Add remove_mut assist

crates/ra_assists/src/doc_tests/generated.rs

@@ -548,6 +548,23 @@ fn main() {
     )
 }
 
+#[test]
+fn doctest_remove_mut() {
+    check(
+        "remove_mut",
+        r#####"
+impl Walrus {
+    fn feed(&mut<|> self, amount: u32) {}
+}
+"#####,
+        r#####"
+impl Walrus {
+    fn feed(&self, amount: u32) {}
+}
+"#####,
+    )
+}
+
 #[test]
 fn doctest_replace_if_let_with_match() {
     check(

crates/ra_assists/src/handlers/remove_mut.rs

@@ -0,0 +1,32 @@
+use ra_syntax::{SyntaxKind, TextRange, T};
+
+use crate::{Assist, AssistCtx, AssistId};
+
+// Assist: remove_mut
+//
+// Removes the `mut` keyword.
+//
+// ```
+// impl Walrus {
+//     fn feed(&mut<|> self, amount: u32) {}
+// }
+// ```
+// ->
+// ```
+// impl Walrus {
+//     fn feed(&self, amount: u32) {}
+// }
+// ```
+pub(crate) fn remove_mut(ctx: AssistCtx) -> Option<Assist> {
+    let mut_token = ctx.find_token_at_offset(T![mut])?;
+    let delete_from = mut_token.text_range().start();
+    let delete_to = match mut_token.next_token() {
+        Some(it) if it.kind() == SyntaxKind::WHITESPACE => it.text_range().end(),
+        _ => mut_token.text_range().end(),
+    };
+
+    ctx.add_assist(AssistId("remove_mut"), "Remove `mut` keyword", |edit| {
+        edit.set_cursor(delete_from);
+        edit.delete(TextRange::from_to(delete_from, delete_to));
+    })
+}

crates/ra_assists/src/lib.rs

@@ -108,6 +108,7 @@ mod handlers {
     mod introduce_variable;
     mod inline_local_variable;
     mod raw_string;
+    mod remove_mut;
     mod replace_if_let_with_match;
     mod split_import;
     mod remove_dbg;
@@ -147,6 +148,7 @@ mod handlers {
             raw_string::make_raw_string,
             raw_string::make_usual_string,
             raw_string::remove_hash,
+            remove_mut::remove_mut,
             early_return::convert_to_guarded_return,
             auto_import::auto_import,
         ]

docs/user/assists.md

@@ -527,6 +527,22 @@ fn main() {
 }
 ```
 
+## `remove_mut`
+
+Removes the `mut` keyword.
+
+```rust
+// BEFORE
+impl Walrus {
+    fn feed(&mut┃ self, amount: u32) {}
+}
+
+// AFTER
+impl Walrus {
+    fn feed(&self, amount: u32) {}
+}
+```
+
 ## `replace_if_let_with_match`
 
 Replaces `if let` with an else branch with a `match` expression.