[flake8-errmsg] Extend EM101 to support byte strings

crates/ruff_linter/resources/test/fixtures/flake8_errmsg/EM101_byte_string.py

@@ -0,0 +1,6 @@
+def f_byte():
+    raise RuntimeError(b"This is an example exception")
+
+
+def f_byte_empty():
+    raise RuntimeError(b"")

crates/ruff_linter/src/preview.rs

@@ -94,3 +94,8 @@ pub(crate) const fn is_ignore_init_files_in_useless_alias_enabled(
 pub(crate) const fn is_invalid_async_mock_access_check_enabled(settings: &LinterSettings) -> bool {
     settings.preview.is_enabled()
 }
+
+// https://github.com/astral-sh/ruff/pull/18867
+pub(crate) const fn is_raise_exception_byte_string_enabled(settings: &LinterSettings) -> bool {
+    settings.preview.is_enabled()
+}

crates/ruff_linter/src/rules/flake8_errmsg/mod.rs

@@ -9,6 +9,7 @@ mod tests {
     use anyhow::Result;
 
     use crate::registry::Rule;
+    use crate::settings::types::PreviewMode;
     use crate::test::test_path;
     use crate::{assert_diagnostics, settings};
 
@@ -44,4 +45,17 @@ mod tests {
         assert_diagnostics!("custom", diagnostics);
         Ok(())
     }
+
+    #[test]
+    fn preview_string_exception() -> Result<()> {
+        let diagnostics = test_path(
+            Path::new("flake8_errmsg/EM101_byte_string.py"),
+            &settings::LinterSettings {
+                preview: PreviewMode::Enabled,
+                ..settings::LinterSettings::for_rule(Rule::RawStringInException)
+            },
+        )?;
+        assert_diagnostics!("preview", diagnostics);
+        Ok(())
+    }
 }

crates/ruff_linter/src/rules/flake8_errmsg/rules/string_in_exception.rs

@@ -7,12 +7,16 @@ use ruff_text_size::Ranged;
 
 use crate::Locator;
 use crate::checkers::ast::Checker;
+use crate::preview::is_raise_exception_byte_string_enabled;
 use crate::registry::Rule;
 use crate::{Edit, Fix, FixAvailability, Violation};
 
 /// ## What it does
 /// Checks for the use of string literals in exception constructors.
 ///
+/// In [preview], this rule checks for byte string literals in
+/// exception constructors.
+///
 /// ## Why is this bad?
 /// Python includes the `raise` in the default traceback (and formatters
 /// like Rich and IPython do too).
@@ -47,6 +51,8 @@ use crate::{Edit, Fix, FixAvailability, Violation};
 ///     raise RuntimeError(msg)
 /// RuntimeError: 'Some value' is incorrect
 /// ```
+///
+/// [preview]: https://docs.astral.sh/ruff/preview/
 #[derive(ViolationMetadata)]
 pub(crate) struct RawStringInException;
 
@@ -203,6 +209,28 @@ pub(crate) fn string_in_exception(checker: &Checker, stmt: &Stmt, exc: &Expr) {
                         }
                     }
                 }
+                // Check for byte string literals.
+                Expr::BytesLiteral(ast::ExprBytesLiteral { value: bytes, .. }) => {
+                    if checker.settings().rules.enabled(Rule::RawStringInException) {
+                        if bytes.len() >= checker.settings().flake8_errmsg.max_string_length
+                            && is_raise_exception_byte_string_enabled(checker.settings())
+                        {
+                            let mut diagnostic =
+                                checker.report_diagnostic(RawStringInException, first.range());
+                            if let Some(indentation) =
+                                whitespace::indentation(checker.source(), stmt)
+                            {
+                                diagnostic.set_fix(generate_fix(
+                                    stmt,
+                                    first,
+                                    indentation,
+                                    checker.stylist(),
+                                    checker.locator(),
+                                ));
+                            }
+                        }
+                    }
+                }
                 // Check for f-strings.
                 Expr::FString(_) => {
                     if checker.is_rule_enabled(Rule::FStringInException) {

crates/ruff_linter/src/rules/flake8_errmsg/snapshots/ruff_linter__rules__flake8_errmsg__tests__preview.snap

@@ -0,0 +1,35 @@
+---
+source: crates/ruff_linter/src/rules/flake8_errmsg/mod.rs
+---
+EM101_byte_string.py:2:24: EM101 [*] Exception must not use a string literal, assign to variable first
+  |
+1 | def f_byte():
+2 |     raise RuntimeError(b"This is an example exception")
+  |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ EM101
+  |
+  = help: Assign to variable; remove string literal
+
+ℹ Unsafe fix
+1 1 | def f_byte():
+2   |-    raise RuntimeError(b"This is an example exception")
+  2 |+    msg = b"This is an example exception"
+  3 |+    raise RuntimeError(msg)
+3 4 | 
+4 5 | 
+5 6 | def f_byte_empty():
+
+EM101_byte_string.py:6:24: EM101 [*] Exception must not use a string literal, assign to variable first
+  |
+5 | def f_byte_empty():
+6 |     raise RuntimeError(b"")
+  |                        ^^^ EM101
+  |
+  = help: Assign to variable; remove string literal
+
+ℹ Unsafe fix
+3 3 | 
+4 4 | 
+5 5 | def f_byte_empty():
+6   |-    raise RuntimeError(b"")
+  6 |+    msg = b""
+  7 |+    raise RuntimeError(msg)