[pylint] Implement invalid-bytes-returned (E0308) (#10959)

Add pylint rule invalid-bytes-returned (PLE0308)

See https://github.com/astral-sh/ruff/issues/970 for rules

Test Plan: `cargo test`

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

@@ -0,0 +1,65 @@
+# These testcases should raise errors
+
+
+class Float:
+    def __bytes__(self):
+        return 3.05  # [invalid-bytes-return]
+
+
+class Int:
+    def __bytes__(self):
+        return 0  # [invalid-bytes-return]
+
+
+class Str:
+    def __bytes__(self):
+        return "some bytes"  # [invalid-bytes-return]
+
+
+class BytesNoReturn:
+    def __bytes__(self):
+        print("ruff")  # [invalid-bytes-return]
+
+
+class BytesWrongRaise:
+    def __bytes__(self):
+        print("raise some error")
+        raise NotImplementedError  # [invalid-bytes-return]
+
+
+# TODO: Once Ruff has better type checking
+def return_bytes():
+    return "some string"
+
+
+class ComplexReturn:
+    def __bytes__(self):
+        return return_bytes()  # [invalid-bytes-return]
+
+
+# These testcases should NOT raise errors
+
+
+class Bytes:
+    def __bytes__(self):
+        return b"some bytes"
+
+
+class Bytes2:
+    def __bytes__(self):
+        x = b"some bytes"
+        return x
+
+
+class Bytes3:
+    def __bytes__(self): ...
+
+
+class Bytes4:
+    def __bytes__(self):
+        pass
+
+
+class Bytes5:
+    def __bytes__(self):
+        raise NotImplementedError

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

@@ -97,6 +97,9 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
             if checker.enabled(Rule::InvalidBoolReturnType) {
                 pylint::rules::invalid_bool_return(checker, name, body);
             }
+            if checker.enabled(Rule::InvalidBytesReturnType) {
+                pylint::rules::invalid_bytes_return(checker, function_def);
+            }
             if checker.enabled(Rule::InvalidStrReturnType) {
                 pylint::rules::invalid_str_return(checker, name, body);
             }

crates/ruff_linter/src/codes.rs

@@ -243,6 +243,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Pylint, "E0302") => (RuleGroup::Stable, rules::pylint::rules::UnexpectedSpecialMethodSignature),
         (Pylint, "E0304") => (RuleGroup::Preview, rules::pylint::rules::InvalidBoolReturnType),
         (Pylint, "E0307") => (RuleGroup::Stable, rules::pylint::rules::InvalidStrReturnType),
+        (Pylint, "E0308") => (RuleGroup::Preview, rules::pylint::rules::InvalidBytesReturnType),
         (Pylint, "E0604") => (RuleGroup::Stable, rules::pylint::rules::InvalidAllObject),
         (Pylint, "E0605") => (RuleGroup::Stable, rules::pylint::rules::InvalidAllFormat),
         (Pylint, "E0643") => (RuleGroup::Preview, rules::pylint::rules::PotentialIndexError),

crates/ruff_linter/src/rules/flake8_bugbear/rules/mutable_argument_default.rs

@@ -1,10 +1,11 @@
 use ruff_diagnostics::{Diagnostic, Edit, Fix, FixAvailability, Violation};
 use ruff_macros::{derive_message_formats, violation};
-use ruff_python_ast::helpers::{is_docstring_stmt, map_callable};
+use ruff_python_ast::helpers::is_docstring_stmt;
 use ruff_python_ast::name::QualifiedName;
-use ruff_python_ast::{self as ast, Expr, Parameter, ParameterWithDefault, Stmt, StmtRaise};
+use ruff_python_ast::{self as ast, Expr, Parameter, ParameterWithDefault};
 use ruff_python_codegen::{Generator, Stylist};
 use ruff_python_index::Indexer;
+use ruff_python_semantic::analyze::function_type::is_stub;
 use ruff_python_semantic::analyze::typing::{is_immutable_annotation, is_mutable_expr};
 use ruff_python_semantic::SemanticModel;
 use ruff_python_trivia::{indentation_at_offset, textwrap};
@@ -213,29 +214,3 @@ fn move_initialization(
     let initialization_edit = Edit::insertion(content, pos);
     Some(Fix::unsafe_edits(default_edit, [initialization_edit]))
 }
-
-/// Returns `true` if a function has an empty body, and is therefore a stub.
-///
-/// A function body is considered to be empty if it contains only `pass` statements, `...` literals,
-/// `NotImplementedError` raises, or string literal statements (docstrings).
-fn is_stub(function_def: &ast::StmtFunctionDef, semantic: &SemanticModel) -> bool {
-    function_def.body.iter().all(|stmt| match stmt {
-        Stmt::Pass(_) => true,
-        Stmt::Expr(ast::StmtExpr { value, range: _ }) => {
-            matches!(
-                value.as_ref(),
-                Expr::StringLiteral(_) | Expr::EllipsisLiteral(_)
-            )
-        }
-        Stmt::Raise(StmtRaise {
-            range: _,
-            exc: exception,
-            cause: _,
-        }) => exception.as_ref().is_some_and(|exc| {
-            semantic
-                .resolve_builtin_symbol(map_callable(exc))
-                .is_some_and(|name| matches!(name, "NotImplementedError" | "NotImplemented"))
-        }),
-        _ => false,
-    })
-}

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

@@ -77,6 +77,10 @@ mod tests {
     #[test_case(Rule::InvalidAllFormat, Path::new("invalid_all_format.py"))]
     #[test_case(Rule::InvalidAllObject, Path::new("invalid_all_object.py"))]
     #[test_case(Rule::InvalidBoolReturnType, Path::new("invalid_return_type_bool.py"))]
+    #[test_case(
+        Rule::InvalidBytesReturnType,
+        Path::new("invalid_return_type_bytes.py")
+    )]
     #[test_case(Rule::InvalidStrReturnType, Path::new("invalid_return_type_str.py"))]
     #[test_case(Rule::DuplicateBases, Path::new("duplicate_bases.py"))]
     #[test_case(Rule::InvalidCharacterBackspace, Path::new("invalid_characters.py"))]

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

@@ -0,0 +1,90 @@
+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::{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;
+
+use crate::checkers::ast::Checker;
+
+/// ## What it does
+/// Checks for `__bytes__` implementations that return a type other than `bytes`.
+///
+/// ## Why is this bad?
+/// The `__bytes__` method should return a `bytes` object. Returning a different
+/// type may cause unexpected behavior.
+///
+/// ## Example
+/// ```python
+/// class Foo:
+///     def __bytes__(self):
+///         return 2
+/// ```
+///
+/// Use instead:
+/// ```python
+/// class Foo:
+///     def __bytes__(self):
+///         return b"2"
+/// ```
+///
+/// ## References
+/// - [Python documentation: The `__bytes__` method](https://docs.python.org/3/reference/datamodel.html#object.__bytes__)
+#[violation]
+pub struct InvalidBytesReturnType;
+
+impl Violation for InvalidBytesReturnType {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        format!("`__bytes__` does not return `bytes`")
+    }
+}
+
+/// E0308
+pub(crate) fn invalid_bytes_return(checker: &mut Checker, function_def: &ast::StmtFunctionDef) {
+    if function_def.name.as_str() != "__bytes__" {
+        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(&function_def.body);
+        visitor.returns
+    };
+
+    if returns.is_empty() {
+        checker.diagnostics.push(Diagnostic::new(
+            InvalidBytesReturnType,
+            function_def.identifier(),
+        ));
+    }
+
+    for stmt in returns {
+        if let Some(value) = stmt.value.as_deref() {
+            if !matches!(
+                ResolvedPythonType::from(value),
+                ResolvedPythonType::Unknown | ResolvedPythonType::Atom(PythonType::Bytes)
+            ) {
+                checker
+                    .diagnostics
+                    .push(Diagnostic::new(InvalidBytesReturnType, value.range()));
+            }
+        } else {
+            // Disallow implicit `None`.
+            checker
+                .diagnostics
+                .push(Diagnostic::new(InvalidBytesReturnType, stmt.range()));
+        }
+    }
+}

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

@@ -28,6 +28,7 @@ pub(crate) use import_self::*;
 pub(crate) use invalid_all_format::*;
 pub(crate) use invalid_all_object::*;
 pub(crate) use invalid_bool_return::*;
+pub(crate) use invalid_bytes_return::*;
 pub(crate) use invalid_envvar_default::*;
 pub(crate) use invalid_envvar_value::*;
 pub(crate) use invalid_str_return::*;
@@ -126,6 +127,7 @@ mod import_self;
 mod invalid_all_format;
 mod invalid_all_object;
 mod invalid_bool_return;
+mod invalid_bytes_return;
 mod invalid_envvar_default;
 mod invalid_envvar_value;
 mod invalid_str_return;

crates/ruff_linter/src/rules/pylint/snapshots/ruff_linter__rules__pylint__tests__PLE0308_invalid_return_type_bytes.py.snap

@@ -0,0 +1,43 @@
+---
+source: crates/ruff_linter/src/rules/pylint/mod.rs
+---
+invalid_return_type_bytes.py:6:16: PLE0308 `__bytes__` does not return `bytes`
+  |
+4 | class Float:
+5 |     def __bytes__(self):
+6 |         return 3.05  # [invalid-bytes-return]
+  |                ^^^^ PLE0308
+  |
+
+invalid_return_type_bytes.py:11:16: PLE0308 `__bytes__` does not return `bytes`
+   |
+ 9 | class Int:
+10 |     def __bytes__(self):
+11 |         return 0  # [invalid-bytes-return]
+   |                ^ PLE0308
+   |
+
+invalid_return_type_bytes.py:16:16: PLE0308 `__bytes__` does not return `bytes`
+   |
+14 | class Str:
+15 |     def __bytes__(self):
+16 |         return "some bytes"  # [invalid-bytes-return]
+   |                ^^^^^^^^^^^^ PLE0308
+   |
+
+invalid_return_type_bytes.py:20:9: PLE0308 `__bytes__` does not return `bytes`
+   |
+19 | class BytesNoReturn:
+20 |     def __bytes__(self):
+   |         ^^^^^^^^^ PLE0308
+21 |         print("ruff")  # [invalid-bytes-return]
+   |
+
+invalid_return_type_bytes.py:25:9: PLE0308 `__bytes__` does not return `bytes`
+   |
+24 | class BytesWrongRaise:
+25 |     def __bytes__(self):
+   |         ^^^^^^^^^ PLE0308
+26 |         print("raise some error")
+27 |         raise NotImplementedError  # [invalid-bytes-return]
+   |

crates/ruff_python_semantic/src/analyze/function_type.rs

@@ -1,6 +1,6 @@
 use ruff_python_ast::helpers::map_callable;
 use ruff_python_ast::name::{QualifiedName, UnqualifiedName};
-use ruff_python_ast::Decorator;
+use ruff_python_ast::{Decorator, Expr, Stmt, StmtExpr, StmtFunctionDef, StmtRaise};
 
 use crate::model::SemanticModel;
 use crate::scope::{Scope, ScopeKind};
@@ -128,3 +128,29 @@ fn is_class_method(
 
     false
 }
+
+/// Returns `true` if a function has an empty body, and is therefore a stub.
+///
+/// A function body is considered to be empty if it contains only `pass` statements, `...` literals,
+/// `NotImplementedError` raises, or string literal statements (docstrings).
+pub fn is_stub(function_def: &StmtFunctionDef, semantic: &SemanticModel) -> bool {
+    function_def.body.iter().all(|stmt| match stmt {
+        Stmt::Pass(_) => true,
+        Stmt::Expr(StmtExpr { value, range: _ }) => {
+            matches!(
+                value.as_ref(),
+                Expr::StringLiteral(_) | Expr::EllipsisLiteral(_)
+            )
+        }
+        Stmt::Raise(StmtRaise {
+            range: _,
+            exc: exception,
+            cause: _,
+        }) => exception.as_ref().is_some_and(|exc| {
+            semantic
+                .resolve_builtin_symbol(map_callable(exc))
+                .is_some_and(|name| matches!(name, "NotImplementedError" | "NotImplemented"))
+        }),
+        _ => false,
+    })
+}

ruff.schema.json

@@ -3269,6 +3269,7 @@
         "PLE0302",
         "PLE0304",
         "PLE0307",
+        "PLE0308",
         "PLE06",
         "PLE060",
         "PLE0604",