Remove the deprecated E999 rule code

crates/ruff/tests/integration_test.rs

@@ -840,7 +840,7 @@ fn stdin_multiple_parse_error() {
 
 #[test]
 fn parse_error_not_included() {
-    // Select any rule except for `E999`, syntax error should still be shown.
+    // Parse errors are always shown
     let mut cmd = RuffCheck::default().args(["--select=I"]).build();
     assert_cmd_snapshot!(cmd
         .pass_stdin("foo =\n"), @r"
@@ -859,27 +859,6 @@ fn parse_error_not_included() {
     ");
 }
 
-#[test]
-fn deprecated_parse_error_selection() {
-    let mut cmd = RuffCheck::default().args(["--select=E999"]).build();
-    assert_cmd_snapshot!(cmd
-        .pass_stdin("foo =\n"), @r"
-    success: false
-    exit_code: 1
-    ----- stdout -----
-    -:1:6: SyntaxError: Expected an expression
-      |
-    1 | foo =
-      |      ^
-      |
-
-    Found 1 error.
-
-    ----- stderr -----
-    warning: Rule `E999` is deprecated and will be removed in a future release. Syntax errors will always be shown regardless of whether this rule is selected or not.
-    ");
-}
-
 #[test]
 fn full_output_preview() {
     let mut cmd = RuffCheck::default().args(["--preview"]).build();

crates/ruff/tests/snapshots/show_settings__display_default_settings.snap

@@ -88,7 +88,6 @@ linter.rules.enabled = [
 	ambiguous-class-name (E742),
 	ambiguous-function-name (E743),
 	io-error (E902),
-	syntax-error (E999),
 	unused-import (F401),
 	import-shadowed-by-loop-var (F402),
 	undefined-local-with-import-star (F403),
@@ -150,7 +149,6 @@ linter.rules.should_fix = [
 	ambiguous-class-name (E742),
 	ambiguous-function-name (E743),
 	io-error (E902),
-	syntax-error (E999),
 	unused-import (F401),
 	import-shadowed-by-loop-var (F402),
 	undefined-local-with-import-star (F403),

crates/ruff_linter/src/codes.rs

@@ -126,7 +126,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Pycodestyle, "E742") => (RuleGroup::Stable, rules::pycodestyle::rules::AmbiguousClassName),
         (Pycodestyle, "E743") => (RuleGroup::Stable, rules::pycodestyle::rules::AmbiguousFunctionName),
         (Pycodestyle, "E902") => (RuleGroup::Stable, rules::pycodestyle::rules::IOError),
-        (Pycodestyle, "E999") => (RuleGroup::Deprecated, rules::pycodestyle::rules::SyntaxError),
+        (Pycodestyle, "E999") => (RuleGroup::Removed, rules::pycodestyle::rules::SyntaxError),
 
         // pycodestyle warnings
         (Pycodestyle, "W191") => (RuleGroup::Stable, rules::pycodestyle::rules::TabIndentation),

crates/ruff_linter/src/rules/pycodestyle/rules/errors.rs

@@ -68,9 +68,11 @@ pub struct SyntaxError {
 }
 
 impl Violation for SyntaxError {
-    #[derive_message_formats]
     fn message(&self) -> String {
-        let SyntaxError { message } = self;
-        format!("SyntaxError: {message}")
+        unreachable!("E999 has been removed")
+    }
+
+    fn message_formats() -> &'static [&'static str] {
+        &["SyntaxError"]
     }
 }

crates/ruff_workspace/src/configuration.rs

@@ -1000,13 +1000,9 @@ impl LintConfiguration {
         if preview.mode.is_disabled() {
             for selection in deprecated_selectors.iter().sorted() {
                 let (prefix, code) = selection.prefix_and_code();
-                let rule = format!("{prefix}{code}");
-                let mut message =
-                    format!("Rule `{rule}` is deprecated and will be removed in a future release.");
-                if matches!(rule.as_str(), "E999") {
-                    message.push_str(" Syntax errors will always be shown regardless of whether this rule is selected or not.");
-                }
-                warn_user_once_by_message!("{message}");
+                warn_user_once_by_message!(
+                    "Rule `{prefix}{code}` is deprecated and will be removed in a future release."
+                );
             }
         } else {
             let deprecated_selectors = deprecated_selectors.iter().sorted().collect::<Vec<_>>();
@@ -1632,7 +1628,6 @@ mod tests {
             Rule::AmbiguousClassName,
             Rule::AmbiguousFunctionName,
             Rule::IOError,
-            Rule::SyntaxError,
             Rule::TabIndentation,
             Rule::TrailingWhitespace,
             Rule::MissingNewlineAtEndOfFile,