Make ARG002 compatible with EM101 when raising NotImplementedError

crates/ruff_linter/resources/test/fixtures/flake8_unused_arguments/ARG.py

@@ -55,6 +55,18 @@ def f(cls, x):
     def f(x):
         print("Hello, world!")
 
+    def f(self, x):
+        msg[0] = "..."
+        raise NotImplementedError(msg)
+
+    def f(self, x):
+        msg = "..."
+        raise NotImplementedError(foo)
+
+    def f(self, x):
+        msg = "..."
+        raise NotImplementedError("must use msg")
+
     ###
     # Unused arguments attached to empty functions (OK).
     ###
@@ -107,6 +119,15 @@ def f(self, x):
     def f(self, x):
         raise NotImplemented("...")
 
+    def f(self, x):
+        msg = "..."
+        raise NotImplementedError(msg)
+
+    def f(self, x, y):
+        """Docstring."""
+        msg = f"{x}..."
+        raise NotImplementedError(msg)
+
     ###
     # Unused functions attached to abstract methods (OK).
     ###

crates/ruff_linter/src/rules/flake8_unused_arguments/rules/unused_arguments.rs

@@ -1,6 +1,6 @@
 use regex::Regex;
 use ruff_python_ast as ast;
-use ruff_python_ast::{Parameter, Parameters};
+use ruff_python_ast::{Parameter, Parameters, Stmt, StmtExpr, StmtFunctionDef, StmtRaise};
 
 use ruff_diagnostics::DiagnosticKind;
 use ruff_diagnostics::{Diagnostic, Violation};
@@ -311,6 +311,60 @@ fn call<'a>(
     }));
 }
 
+/// Returns `true` if a function appears to be a base class stub. In other
+/// words, if it matches the following syntax:
+///
+/// ```text
+/// variable = <string | f-string>
+/// raise NotImplementedError(variable)
+/// ```
+///
+/// See also [`is_stub`]. We're a bit more generous in what is considered a
+/// stub in this rule to avoid clashing with [`EM101`].
+///
+/// [`is_stub`]: function_type::is_stub
+/// [`EM101`]: https://docs.astral.sh/ruff/rules/raw-string-in-exception/
+fn is_not_implemented_stub_with_variable(function_def: &StmtFunctionDef) -> bool {
+    // Ignore doc-strings.
+    let statements = match function_def.body.as_slice() {
+        [Stmt::Expr(StmtExpr { value, .. }), rest @ ..] if value.is_string_literal_expr() => rest,
+        _ => &function_def.body,
+    };
+
+    let [Stmt::Assign(ast::StmtAssign { targets, value, .. }), Stmt::Raise(StmtRaise {
+        exc: Some(exception),
+        ..
+    })] = statements
+    else {
+        return false;
+    };
+
+    if !matches!(**value, ast::Expr::StringLiteral(_) | ast::Expr::FString(_)) {
+        return false;
+    }
+
+    let ast::Expr::Call(ast::ExprCall {
+        func, arguments, ..
+    }) = &**exception
+    else {
+        return false;
+    };
+
+    if !matches!(&**func, ast::Expr::Name(name) if name.id == "NotImplementedError") {
+        return false;
+    }
+
+    let [argument] = &*arguments.args else {
+        return false;
+    };
+
+    let [target] = targets.as_slice() else {
+        return false;
+    };
+
+    argument.as_name_expr().map(ast::ExprName::id) == target.as_name_expr().map(ast::ExprName::id)
+}
+
 /// ARG001, ARG002, ARG003, ARG004, ARG005
 pub(crate) fn unused_arguments(
     checker: &Checker,
@@ -345,6 +399,7 @@ pub(crate) fn unused_arguments(
                 function_type::FunctionType::Function => {
                     if checker.enabled(Argumentable::Function.rule_code())
                         && !function_type::is_stub(function_def, checker.semantic())
+                        && !is_not_implemented_stub_with_variable(function_def)
                         && !visibility::is_overload(decorator_list, checker.semantic())
                     {
                         function(
@@ -364,6 +419,7 @@ pub(crate) fn unused_arguments(
                 function_type::FunctionType::Method => {
                     if checker.enabled(Argumentable::Method.rule_code())
                         && !function_type::is_stub(function_def, checker.semantic())
+                        && !is_not_implemented_stub_with_variable(function_def)
                         && (!visibility::is_magic(name)
                             || visibility::is_init(name)
                             || visibility::is_new(name)
@@ -389,6 +445,7 @@ pub(crate) fn unused_arguments(
                 function_type::FunctionType::ClassMethod => {
                     if checker.enabled(Argumentable::ClassMethod.rule_code())
                         && !function_type::is_stub(function_def, checker.semantic())
+                        && !is_not_implemented_stub_with_variable(function_def)
                         && (!visibility::is_magic(name)
                             || visibility::is_init(name)
                             || visibility::is_new(name)
@@ -414,6 +471,7 @@ pub(crate) fn unused_arguments(
                 function_type::FunctionType::StaticMethod => {
                     if checker.enabled(Argumentable::StaticMethod.rule_code())
                         && !function_type::is_stub(function_def, checker.semantic())
+                        && !is_not_implemented_stub_with_variable(function_def)
                         && (!visibility::is_magic(name)
                             || visibility::is_init(name)
                             || visibility::is_new(name)

crates/ruff_linter/src/rules/flake8_unused_arguments/snapshots/ruff_linter__rules__flake8_unused_arguments__tests__ARG002_ARG.py.snap

@@ -28,13 +28,41 @@ ARG.py:43:16: ARG002 Unused method argument: `x`
 44 |         print("Hello, world!")
    |
 
-ARG.py:192:24: ARG002 Unused method argument: `x`
+ARG.py:58:17: ARG002 Unused method argument: `x`
+   |
+56 |         print("Hello, world!")
+57 | 
+58 |     def f(self, x):
+   |                 ^ ARG002
+59 |         msg[0] = "..."
+60 |         raise NotImplementedError(msg)
+   |
+
+ARG.py:62:17: ARG002 Unused method argument: `x`
+   |
+60 |         raise NotImplementedError(msg)
+61 | 
+62 |     def f(self, x):
+   |                 ^ ARG002
+63 |         msg = "..."
+64 |         raise NotImplementedError(foo)
+   |
+
+ARG.py:66:17: ARG002 Unused method argument: `x`
+   |
+64 |         raise NotImplementedError(foo)
+65 | 
+66 |     def f(self, x):
+   |                 ^ ARG002
+67 |         msg = "..."
+68 |         raise NotImplementedError("must use msg")
+   |
+
+ARG.py:213:24: ARG002 Unused method argument: `x`
     |
-190 | ###
-191 | class C:
-192 |     def __init__(self, x) -> None:
+211 | ###
+212 | class C:
+213 |     def __init__(self, x) -> None:
     |                        ^ ARG002
-193 |         print("Hello, world!")
+214 |         print("Hello, world!")
     |
-
-