Auto merge of rust-lang#16066 - Young-Flash:auto_remove_brace, r=lnicola

fix: auto remove unnecessary braces after remove unused imports

before
![before](https://github.com/rust-lang/rust-analyzer/assets/71162630/8d44f955-f84f-4a92-b13f-5a2dee2ded36)

after
![after](https://github.com/rust-lang/rust-analyzer/assets/71162630/1eab23c8-39bd-4711-97c1-d483ce400a18)

Author: bors

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

@@ -423,7 +423,7 @@ mod z {
 struct X();
 struct Y();
 mod z {
-    use super::{X};
+    use super::X;
 
     fn w() {
         let x = X();
@@ -495,7 +495,7 @@ struct X();
 mod y {
     struct Y();
     mod z {
-        use crate::{X};
+        use crate::X;
         fn f() {
             let x = X();
         }
@@ -526,7 +526,7 @@ struct X();
 mod y {
     struct Y();
     mod z {
-        use crate::{y::Y};
+        use crate::y::Y;
         fn f() {
             let y = Y();
         }
@@ -536,6 +536,79 @@ mod y {
         );
     }
 
+    #[test]
+    fn remove_unused_auto_remove_brace_nested() {
+        check_assist(
+            remove_unused_imports,
+            r#"
+mod a {
+    pub struct A();
+}
+mod b {
+    struct F();
+    mod c {
+        $0use {{super::{{
+            {d::{{{{{{{S, U}}}}}}}},
+            {{{{e::{H, L, {{{R}}}}}}}},
+            F, super::a::A
+        }}}};$0
+        fn f() {
+            let f = F();
+            let l = L();
+            let a = A();
+            let s = S();
+            let h = H();
+        }
+    }
+
+    mod d {
+        pub struct S();
+        pub struct U();
+    }
+
+    mod e {
+        pub struct H();
+        pub struct L();
+        pub struct R();
+    }
+}
+"#,
+            r#"
+mod a {
+    pub struct A();
+}
+mod b {
+    struct F();
+    mod c {
+        use super::{
+            d::S,
+            e::{H, L},
+            F, super::a::A
+        };
+        fn f() {
+            let f = F();
+            let l = L();
+            let a = A();
+            let s = S();
+            let h = H();
+        }
+    }
+
+    mod d {
+        pub struct S();
+        pub struct U();
+    }
+
+    mod e {
+        pub struct H();
+        pub struct L();
+        pub struct R();
+    }
+}
+"#,
+        );
+    }
+
     #[test]
     fn remove_nested_all_unused() {
         check_assist(

crates/syntax/src/ast/edit_in_place.rs

@@ -414,6 +414,7 @@ impl ast::UseTree {
                     u.remove_recursive();
                 }
             }
+            u.remove_unnecessary_braces();
         }
     }
 

crates/syntax/src/ast/node_ext.rs

@@ -11,7 +11,7 @@ use rowan::{GreenNodeData, GreenTokenData};
 
 use crate::{
     ast::{self, support, AstNode, AstToken, HasAttrs, HasGenericParams, HasName, SyntaxNode},
-    NodeOrToken, SmolStr, SyntaxElement, SyntaxToken, TokenText, T,
+    ted, NodeOrToken, SmolStr, SyntaxElement, SyntaxToken, TokenText, T,
 };
 
 impl ast::Lifetime {
@@ -323,6 +323,10 @@ impl ast::UseTree {
     pub fn is_simple_path(&self) -> bool {
         self.use_tree_list().is_none() && self.star_token().is_none()
     }
+
+    pub fn parent_use_tree_list(&self) -> Option<ast::UseTreeList> {
+        self.syntax().parent().and_then(ast::UseTreeList::cast)
+    }
 }
 
 impl ast::UseTreeList {
@@ -340,6 +344,27 @@ impl ast::UseTreeList {
             .find_map(ast::Comment::cast)
             .is_some()
     }
+
+    /// Remove the unnecessary braces in current `UseTreeList`
+    pub fn remove_unnecessary_braces(mut self) {
+        let remove_brace_in_use_tree_list = |u: &ast::UseTreeList| {
+            let use_tree_count = u.use_trees().count();
+            if use_tree_count == 1 {
+                u.l_curly_token().map(ted::remove);
+                u.r_curly_token().map(ted::remove);
+            }
+        };
+
+        // take `use crate::{{{{A}}}}` for example
+        // the below remove the innermost {}, got `use crate::{{{A}}}`
+        remove_brace_in_use_tree_list(&self);
+
+        // the below remove othe unnecessary {}, got `use crate::A`
+        while let Some(parent_use_tree_list) = self.parent_use_tree().parent_use_tree_list() {
+            remove_brace_in_use_tree_list(&parent_use_tree_list);
+            self = parent_use_tree_list;
+        }
+    }
 }
 
 impl ast::Impl {