Add ide-assist: toggle_lint_attr

Change lint attribute level.

Example
---
```
#[$0allow(dead_code)]
fn foo() {}
```
->
```
#[expect(dead_code)]
fn foo() {}
```

---

```
#[$0forbid(dead_code)]
fn foo() {}
```
->
```
#[deny(dead_code)]
fn foo() {}
```

crates/ide-assists/src/handlers/toggle_lint_attr.rs

@@ -0,0 +1,116 @@
+use ide_db::assists::AssistId;
+use syntax::{AstNode, ast};
+
+use crate::{AssistContext, Assists};
+
+// Assist: toggle_lint_attr
+//
+// Change lint attribute level.
+//
+// ```
+// #[$0allow(dead_code)]
+// fn foo() {}
+// ```
+// ->
+// ```
+// #[expect(dead_code)]
+// fn foo() {}
+// ```
+//
+// ---
+//
+// ```
+// #[$0forbid(dead_code)]
+// fn foo() {}
+// ```
+// ->
+// ```
+// #[deny(dead_code)]
+// fn foo() {}
+// ```
+pub(crate) fn toggle_lint_attr(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
+    let path = ctx.find_node_at_offset::<ast::Path>()?;
+    let name = path.as_single_name_ref()?;
+    let _meta = ast::Meta::cast(path.syntax().parent()?)?;
+
+    let target = name.syntax().text_range();
+    for &toggled_name in toggled_lint(&name)? {
+        acc.add(
+            AssistId::refactor("toggle_lint_attr"),
+            format!("Replace `{name}` to `{toggled_name}`"),
+            target,
+            |builder| {
+                builder.replace(target, toggled_name);
+            },
+        )?;
+    }
+    Some(())
+}
+
+fn toggled_lint(name: &ast::NameRef) -> Option<&[&'static str]> {
+    Some(match name.text().as_str() {
+        "allow" => &["expect", "warn"],
+        "expect" => &["allow"],
+        "warn" => &["deny", "allow"],
+        "deny" => &["forbid", "warn"],
+        "forbid" => &["deny"],
+        _ => return None,
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn test_toggle_lint_attr() {
+        check_assist(
+            toggle_lint_attr,
+            "
+#[$0allow(unused_mut)]
+fn foo() {}
+            ",
+            "
+#[expect(unused_mut)]
+fn foo() {}
+            ",
+        );
+
+        check_assist(
+            toggle_lint_attr,
+            "
+#[$0expect(unused_mut)]
+fn foo() {}
+            ",
+            "
+#[allow(unused_mut)]
+fn foo() {}
+            ",
+        );
+
+        check_assist(
+            toggle_lint_attr,
+            "
+#[$0forbid(unused_mut)]
+fn foo() {}
+            ",
+            "
+#[deny(unused_mut)]
+fn foo() {}
+            ",
+        );
+    }
+
+    #[test]
+    fn test_toggle_lint_attr_not_applicable_other_attr() {
+        check_assist_not_applicable(
+            toggle_lint_attr,
+            "
+#[$0inline(never)]
+fn foo() {}
+            ",
+        );
+    }
+}

crates/ide-assists/src/lib.rs

@@ -222,6 +222,7 @@ mod handlers {
     mod term_search;
     mod toggle_async_sugar;
     mod toggle_ignore;
+    mod toggle_lint_attr;
     mod toggle_macro_delimiter;
     mod unmerge_imports;
     mod unmerge_match_arm;
@@ -365,6 +366,7 @@ mod handlers {
             toggle_async_sugar::desugar_async_into_impl_future,
             toggle_async_sugar::sugar_impl_future_into_async,
             toggle_ignore::toggle_ignore,
+            toggle_lint_attr::toggle_lint_attr,
             toggle_macro_delimiter::toggle_macro_delimiter,
             unmerge_match_arm::unmerge_match_arm,
             unmerge_imports::unmerge_imports,

crates/ide-assists/src/tests/generated.rs

@@ -3389,6 +3389,36 @@ fn arithmetics {
     )
 }
 
+#[test]
+fn doctest_toggle_lint_attr() {
+    check_doc_test(
+        "toggle_lint_attr",
+        r#####"
+#[$0allow(dead_code)]
+fn foo() {}
+"#####,
+        r#####"
+#[expect(dead_code)]
+fn foo() {}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_toggle_lint_attr_1() {
+    check_doc_test(
+        "toggle_lint_attr",
+        r#####"
+#[$0forbid(dead_code)]
+fn foo() {}
+"#####,
+        r#####"
+#[deny(dead_code)]
+fn foo() {}
+"#####,
+    )
+}
+
 #[test]
 fn doctest_toggle_macro_delimiter() {
     check_doc_test(