[pylint] Implement useless-exception-statement (W0133)

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

@@ -0,0 +1,116 @@
+# Test case 1: Useless exception statement
+from abc import ABC, abstractmethod
+from contextlib import suppress
+
+
+def func():
+    AssertionError("This is an assertion error")  # PLW0133
+
+
+# Test case 2: Useless exception statement in try-except block
+def func():
+    try:
+        Exception("This is an exception")  # PLW0133
+    except Exception as err:
+        pass
+
+
+# Test case 3: Useless exception statement in if statement
+def func():
+    if True:
+        RuntimeError("This is an exception")  # PLW0133
+
+
+# Test case 4: Useless exception statement in class
+def func():
+    class Class:
+        def __init__(self):
+            TypeError("This is an exception")  # PLW0133
+
+
+# Test case 5: Useless exception statement in function
+def func():
+    def inner():
+        IndexError("This is an exception")  # PLW0133
+
+    inner()
+
+
+# Test case 6: Useless exception statement in while loop
+def func():
+    while True:
+        KeyError("This is an exception")  # PLW0133
+
+
+# Test case 7: Useless exception statement in abstract class
+def func():
+    class Class(ABC):
+        @abstractmethod
+        def method(self):
+            NotImplementedError("This is an exception")  # PLW0133
+
+
+# Test case 8: Useless exception statement inside context manager
+def func():
+    with suppress(AttributeError):
+        AttributeError("This is an exception")  # PLW0133
+
+
+# Test case 9: Useless exception statement in parentheses
+def func():
+    (RuntimeError("This is an exception"))  # PLW0133
+
+
+# Test case 10: Useless exception statement in continuation
+def func():
+    x = 1; (RuntimeError("This is an exception")); y = 2  # PLW0133
+
+
+# Non-violation test cases: PLW0133
+
+
+# Test case 1: Used exception statement in try-except block
+def func():
+    raise Exception("This is an exception")  # OK
+
+
+# Test case 2: Used exception statement in if statement
+def func():
+    if True:
+        raise ValueError("This is an exception")  # OK
+
+
+# Test case 3: Used exception statement in class
+def func():
+    class Class:
+        def __init__(self):
+            raise TypeError("This is an exception")  # OK
+
+
+# Test case 4: Exception statement used in list comprehension
+def func():
+    [ValueError("This is an exception") for i in range(10)]  # OK
+
+
+# Test case 5: Exception statement used when initializing a dictionary
+def func():
+    {i: TypeError("This is an exception") for i in range(10)}  # OK
+
+
+# Test case 6: Exception statement used in function
+def func():
+    def inner():
+        raise IndexError("This is an exception")  # OK
+
+    inner()
+
+
+# Test case 7: Exception statement used in variable assignment
+def func():
+    err = KeyError("This is an exception")  # OK
+
+
+# Test case 8: Exception statement inside context manager
+def func():
+    with suppress(AttributeError):
+        raise AttributeError("This is an exception")  # OK

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

@@ -1609,7 +1609,7 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
                 refurb::rules::delete_full_slice(checker, delete);
             }
         }
-        Stmt::Expr(ast::StmtExpr { value, range: _ }) => {
+        Stmt::Expr(expr @ ast::StmtExpr { value, range: _ }) => {
             if checker.enabled(Rule::UselessComparison) {
                 flake8_bugbear::rules::useless_comparison(checker, value);
             }
@@ -1632,6 +1632,9 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
             if checker.enabled(Rule::RepeatedAppend) {
                 refurb::rules::repeated_append(checker, stmt);
             }
+            if checker.enabled(Rule::UselessExceptionStatement) {
+                pylint::rules::useless_exception_statement(checker, expr);
+            }
         }
         _ => {}
     }

crates/ruff_linter/src/codes.rs

@@ -292,6 +292,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Pylint, "W0127") => (RuleGroup::Stable, rules::pylint::rules::SelfAssigningVariable),
         (Pylint, "W0129") => (RuleGroup::Stable, rules::pylint::rules::AssertOnStringLiteral),
         (Pylint, "W0131") => (RuleGroup::Stable, rules::pylint::rules::NamedExprWithoutContext),
+        (Pylint, "W0133") => (RuleGroup::Preview, rules::pylint::rules::UselessExceptionStatement),
         (Pylint, "W0245") => (RuleGroup::Preview, rules::pylint::rules::SuperWithoutBrackets),
         (Pylint, "W0406") => (RuleGroup::Stable, rules::pylint::rules::ImportSelf),
         (Pylint, "W0602") => (RuleGroup::Stable, rules::pylint::rules::GlobalVariableNotAssigned),

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

@@ -176,6 +176,10 @@ mod tests {
         Rule::UnnecessaryDictIndexLookup,
         Path::new("unnecessary_dict_index_lookup.py")
     )]
+    #[test_case(
+        Rule::UselessExceptionStatement,
+        Path::new("useless_exception_statement.py")
+    )]
     fn rules(rule_code: Rule, path: &Path) -> Result<()> {
         let snapshot = format!("{}_{}", rule_code.noqa_code(), path.to_string_lossy());
         let diagnostics = test_path(

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

@@ -78,6 +78,7 @@ pub(crate) use unnecessary_lambda::*;
 pub(crate) use unnecessary_list_index_lookup::*;
 pub(crate) use unspecified_encoding::*;
 pub(crate) use useless_else_on_loop::*;
+pub(crate) use useless_exception_statement::*;
 pub(crate) use useless_import_alias::*;
 pub(crate) use useless_return::*;
 pub(crate) use useless_with_lock::*;
@@ -164,6 +165,7 @@ mod unnecessary_lambda;
 mod unnecessary_list_index_lookup;
 mod unspecified_encoding;
 mod useless_else_on_loop;
+mod useless_exception_statement;
 mod useless_import_alias;
 mod useless_return;
 mod useless_with_lock;

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

@@ -0,0 +1,95 @@
+use ruff_diagnostics::{Diagnostic, Edit, Fix, FixAvailability, Violation};
+use ruff_macros::{derive_message_formats, violation};
+use ruff_python_ast::{self as ast, Expr};
+use ruff_python_semantic::SemanticModel;
+use ruff_text_size::Ranged;
+
+use crate::checkers::ast::Checker;
+
+/// ## What it does
+/// Checks for an exception that is not raised.
+///
+/// ## Why is this bad?
+/// It's unnecessary to create an exception without raising it. For example,
+/// `ValueError("...")` on its own will have no effect (unlike
+/// `raise ValueError("...")`) and is likely a mistake.
+///
+/// ## Example
+/// ```python
+/// ValueError("...")
+/// ```
+///
+/// Use instead:
+/// ```python
+/// raise ValueError("...")
+/// ```
+///
+/// ## Fix safety
+/// This rule's fix is marked as unsafe, as converting a useless exception
+/// statement to a `raise` statement will change the program's behavior.
+#[violation]
+pub struct UselessExceptionStatement;
+
+impl Violation for UselessExceptionStatement {
+    const FIX_AVAILABILITY: FixAvailability = FixAvailability::Sometimes;
+
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        format!("Missing `raise` statement on exception")
+    }
+
+    fn fix_title(&self) -> Option<String> {
+        Some(format!("Add `raise` keyword"))
+    }
+}
+
+/// PLW0133
+pub(crate) fn useless_exception_statement(checker: &mut Checker, expr: &ast::StmtExpr) {
+    let Expr::Call(ast::ExprCall { func, .. }) = expr.value.as_ref() else {
+        return;
+    };
+
+    if is_builtin_exception(func, checker.semantic()) {
+        let mut diagnostic = Diagnostic::new(UselessExceptionStatement, expr.range());
+        diagnostic.set_fix(Fix::unsafe_edit(Edit::insertion(
+            "raise ".to_string(),
+            expr.start(),
+        )));
+        checker.diagnostics.push(diagnostic);
+    }
+}
+
+/// Returns `true` if the given expression is a builtin exception.
+///
+/// See: <https://docs.python.org/3/library/exceptions.html#exception-hierarchy>
+fn is_builtin_exception(expr: &Expr, semantic: &SemanticModel) -> bool {
+    return semantic.resolve_call_path(expr).is_some_and(|call_path| {
+        matches!(
+            call_path.as_slice(),
+            [
+                "",
+                "SystemExit"
+                    | "Exception"
+                    | "ArithmeticError"
+                    | "AssertionError"
+                    | "AttributeError"
+                    | "BufferError"
+                    | "EOFError"
+                    | "ImportError"
+                    | "LookupError"
+                    | "IndexError"
+                    | "KeyError"
+                    | "MemoryError"
+                    | "NameError"
+                    | "ReferenceError"
+                    | "RuntimeError"
+                    | "NotImplementedError"
+                    | "StopIteration"
+                    | "SyntaxError"
+                    | "SystemError"
+                    | "TypeError"
+                    | "ValueError"
+            ]
+        )
+    });
+}