9: ANN201 Missing return type annotation for public function `method`
+    |
+165 |     @abc.abstractmethod
+166 |     def method(self):
+    |         ^^^^^^ ANN201
+167 |         ...
+    |
+    = help: Add return type annotation
+
+auto_return_type.py:171:9: ANN205 Missing return type annotation for staticmethod `method`
+    |
+169 |     @staticmethod
+170 |     @abstractmethod
+171 |     def method():
+    |         ^^^^^^ ANN205
+172 |         pass
+    |
+    = help: Add return type annotation
+
+auto_return_type.py:176:9: ANN206 Missing return type annotation for classmethod `method`
+    |
+174 |     @classmethod
+175 |     @abstractmethod
+176 |     def method(cls):
+    |         ^^^^^^ ANN206
+177 |         pass
+    |
+    = help: Add return type annotation
+
+auto_return_type.py:180:9: ANN201 [*] Missing return type annotation for public function `method`
+    |
+179 |     @abstractmethod
+180 |     def method(self):
+    |         ^^^^^^ ANN201
+181 |         if self.x > 0:
+182 |             return 1
+    |
+    = help: Add return type annotation: `float`
+
+ℹ Unsafe fix
+177 177 |         pass
+178 178 | 
+179 179 |     @abstractmethod
+180     |-    def method(self):
+    180 |+    def method(self) -> float:
+181 181 |         if self.x > 0:
+182 182 |             return 1
+183 183 |         else:
+
 

crates/ruff_linter/src/rules/flake8_annotations/snapshots/ruff_linter__rules__flake8_annotations__tests__auto_return_type_py38.snap

@@ -482,4 +482,72 @@ auto_return_type.py:146:5: ANN201 [*] Missing return type annotation for public
 148 149 |         break
 149 150 |         return 1
 
+auto_return_type.py:158:9: ANN201 Missing return type annotation for public function `method`
+    |
+156 | class Foo(abc.ABC):
+157 |     @abstractmethod
+158 |     def method(self):
+    |         ^^^^^^ ANN201
+159 |         pass
+    |
+    = help: Add return type annotation
+
+auto_return_type.py:162:9: ANN201 Missing return type annotation for public function `method`
+    |
+161 |     @abc.abstractmethod
+162 |     def method(self):
+    |         ^^^^^^ ANN201
+163 |         """Docstring."""
+    |
+    = help: Add return type annotation
+
+auto_return_type.py:166:9: ANN201 Missing return type annotation for public function `method`
+    |
+165 |     @abc.abstractmethod
+166 |     def method(self):
+    |         ^^^^^^ ANN201
+167 |         ...
+    |
+    = help: Add return type annotation
+
+auto_return_type.py:171:9: ANN205 Missing return type annotation for staticmethod `method`
+    |
+169 |     @staticmethod
+170 |     @abstractmethod
+171 |     def method():
+    |         ^^^^^^ ANN205
+172 |         pass
+    |
+    = help: Add return type annotation
+
+auto_return_type.py:176:9: ANN206 Missing return type annotation for classmethod `method`
+    |
+174 |     @classmethod
+175 |     @abstractmethod
+176 |     def method(cls):
+    |         ^^^^^^ ANN206
+177 |         pass
+    |
+    = help: Add return type annotation
+
+auto_return_type.py:180:9: ANN201 [*] Missing return type annotation for public function `method`
+    |
+179 |     @abstractmethod
+180 |     def method(self):
+    |         ^^^^^^ ANN201
+181 |         if self.x > 0:
+182 |             return 1
+    |
+    = help: Add return type annotation: `float`
+
+ℹ Unsafe fix
+177 177 |         pass
+178 178 | 
+179 179 |     @abstractmethod
+180     |-    def method(self):
+    180 |+    def method(self) -> float:
+181 181 |         if self.x > 0:
+182 182 |             return 1
+183 183 |         else:
+